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SCIENCE FOR PRIMARY TEACHERS
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University
THE WEATHER
AllAlNMENT TARGETS ADDRESSED IN
'THE WEATHER': AT9 AND AT16
4 ATMOSPHERIC PRESSURE
STUDY GUIDE
Study notes
Activity 1 : Weather maps and
forecasts
Teaching notes
lnvestigation 3: Demonstrating air
pressure
Key points
1 INTRODUCTION
AT9: level 1
Study notes
Teaching notes
Key point
2 THE ATMOSPHERE AND
THE ENERGY BUDGET
AT9: levels 3 and 4; AT16: level 1
Study notes
Teaching notes
lnvestigation 1 : Testing hats
lnvestigation 2: Making a
thermometer
Key points
3 WATER IN THE ATMOSPHERE
AT9: levels 1,2,4 and 5
Study notes
Teaching notes
Key points
AT9: level 3
5 WIND
AT9: levels 1 to 5
Study notes
Teaching notes
Key points
6 IDEAS FOR RECORDING AND
USING DATA OBTAINED FROM A
WEATHER STATION
7 CONCLUSIONS
RESOURCES
ACKNOWLEDGEMENTS
CENTRE FOR SCIENCE EDUCATION
32
THE WEATHER
ATTAINMENT TARGETS
ADDRESSED IN 'THE WEATHER':
AT9 AND AT16
AllAlNMENT TARGET 9: EARTH AND
ATMOSPHERE
Pupils should develop their knowledge and understanding of the structure and
main features of the Earth, the atmosphere and their changes over time.
Key
stage
1
Programme of study
Children should collect, and find differences
and similarities in, natural materials found
in their locality, including rocks and soil.
They should compare samples with those
represented or described at second hand.
They should observe and record the changes
in the weather and relate these to their
everyday activities.
Level
Statement of attainment
Pupils should
know that there is a variety of weather
conditions
be'able to describe changes in the weather
know that there are patterns in the weather
which are related to seasonal changes
know that the weather has a powerful effect
on people's lives
be able to record the weather over a period of
time, in words, drawings and charts or other
forms of communication
be able to sort natural materials into broad
groups according to observable features
2
Children should investigate natural
materials (rocks, minerals, soils), should
sort them according to simple criteria, and
relate them to their uses and origins, using
books and other sources. They should be
aware of local distributions of some types
of natural materials (sands, soils, rocks).
They should observe, through urban or
rural fieldwork, how weather affects natural
materials (including plants) in their
surroundings and how soil develops. They
should also consider the major geological
events which change the surface of the
Earth. They should have the opportunity to
make regular, quantitative observations and
keep records of the weather and the seasons
of the year.
be able to describe from their observations
some of the effects of weathering on
buildings and on the landscape
know that air is all around us
understand how weathering of rocks leads to
the formation of different types of soil
be able to give an account of an investigation
of some natural material (rock or soil)'
be able to understand and interpret common
meteorological symbols as used in the media
be able to measure temperature, rainfall, wind
speed and direction; be able to explain that
wind is air in motion
know that climate determines the success of
agriculture and understand the impact of
,
occasional catastrophic events
know that landscapes are formed by a number
of agents, including Earth movements,
weathering, erosion and deposition, and that
these act over different time-scales
be able to explain how earthquakes and
volcanoes are associated with the formation of
landforms
be able to explain the water cycle
SCIENCE FOR PRIMARY TEACHERS
AlTAlNMENT TARGET 16: THE EARTH IN SPACE
Pupils should develop their knowledge and understanding of the relative positions
and movement of the Earth, Moon, Sun and Solar System within the Universe.
Key
stage
1
Programme of study
Children should observe closely their local
natural environment to detect seasonal
changes, including day length, weather and
changes in plants and animals, and relate
these changes to the passage of time. They
should observe, over a period of time, the
length of the day, the position of the Sun,
and where possible the Moon, in the sky.
They should investigate the use of a sundial
as a means of observing the passage of
time.
Level
1
2
Statement of attainment
Pupils should
a be able to describe through talking, or other
appropriate means, the seasonal changes that
occur in the weather and in living things
b know the danger of looking directly at the
Sun
c be able to describe, in relation to their home
or school, the apparent daily motion of the
Sun across the sky
a be able to explain why night occurs
b know that day length changes throughout the
YW
c know that we live on a large, spherical, selfcontained planet, called Earth
d know that the Earth, Moon and Sun are
separate bodies
Children should be given the opportunity to
investigate changes in the night sky, in
particular the position of the Moon,
through direct observation and by using
secondary sources. Children should use a
simple model of the Solar System to
attempt explanations of day and night, year
length and changes in the aspect of the
Moon and elevation of the Sun. They
should be introduced to the principle of the
sundial as a means of noting the passage of
time. They should learn about the position
and motion of the Earth, Moon and Sun
relative to each other.
3
a know that the inclination of the Sun in the
sky changes during the year
b be able to measure time with a sundial
4
a know that the phases of the Moon change in
a regular and predictable manner
b know that the Solar System is made up of the
Sun and planets, and have an idea of its scale
c understand that the Sun is a star
3
a be able to relate a simple model of the Solar
System to daylnight and year length, changes
of day length, seasonal changes and changes
in the inclination of the Sun
b be able to observe and record the shape and
surface shading of the phases of the Moon
over a period of time
THE WEATHER
TABLE 1 Levels of the attainment targets covered in 'The weather'
ATs
Level 1
a
1
2
3
4
5
6
9
a
10 1 1 12
1 3 14 15 1 6
a
b
C
L
Level
Level
Level 4
Level 5
Note: a, b, c, etc. refer to the statements of attainment. For the complete
statements, please see pp. 3 and 4.
SCIENCE FOR PRIMARY TEACHERS
STUDY GUIDE
'The weather' considers the different aspects that make up our weather and
suggests approaches to teaching and learning about this topic in the primary
classroom. The scientific information provided will enable non-specialist teachers
to understand some of the main concepts of meteorology and plan their teaching
of the topic more effectively.
This material has not been designed to accompany an S102 Unit: its structure is
similar to that of the Study Commentaries but the Study notes are complete in
themselves and do not require you to refer to any other Units. The elements of
weather are covered in Sections 2 to 5 together with information about how each
element can be measured.
1 INTRODUCTION
1
Main attainment target and levels addressed in Section l: AT9: level 1
1
STUDY NOTES
Before we embark on a study of various elements of the weather, it is important
to differentiate between weather and climate. Climate can be defined as long-term
average weather conditions at a particular place, whereas weather is the day-to-day
state of the atmosphere. Weather occurs everywhere. The main elements involved
are the Sun, and the wind and water vapour in the atmosphere. These all work
together to create the endless cycle of events we call the weather.
TEACHING NOTES
In the classroom, work on aspects of the weather relates mainly to AT1, AT9
and AT16, and presents many data-handling opportunities.
The study of weather offers children a variety of experiences, and the topic can
arise from, or be linked to, a curriculum area other than science, such as
technology, mathematics or language. In geography and history, for example, a
link can be made between different lifestyles and settlements and the prevailing
weather. You may have children in your class who have lived in different
climates: they could be encouraged to share their experiences. Since the weather
is such a vast topic, you may feel that it is preferable to concentrate on a single
aspect of it at a time. In this case one class may study one aspect, or groups
within a class may work on different aspects. These could include rainfall and the
water cycle, wind power and the changing seasons. Do remember, though, that if
children study different aspects separately, they will need opportunities to make
links and see the interrelationships between the various elements.
An important part of weather studies is the taking of measurements. Suggestions
are included in each Section for ways in which simple weather measurements can
be taken using instruments that can be made with the minimum of cost and
effort.
Many schools and classes will already have suitable instruments; others can be
made by the children for taking crude but effective weather readings to build up a
weather record. Readings taken with such instruments will enable you to see the
general behaviour of the atmosphere, and the skills involved in taking
measurements, reading scales and recording the results will be no less valuable
for the children than if they had used more sophisticated and expensive
instruments. If you wish to set up a weather station whose records can be used
for a detailed study of the area, however, or perhaps that are acceptable to the
Meteorological Office as an official record of your local weather, you should refer
to the various publications of the Meteorological Office.
THE WEATHER
KEY POINT
The constant changes in the atmosphere at any one time, or over a short
period of time (a day or a week), are what we call the weather. The main
elements involved are the Sun, the wind and water vapour in the atmosphere.
2 THE ATMOSPHERE AND THE
ENERGY BUDGET
Main attainment target and levels addressed in Section 2: AT9: levels 3
and 4; AT16: level 1
STUDY NOTES
THE AIR AROUND US
The Earth is surrounded by a mixture of gases known as the atmosphere. We are,
in effect, living at the bottom of a sea of air. The atmosphere is most dense at
sea-level and thins out as it stretches upwards. At about 50 km there is almost a
vacuum. The atmosphere provides us with the air we breathe, insulates the Earth
from excessive heating and cooling and filters out harmful radiation from the
Sun.
Nine-tenths of all the substance of the atmosphere is in the layer from Om
altitude (sea-level) to about 15km. When dry, this lower layer consists mainly
of nitrogen (78%), oxygen (21%) and argon (1%) (see S102 Units 28-29,
Section 9). The rest is made up of trace gases, including carbon dioxide, neon,
helium, ozone, hydrogen and krypton. Air also contains varying amounts of
water vapour, from less than 1% up to 4% (by volume). There is usually a
higher proportion of water vapour in the air near the Earth's surface. In addition
to being present as a water vapour which is an odourless, colourless gas, water
also occurs as a liquid, forming fog, cloud droplets and rain, and as a solid,
forming snow and hail.
The gases of the air are mixed together, not chemically combined (see
'Introducing chemistry concepts' to remind yourself about mixtures), so the
composition of the air varies slightly over different parts of the world. The
greatest variation is in the amount of water vapour and pollutants present in the
air. Pollutants include excess carbon dioxide, sulphur dioxide and various
nitrogen oxides. Even a small town of only 10000 inhabitants can produce more
than 5 tonnes of polluting soot and toxic waste gases every day from burning
coal, oil and other fuels. The Section on 'Fuels' in the chemistry materials
shows some of the effects of these pollutants. In addition, dust particles, plant
spores and pollen grains float through the air, while near the coast salt from seaspray and sand particles are present in the air. Volcanic eruptions, although fairly
rare, can pour many tonnes of fine ash and a variety of gases into the atmosphere
(see S102 Units 28-29, Section 9).
LAYERS OF THE ATMOSPHERE
The exploration of the upper atmosphere has become possible only in recent
times. Early climbers soon discovered that the thin mountain air made them
dizzy and sluggish, and in the 19th century the first balloonists to reach l 0 km
altitude narrowly escaped death from lack of oxygen. Today, high-altitude
balloonists and mountaineers climbing the tallest peaks, such as those in the
Himalayas, take supplies of oxygen with them. In the last thirty years or so,
pressurized aircraft, unmanned balloons with recording instruments, and satellites
launched by rockets have enabled us to find out more about the vertical structure
of the air.
SCIENCE FOR PRIMARY TEACHERS
The atmosphere consists of three main layers. The troposphere, which contains
90% .of the mass of the air, is the lowest, starting at the Earth's surface and
extending up to 8-15 km. Its upper boundary is known as the tropopause, which
is at its lowest height in polar regions and its highest near the Equator. The
temperature of the troposphere falls rapidly with increasing height, and at its
upper limit is about -60 "C. Our storms have their origins in the troposphere,
and it is within this layer that the weather happens.
The second layer, the stratosphere, reaches a height of about 50km above ground
level. Its lower boundary is the tropopause and it extends up to the stratopause.
Within the stratosphere the pressure decreases and the temperature rises from
about -60 "C to around 0°C. There is very little moisture and there are no
storms. Jet aircraft fly in the stratosphere because they can fly faster, using less
fuel, through the less dense air; in doing so, they also escape any bad weather
below.
The most striking feature of the stratosphere is a belt of ozone, which is
especially abundant around 15-30 km. (Ozone is a gas formed of molecules
containing three atoms of oxygen each.) This 'ozone layer' protects us by
absorbing some of the Sun's harmful ultraviolet rays. Without the ozone layer,
life on Earth as we know it today would be impossible. Ozone is constantly
being produced by the photochemical reactions caused by sunlight but soon
reverts to oxygen. This natural process is disrupted by manufactured gases such
as chlorofluorocarbons (CFCs), which have the effect of reducing the ozone
content. If a reduction in ozone occurs, more ultraviolet light can reach the
Earth's surface; the effects of this are at present a matter for controversy. It is
almost certain, however, that there is likely to be an increase in skin cancer.
Above the stratosphere is a belt in which the gases are even thinner and the
atoms are ionized (electrically charged) by the Sun's radiation. This is the
ionosphere; radio waves are reflected back and forwards between the upper and
lower boundaries of the ionosphere, and some return back to Earth; these would
otherwise travel out to space and be totally lost. It is also in the ionosphere, in
belts surrounding the North and South magnetic poles, that the beautiful colour
effects of the northern lights (the aurora borealis) and the southern lights (the
aurora australis) occur.
THE ENERGY BUDGET
Energy radiated from the Sun is absorbed by the Earth as heat. Most of the
radiation reaching the Earth from the Sun is visible light, which passes though
atmospheric carbon dioxide and water vapour and heats the Earth's surface. (The
very-short-wave ultraviolet radiation is largely absorbed by oxygen or ozone
higher in the atmosphere.) Only about half the radiation coming in from the Sun
(short-wave visible radiation) is absorbed at the Earth's surface; of the remainder,
30% is reflected back (by clouds, by the Earth's surface by scattering back into
space by the air itself), and 20% is absorbed in the atmosphere. Thus warmed,
the Earth reradiates much of the energy received--but in the longer-wave, infrared
range. Some of this infrared radiation escapes into space, but some of it is
absorbed by carbon dioxide and water vapour and thus heats the atmosphere. The
warmed atmosphere in turn emits more infrared radiation-some back to the
Earth and some out into space.
The delicate balance between radiation gained and radiation lost by the
atmosphere as a whole depends chiefly on the concentrations of carbon dioxide
and water vapour, but also on certain other gases which are present as pollutants
in much lower concentrations, including methane, CFCs and nitrous oxide. The
total amount of water vapour present has apparently remained constant for as
long back in time as scientists have been able to measure it; the level of carbon
dioxide, however, is a different matter.
The absorption of some of the outgoing long-wave radiation by atmospheric
gases is known as the 'greenhouse effect' because it is similar to the effect of
glass in a greenhouse retaining the Sun's warmth. This effect has kept the
temperature of the Earth stable, with a level of carbon dioxide in the atmosphere
THE WEATHER
that remained unchanged for thousands of years. However, since the Industrial
~evolutiodwe have introduced more carbon dioxide (largely from the burning of
coal, oil and gas) and other pollutant gases, so that the composition of the
atmosphere has begun to change. More outgoing radiation is being trapped, with
a consequent rise in global temperature likely.
The effects on the energy budget of geothermal sources, such as volcanoes, may
be significant, because small particles in the atmosphere, such as volcanic ash
(and particulate pollutants from industry), can block incoming solar radiation
while allowing outgoing radiation to pass into space.
AIR MASSES
A large volume of air that shows little variation in temperature and humidity is
often described as an air mass. Air masses develop when air lies over a region of
sea or land many thousands of square kilometres in area that has a fairly even
temperature and humidity. The characteristics of an air mass depend on where it
has spent the last few days or weeks. If it has been over the Equator it is warm;
if over the poles, cold; if over the sea, wet; if over the land, often dry.
The most interesting weather happens where two different air masses meet. The
two air masses do not mix together; instead a mobile boundary forms, which is
known as a front. A warm front (shown on a weather map by a line with
semicircles on-see Figure 11, on p. 29) is a boundary where the warm air is
advancing; a cold front (shown as a line with triangles on) is a boundary where
the cold air is advancing. If a warm front passes over us the temperature rises; if
a cold front passes then the temperature often falls. These frontal zones are
usually regions of bad weather--cloud and often rain.
From a forecasting point of view, the concept of air masses is in.valuable, and
once we are aware what type of weather a particular air mass brings we have a
starting-point for each forecast. We are able to predict and plot the movement of
the fronts between air masses, and hence the bad weather attached to them.
Four main air masses are responsible for most of the weather we experience in
the British Isles: Tropical Continental-warm and dry; Tropical Maritimewarm and moist; Polar Continental--cold and dry; and Polar Maritime--cold and
fairly moist.
TEACHING NOTES
It is important to reinforce the message that in any work involving sunshine,
shadows, etc., it is dangerous to look directly at the Sun. At key stage 1, to
investigate children's understanding of the Sun and its energy, ask them
questions such as:
Can they find places into which the Sun cannot reach?
What does it feel like in these places?
What do these places look like?
Why do the children think the Sun cannot reach into these places?
Can the Sun pass through our bodies? Can it pass through any other solid
objects? What about transparent ones?
The children could use drawings to show their understanding of the last group of
questions.
Encourage the children to explore how people cope with different climatic
conditions. They could begin by making a display of clothes worn in hot weather
alongside those worn in cold weather. How do we measure our temperature and
why? Ask the children:
What does it feel like when you are too hot? What about when you are too
cold?
SCIENCE FOR PRIMARY TEACHERS
How does your body know the difference?
Why is it so important to keep our bodies at the right temperature?
Get the children to make a collection of photographs and drawings of children in
seasonal clothing and encourage them to make some kind of grouping or
classification of the clothes. The question:
What kinds of shoe do you wear in cold weather?
could lead to a discussion of what the soles of different shoes are like:
Which shoes are good for gripping?
Which ones are good for sliding?
What kinds of impression do different shoes make in the snow?
Work on ways of coping with the heat and cold can provide many learning
experiences for the children and may relate to other topic areas, such as
'Materials'.
KEEPING OURSELVES WARM
Set the children some challenges: ask them to find ways of testing the warmthpreserving qualities of various articles.
Which types of shoe best keep out the cold?
Which sorts of glove are the warmest?
What do the children have on their beds to keep them warm?
How do sheets and blankets keep them warm? What about duvets?
Older children could be encouraged to think about how they might prepare for an
expedition to an area with a different type of climate. For example, ask them to
imagine that they are joining an expedition to the North Pole. As part of the
preparations they must investigate which types of fabric are most effective in
keeping out the cold.
North Pole challenge
You could begin by discussing with, the group or class the type of weather they
will encounter and what sorts of factors they will need to consider.
Make a note of any relevant vocabulary used by the children themselves, and be
prepared to introduce technical vocabulary such as 'thermal', 'insulation',
'conduction', 'temperature' and 'thermometer'. Make sure the children understand
the words and use them in display work.
Allow each group time to look at the fabrics they have chosen to investigate.
Discuss how the materials are manufactured, and their possible properties. The
children could observe them closely using magnifiers. Finally, they could predict
which fabrics they think would be best at keeping out the cold.
The children will now need to devise investigations to test their predictions. Just
how fair their tests will be will depend upon their previous experience and level
of expertise. Be prepared to offer concrete advice in terms of resources available
and ways out of frustrating situations, but keep your suggestions as open-ended
as possible, for example:
Is there any way you could measure the temperature?
How much material should you use?
_
THE WEATHER
One group may decide that a warm drink could be used to represent a human
body. They may consider testing six different materials by wrapping them around
six different beakers containing hot orange juice at a known temperature. The
insulated beakers could be placed in a freezer or in a box lined with polythene and
filled with a layer of ice-cubes. The temperature of the orange juice could then be
taken at regular intervals, or simply after 15 minutes.
Each group will eventually find their preferred material, and after discussion new
investigations could be followed:
Are one, two, three or four layers of the material best for keeping warm?
Consider the cost of the material measured against its effectiveness. Is
another material almost as effective but much cheaper?
How easy is it to work with the material, for example to cut or join it?
How well does the material wash? How well does it wear? How important
do you think this would be on an expedition?
COPING WITH THE SUN'S HEAT
How do we keep cool in summer? How do we make ourselves sunproof? A good
starting-point with younger children is to look at how animals keep cool.
Children who have pets at home can be encouraged to look at how they avoid
becoming overheated.
The need for people to make themselves sunproof is very important. Ask the
children to suggest ways in which they could protect themselves from the heat of
the Sun, for example by:
sitting in the shade of a tree
sitting under a parasol
wearing a hat
wearing loose clothing
wearing lightweight fabrics
using sun-filter creams.
Once the need to keep cool has been established, the children can start devising
tests to see how effective their suggestions are.
INVESTIGATION 1 : TESTING HATS
Gather together a collection of hats and get the children to sort them
according to their properties: for example, whether they are waterproof, thick,
heavy, lightweight, large, tight.
Which hat would provide the best protection against the Sun? Let the
children try on a variety of hats in small groups to determine which hats keep
their heads coolest, which give them shade, and which give them shade over
the greatest area of their body. (CAUTION-On a hygiene note, make sure
there are no cases of head-lice in your class before starting this activity !)
Ask the children what they think will happen:
if they place an ice-cube on a saucer outside on a sunny day
if they put an ice-cube under each of the hats.
On a sunny day, ask them to take outside six different hats, and under each
hat place an ice-cube on a saucer. Next to them place an ice-cube on a
seventh saucer but do not cover it with a hat. Encourage the children to think
about why you have done this.
SCIENCE FOR PRIMARY TEACHERS
seventh saucer but do not cover it with a hat. Encourage the children to think
about why you have done this.
Check all the ice-cubes frequently to see which hat keeps its ice-cube from
melting for the longest period of time.
Place the hats in order from the one that gave the most protection to its icecube to the one that gave the least.
Ask the children to design and make a sunproof hat, choosing their own
materials. Test the hats, using ice-cubes. Older children can check the
temperature under the hats. Can the children improve the test?
The children can compare the hats they have made, asking themselves why
some worked better than others.
Children can investigate other types of clothing, such as tops, shorts, socks and
shoes. Collect a variety of different tops and examine each to see which types of
clothing provide the most protection against the Sun. When comparing the
properties of different garments, younger children will be satisfied with touching
them, predicting their effects, and then wearing them. Older children can devise
tests.
For any of these activities, there will be an appropriate time for you to ask the
children to describe the degree of 'hotness' or 'coldness' in a quantitative way. To
do this will involve them in measuring; the most commonly used instrument to
measure temperature is the thermometer.
MEASURING TEMPERATURE
The temperature of the air is a good first choice to begin measuring weather
elements. Air temperature can be measured using a thermometer. Two types of
thermometer are readily available. The most common is the liquid-in-glass type,
in which the liquid (mercury or alcohol) in the bulb expands with increasing
temperature and pushes a column of the liquid up a narrow (capillary) tube to a
height that depends on the temperature. The temperature can then be read off a
graduated scale alongside the narrow tube. The second type incorporates a
bimetallic strip, which works on the principle that two different metals expand
by different amounts for a given temperature change. The strip tries to curl and
uncurl as the temperature changes, making a pointer move over a circular scale.
Both types of thermometer are acceptable, but the alcohol-in-glass type is
preferable, as mercury thermometers are not recommended for use in primary
schools. They are no more expensive than the bimetallic strip thermometers and
are usually more accurate. The scale should be as open and clear as possible, with
a graduation mark for each whole degree only, and every 10 degrees labelled. The
temperature scale should be Celsius only; it is a much more logical one to
explain (0 and 100 seem more natural to adopt as freezing- and boiling-points of
water than the Fahrenheit values of 32 and 212) and temperature readings of
below zero in winter (which will not often happen in the UK with the Fahrenheit
scale) form a good introduction to negative numbers. The temperature should be
read to the nearest whole degree at first; half degrees will.come later. Readings to
one-tenth of a degree are not necessary for keeping weather records.
If you want to record true daily temperature extremes (and this is recommended),
then a maximum and minimum thermometer (colloquially termed a 'max-rnin'
thermometer) is needed; this will also serve as an ordinary thermometer. Again,
there are two types available: liquid-in-glass and bimetallic. This time the
maximum and minimum pointers of the bimetallic type are easier to read, but
the liquid-in-glass type-known as Six's thermometer-is easier to obtain. Six's
thermometer consists of a U-shaped glass tube that contains mercury and alcohol.
.Two little markers are moved up and down each branch of the thermometer tube
by the mercury column, which is itself moved by the expansion and contraction
of alcohol. As the temperature rises and falls, the markers are left behind as a
record of the maximum and minimum temperatures reached. The reading can be
THE WEATHER
taken at any time, and the markers reset afterwards, either magnetically or by
tilting. (CAUTION-If you decide to use Six's thermometer, make sure that the
children have access to it only in the presence of a responsible adult.)
It is interesting to compare air temperatures with soil temperatures, since, as we
shall see shortly, many weather phenomena are caused by a difference in air and
surface temperatures. The temperature of the soil, at a depth of about 10 cm, can
be measured easily with a relatively cheap soil thermometer. The range of
temperatures in soil is much less than in air, both over the course of a day and
through the year, and the maximum and minimum temperatures will occur at
different times to those of the air. You may find it useful to record soil
temperature when involved in work on plant growth.
Where should the thermometer be put?
The only hard and fast rule is that the thermometer must be out of direct sunlight
so that it reads the temperature of the air, and not the temperature to which it has
itself been heated by direct light from the Sun. Meteorologists measure air
temperature with a thermometer housed in a Stevenson screen, a standard-sized
white-painted box that stands 1.2 m above the ground. The white paint reflects
most of the Sun's heat, and the box 'has louvred sides to allow air to blow
through. You could make your own using manufactured louvred panels; for a less
sophisticated version, try placing the thermometer in a white-painted box that
has a door but no base, or even in a short section of white PVC drainpipe. If this
sort of construction work is not feasible, then hanging the thermometer on a
north-facing wall is an acceptable alternative.
The daily maximum air temperature occurs at about 1400 hours GMT (use the
24-hour clock for recording all measurements). In winter the temperature early in
the school day (that is, at about 0900 hours) will not be very different from the
overnight minimum. These are both good times, therefore, to take readings if
you intend to make regular observations over a few weeks and record the results.
One of the problems in using most types of thermometer is getting the children
to read them accurately. Several manufacturers have now produced thermometers
with digital readouts, which makes this easier.
/
SIMPLE THERMOMETER WORK
The classroom is a convenient place in which to start investigations relating to
measuring and recording temperature. Some simple activities using thermometers
are given below.
Take a series of readings to find out whether the indoor temperature varies
during the day.
Are temperature readings affected by the position of the thermometer? Try
placing it at floor, shoulder and ceiling heights to find out whether the
thermometer shows the same temperature at different heights.
What is the temperature outside? Is it the same in the shade as in sunlight?
Investigate how a greenhouse works. Lay two thermometers on a small tray
of soil, and cover one with an clear, transparent plastic cover-the cover of a
small plant propagator would be ideal, but you could also use any clear
plastic food container. After a set time, look at the readings on both
thermometers. Does the temperature of the two thermometers vary? Does it
make any difference if the cover is coloured rather than clear?
Ask children to predict which colours they think would be more comfortable
to wear in hot weather. Get them to wrap two identical thermometers in
separate pieces of dark- and light-coloured material; they will discover that
the darker sample gets hotter because it absorbs more of the Sun's rays.
Having had some experience of using a thermometer, the children could gain a
better understanding of how it works by making their own simple thermometer.
.
SCIENCE FOR PRIMARY TEACHERS
INVESTIGATION 2: MAKING A THERMOMETER
Fill a plastic soft-drink bottle (or similar container) with water to which a
few drops of red food colouring have been added. This will serve as the bulb
of the thermometer.
Next, insert a thin plastic tube into a watertight cork or Plasticine stopper
that has a small central hole. (CAUTION--Care is needed for this. The job is
made easier if the end of the tube is lubricated with washing-up liquid.)
Once the stopper is pushed into the bottle, the liquid will rise slightly up the
tube. Cut two slits in a sheet of paper so that it can be threaded over the tube
to make it easier to see the level of the liquid. (Figure 13 in the Study
Commentary for Unit 9 shows a similar set-up.)
Leave the bottle for an hour or so to reach room temperature, and mark the
level on the paper scale.
The children can now place the thermometer into a bucket containing ice-cold
water and then into one containing hot water to see what happens.
The new levels of the liquid could be marked on the paper to provide a crude
scale. Encourage the children to notice what happens when the bottle is
placed into hotlcold water? Can they suggest any reasons for this?
KEY POINTS
The Earth is surrounded by a mixture of gases called the atmosphere, which
provides the air that we breathe, insulates us from excessive heating and
cooling and filters out harmful radiation from the Sun.
Only about half the radiation coming in from the Sun (short-wave radiation)
reaches the Earth's surface to be absorbed.
The Earth emits its energy as long-wave radiation: only 6% of outgoing
radiation escapes directly to space.
The tendency of the atmosphere to prevent long-wave radiation escaping is
called the greenhouse effect.
The increase in the amount of,carbon dioxide and other pollutant gases from
industrial processes is trapping more long-wave radiation, producing a rise in
global temperatures.
WATER IN THE ATMOSPHERE
L
a
n
d
Main attainment target and levels addressed in Section 3: AT9: levels 1, 2,
5
STUDY NOTES
Water exists in the atmosphere in three forms: as water vapour, liquid water
drops (in clouds, fog and rain) and ice (in very cold clouds, as ice crystals,
hailstones and snowflakes). The amount of water vapour in the air is known as
its humidity-how damp or moist it is. Water changes from one form to another
by evaporation, condensation, freezing, melting and subliming. This is shown
diagrammatically in Figure l. (Sublimation is the direct change of ice into water
vapour without passing through the liquid state, which can occur in very" dry but
cold conditions.)
THE WEATHER
subliming
FIGURE 1 Water can change from one form to another.
HUMIDITY
Evaporation of water is taking place all around us: from lakes and rivers, from
wet vegetation and soil and, of course, from the oceans. Consequently air always
has some water vapour in it. However, the amount of water vapour the air can
hold is limited; when it is holding as much as it possibly can we call it
saturated. The amount of water vapour it takes to saturate the air depends on its
temperature; air at 30 "C (a hot summer day) can hold about 25 g in every
kilogram (about one cubic metre), whereas air at 0 "C (a frosty winter morning)
can hold only about 3 g in every kilogram.
If warm air containing a lot of water vapour is cooled, then sooner or later it
finds itself saturated; the temperature at which this occurs is known as the dew
point of the air. Any further slight cooling of the air will mean that the air can
no longer hold all its water as vapour and some of it must condense into water
droplets. This is exactly the process that forms fog and cloud; moist air is cooled
below its dew point and fine droplets are created. At the ground, these droplets are
deposited as dew-hence the name dew point.
We can see condensation in progress when we breathe out on a cold winter day;
our warm, moist breath is cooled below its dew point as it mixes with cold air,
and a fine fog forms every time we speak. On a hot summer day, water droplets
will condense on to the outside of a glass of cold lemonade, as the air coming
into contact with it is cooled below its dew point.
We use the term relative humidity (often abbreviated to r.h.) to describe how
damp air is. Relative humidity refers to the amount of water vapour in the air,
expressed as a percentage of the amount of water vapour that could be held by the
air at that temperature.
At the dew point of the air the relative humidity is, of course, 100%. In Britain
100% relative humidity is quite common, as fog frequently shows us. Values
below 30% relative humidity occur quite rarely and tend to come with spring or
summer south-easterly winds.
Measuring humidity
Weather stations use two thermometers to measure humidity: one ordinary
thermometer and one with its bulb kept wet by being encased in a muslin sleeve
dipped in a water reservoir (Figure 2). The two thermometers placed together are
called a wet-and-dry-bulb hygrometer. Water is evaporated from the sleeve by air
passing over the wet bulb; the heat energy used up to effect this change results in
the temperature of the wet-bulb thermometer being lower than that of the drybulb thermometer. (You can demonstrate this cooling effect by wetting your
finger and blowing on it.) The relative humidity can be found by noting the
SCIENCE FOR PRIMARY TEACHERS
difference between the temperatures of the wet and the dry bulbs, and using a set
of tables to establish the exact relative humidity value. The moister the air, the
less evaporation takes place and the smaller is the difference between wet- and
dry-bulb temperatures. This is the reason why a very humid day in summer feels
so hot: evaporation of sweat from your skin is reduced in humid conditions, so
that the cooling effect of the evaporation is reduced compared with that on less
humid days, even if the air temperature is the same.
muslin sleeve
purified water
FIGURE 2 A wet-and-dry-bulb hygrometer.
FOG
On a clear night the temperature of the Earth's surface falls quickly, because there
are no clouds to trap and reflect back the radiation from the surface. If there is no
wind, then the relatively warmer air on contact with the cold surface will be
cooled below its dew point and dew will be deposited on the surface (as on a
glass of lemonade on a hot day). If there is a slight wind, then it will mix up the
air to a height of several metres, or perhaps several tens of metres, above the
ground and cool all of it below its dew point; thus a fog will be formed. The fog
may be a very shallow one, lying across a meadow around the legs of cows, or it
may be a deep one, covering tall buildings.
If the wind is very strong, then air is mixed up to such a great height that the
cooling is spread over a large mass of air, and none of it falls below the dew
point; in windy conditions, therefore, fog does not form.
Another common way in which fog forms, particularly near the coast, is as a
result of warm, moist air blowing over a cool surface. This happens when wind
THE WEATHER
blows moist, relatively warm air over a cool sea; then a sea fog will form along
the coast.
On high ground we sometimes encounter hill fog; this is really a case of the hill
being high enough to be in cloud.
The distance at which objects can be made out is known as visibility. On a very
clear day we can see 30 or 40 km; when it is misty this will be reduced to a few
kilometres, and when the visibility falls below 1 km we have (by definition) a
fog (Figure 3).
TV mast
I
10km
lkm
FIGURE 3 Visibility distance gives the definition of fog. (a) Visibility of more
than 10 km. (b) Visibility of about 1 km.
Fog can inconvenience and sometimes endanger lives. The official definition of
fog as a visibility below l km is sensible for aviation purposes but for the
general public and the motorist an upper limit of 200 m is more realistic. Severe
disruption of transport occurs when the visibility falls below 50 m.
Measuring visibility
Visibility is measured at an official weather station by reference to a number of
known landmarks at many different distances. A simplified version of this
system, using two or three landmarks at distances of, say, loom, l km and
10 km, will allow the visibility to be described as 'fog', 'poor visibility' and
'good visibility', respectively.
Freezing fog is composed of supercooled water,droplets. These occur when very
pure water is cooled to well below 0 "C. Because it is very pure it is able to
remain in the liquid state. The supercooled droplets are deposited on to surfaces
such as lamp-posts and fence-poles where they freeze to form feathery crystals of
ice called rime.Freezing fog presents a serious problem for the electricity and
broadcasting industries, whose pylons, overhead wires and masts can become
covered in it. The mass of ice on a mast, for example, may increase dramatically
as the supercooled water droplets cover every exposed surface with a coating of
rime. For example, the Emley Moor transmitting mast on the Pennines
collapsed under such conditions.
SCIENCE FOR PRIMARY TEACHERS
CLOUDS
Clouds, like fog, are made up of millions of tiny droplets of water or particles of
ice. In size the water droplets vary between one-tenth and one-hundredth of a
millimetre in diameter, and there may be between one million and one billion
(one thousand million) droplets in each cubic metre of air. As with fog, the water
droplets form when air is cooled below its dew point and condensation occurs. In
the case of clouds this happens because the air rises.
Air will rise for two different reasons: either because of convection as a result of
warming at the Earth's surface, or because it is forced to rise in frontal systems
or as it passes over higher land. As it rises, air has to expand in order to equalize
its pressure with the air at the higher level. This expansion results in cooling.
Clouds formed when air rises as a result of convection
On a sunny day the sunshine will heat the ground, and this in turn will heat the
air adjacent to it (Figure 4). This warmer air is less dense than the cooler air
above it, and so it will rise naturally, often in strong localized upcurrents called
thermals. (Glider pilots use thermals to gain height.)
thermal
condensation
level
cumulus cloud
t
t
t
t
t
t
t
hot air rising
ground heated by Sun
FIGURE 4 Development of clouds as a result of warming at the Earth's surface.
When the air in the thermals has risen sufficiently to cool below its dew point,
then water droplets will condense out and a cloud will form. The height at which
this starts to happen is called the condensation level. Because of the bubbling-up
of these thermals, the cloud, too, will look bubbly-this type of cloud is called
cumulus. Small cumulus clouds formed in thermals are common on a summer's
day and look like bits of cotton wool in the sky.
If the thermals are very strong (because the sunshine is very strong, or because
the air is very cold) then these cumulus clouds will bubble up to form dark,
towering cumulonimbus clouds. We often get rain (in showers, rather than for
lengthy periods) from these clouds, and sometimes thunder and lightning.
Clouds formed when air is forced to rise
Air can be forced to rise for one of two main reasons. First, when air meets a
range of mountains or hills it has to rise to get over them. Secondly, near lowpressure areas (depressions-described in Section 4) and along fronts there is a
general slow ascent of air. In all these cases air will rise and clouds will spread
THE WEATHER
out to form a featureless layer called stratus cloud. In hilly regions the hilltops
may be above the cloud base; this gives what is generally termed hill fog.
Quite often it rains from stratus clouds, but the rain is usually a light drizzle. If
the stratus becomes very thick, it looks black from the ground, and quite heavy
rain can fall; the cloud is then called nimbostratus.
Part-cumulus and part-stratus clouds
Sometimes cumulus clouds, instead of being bubbly, spread out into more of a
layer. At other times stratus clouds, instead of being completely featureless,
break up into cells. In both cases the result is a cloud called stratocumulus; part
stratus and part cumulus. It is a very common cloud over Britain.
High clouds
All the clouds we have mentioned so far are mainly composed of water droplets.
As we have seen, even though the temperature of a cloud may be well below
0 'C, water can still exist as a liquid-that is, as supercooled water droplets.
However, right at the top of the troposphere are clouds made of ice crystals.
Sometimes these clouds are in the form of wispy feathers or streaks across the
sky; these are cinus clouds. Sometimes the ice crystals form a complete but very
thin veil of cloud, through which the Sun can be clearly seen, occasionally with
a halo around it; this is cirrostratus cloud. These two types of cloud are often
most evident near sunset, when they can be brilliantly illuminated.
Classifying clouds
A weather observer has to know the names and appearance of all these types of
cloud, but this takes a lot of practice and experience. Classification of cloud type
can be as simple or as complicated as you want. Illustrations of the ten basic
types of cloud can be found in several books, and the BP Cloud Charts are an
excellent source of clear pictures (see the Resources Section for details). At the
very least, it is worth learning the difference between the flat, stratus-type clouds
and the bubbly, cumulus type cloud, as well as the distinction between low and
high-level clouds.
Cloud cover as well as type is observed and recorded. Conventionally cloud
amount is measured in eighths (or oktas). This is rather too detailed for everyday
use, and using four states of sky is sufficient: for example, clear, partly cloudy
(that is, less than half the sky covered by clouds), mainly cloudy and completely
cloudy. You will probably be surprised at how often it is completely cloudy and
how seldom it is completely clear!
Why do clouds 'float'?
Natural clouds contain vast amounts of water-many thousand of tonnes. So
how are they able to 'float' in the air? Water thrown up from a bucket into the
air does not drift away in the form of a cloud; it soon falls back to the ground.
Clouds.are buoyant because they generally form in air that is gently (sometimes
rapidly) rising, and the droplets of water of which they are composed are so tiny
that their fall-speed is less than the upcurrents of the surrounding air; therefore
the cload 'floats'.
Weak upcurrents (a few centimetres per second) are found in stratus-type clouds,
but they often extend over vast areas of thousands of square kilometres. These
produce drizzle, characteristic of mild, dull weather.
The most powerful currents of rising air-up to a few metres per second-are
found in cumulonimbus (storm) clouds. These occur only over a relatively small
region (say, a few kilometres across), but the drops in this type of cloud are able
to grow very large.
SCIENCE FOR PRIMARY TEACHERS
Thunder and lightning
I
Lightning occurs when static electricity builds up within a cloud. A difference in
charge then exists between that region of the cloud and the ground, or between
that cloud and a nearby cloud (Figure 5). The electrical charge is thought to build
up on ice particles or on water droplets. If the difference in potential becomes
sufficiently great an electrical discharge occurs-that is, a very large spark jumps
the gap. Intense heating along the discharge path causes very rapid expansion of
air and this explosive expansion is heard as thunder.
FIGURE 5 Lightning jumps from place to place within the cloud and from cloud to
ground.
We see the lightning immediately, but because the thunder travels at the speed of
sound (half the speed of Concorde!), there is a slight delay before we hear it. We
can use this delay to estimate the distance of the lightning strike: every three
seconds between the lightning and the thunder represents a distance of
approximately one kilometre.
PRECIPITATION
Precipitation is the return of water from clouds to the Earth's surface as part of
the water cycle (Figure 6 ) . Rain, snow, sleet and hail, are all forms of
precipitation.
THE WEATHER
condensation
precipitation
e.g. rainfa-
11111
/ / /
/
evaporation
FIGURE 6 The water cycle.
How is rain formed?
Everybody knows that rain comes from clouds, but not all clouds give rain. To
understand how rain is generated, we first have to look closely at a cloud. We
have seen that clouds are formed when water that evaporates from the s~irfaceof
the Earth rises (as water vapour) and cools to a temperature at which it condenses
back to liquid again in the form of water droplets. A water droplet can form only
when it finds something to condense on to-this is usually a very small particle
of dust, ash or sea-salt. There can be up to one billion water droplets in each
cubic metre of cloud.
Within a cloud, the larger droplets 'fall' through the ascending air more rapidly
than the smaller ones, and in doing so they tend to gather up the smaller droplets
and grow larger themselves. This process is called coalescence. Eventually the
larger drops grow heavy enough to fall to the ground (in spite of the upcurrent of
air) as rain. However, much of the rain that falls on the UK originates from a
different process in cloud, which leads to the formation of ice crystals. The ice
crystals melt as they fall to the ground.
The smallest raindrops are about half a millimetre in diameter, but large drops in
showers can be up to several millimetres across. A rainfall rate of 0.5 mm per
hour (steady rainfall) may consist of 250 raindrops of typically 1 mm diameter in
each cubic metre.
Water vapour in weak upcurrents condenses at a lower rate, and this produces
smaller droplets, of less than 0.5 mm in diameter, which fall as the fine rain
known as drizzle. Although it can be persistent, drizzle hardly ever gives large
amounts of rainfall, because the drops are so small and fall so slowly.
The largest droplets are produced by cumulonimbus clouds, and when they
eventually fall they do so as a heavy shower.
Incidentally, a good place to view raindrops is through the windscreen of a car.
Measuring rainfall
Rainfall is measured as the depth of water which would accumulate on a level
ground surface if it were prevented from running away. Rain-gauges are used to
measure rainfall, and there are many different types available; the more expensive
will provide a measuring cylinder. Rain-gauges can be placed anywhere as long
as they are more than 5-10m from a building; because the amount of water
collected can be affected by the presence of trees or buildings, the more open the
site the better.
SCIENCE FOR PRIMARY TEACHERS
Just about any container can be used to collect rain, however. The amount of rain
collected can be measured simply by dipping a stick into the water and measuring
to what depth it is wetted-in millimetres. Whilst this is a very simple (and free)
method, it does have one disadvantage, which can be overcome by using a
slightly more sophisticated design. Depths of a millimetre or two are difficult to
measure, so, by using a water storage container with a collecting funnel of a
larger diameter, the depth of water collected will be correspondingly increased.
Nothing is more disappointing-after an apparent downpour than to find only a
few millimetres of water at the bottom of a container. A 75 cm2 funnel (of about
5 cm radius) feeding a 12cm2container (of about 2cm radius) will give a depth
of water of about 6 mm in the container for every 1 mm of rain on the ground.
(This observation could form a useful introduction to work on area and volume.)
A plastic funnel inserted into the top of a small soft-drink bottle would be
suitable; to prevent spillage, bury a largish tin can (for example of the sort that
ground coffee is often sold in) lOcm or so in the ground, and put the bottle into
this with the collecting funnel above the ground. (CAUTION-Make sure that
there are no sharp edges on the tin.)
Transfer daily collections of rain to clear tubes. Mounting these on a suitable
board will give you a very simple bar chart. However, for a more permanent
record of rainfall transfer this information into a record book or store it on a
computer program.
How often and how much does it rain?
Because rain always seems to come when we least want it, we tend to think that
it rains often in Britain. However, most clouds produce no rain at all, and over
south-east England rain falls in only about 500 hours through the year, or about
one hour in 17. Even in very wet parts of the north and west of Britain, although
there may be ten times the rainfall, it still only rains one hour in seven.
The average amount of rain over the UK varies from less than 600 mm per year
in eastern England to over 2 000 mm in the north-west of Scotland.
Rain and our lives
Rain is a vital part of our lives; without it we could not exist. We need rain to
fill streams, rivers and reservoirs so that there is a regular supply of drinking
water. Rain supplies water to enable crops to grow, and the grass to feed cattle.
During the summer of 1976 there was a long drought throughout the south of
England; water was rationed, many crops failed and the dry conditions led to
forest fires. In 1990 similar drought conditions occurred, but for most of us there
was no water rationing. Far worse are the effects in some parts of Africa, where
the failure of the 'rainy season' to arrive results in starvation on a terrible scale.
Scenes of famine in Ethiopia and the Sudan are harrowing testimony to our need
for rain.
Rain can also bring problems, especially if a great amount falls in a short space
of time. It may wash away the thin topsoil and make farming difficult. It may
also cause serious flooding if the rivers cannot carry it away fast enough and
burst their banks, thus inundating farms and towns.
Snow and sleet
Most clouds, especially at our latitudes, are composed of water droplets and ice
particles side by side. In calm conditions and temperatures well below freezingpoint, the ice particles grow into hexagonal crystals that collide with one another
within the cloud to form snowflakes (Figure 7), which then fall from the cloud
base. No two snowflakes are exactly alike.
If the air is cold enough (below about 4 "C at the surface) the snowflake will
reach the ground, but if the air is warmer it will melt on the way down and reach
the ground as a raindrop. So even in summer, the chances are that the torrential
THE WEATHER
downpour that may be ruining Wimbledon or the Test Match will have started its
life as a mass of descending snowflakes within the shower cloud. Sometimes a
snowflake will not have completely melted before it reaches the ground; it will
be part snow and part rain. This is called sleet.
FIGURE 7 Snowflakes.
Hail
Hail falls from cumulonimbus clouds; these are made up of water drops and ice
particles, and a hailstone in fact starts life as an ice particle. The particles build
up into ice crystals by the processes of condensation and freezing. The ice
crystals are blown up and down inside the cloud by strong air currents. As they
are thrown about, the cloud drops freeze on to the ice crystals in layers, like the
skins of an onion. When they freeze near the warmer, lower part of the cloud
they freeze slowly, and the layer appears as clear ice. Near to the higher, colder
part of the cloud the drops freeze instantly, resulting in a layer of opaque ice
(Figure 8). By counting the layers of ice in a hailstone we can tell how many
times it was blown up and down inside the cloud.
Uclear ice
FIGURE 8 The formation of a hailstone. (a) The path a hailstone takes as it forms.
(b) Section through a hailstone.
SCIENCE FOR PRIMARY TEACHERS
Hailstones vary greatly in size: the more violent the air currents, the taller the
cloud will grow, and the bigger the hailstones are likely to be. Most hailstones
are between 5 and 50mm, but they can be much larger, sometimes being large
enough to cause damage to car windscreens and greenhouses, and injury or even
death to people.
TEACHING NOTES
In these notes we have placed the emphasis on rain since it is our most common
form of precipitation. However, the activities suggested could easily be adapted
to explore such weather phenomena as snow and hail. For example, the depth of
snow can be quite easily measured with a ruler, preferably in a place where it has
not drifted. Bringing, say, a beaker full of snow indoors and melting it will show
the large difference between the depth of the snow and the amount of rainfall to
which this corresponds.
At key stage 1 children can start to explore what rain is and make observations
about it. Going out to 'experience' the rain has to be done with care ... a
cloakroom full of sodden clothing is not pleasant. It is nevertheless important to
go out, or be as near to the rain as possible. Get the children to look at and listen
to what is happening, and to think about the following:
What does the rain look like? Does it have a colour?
Does rain have a smell or a taste?
If they close their eyes, can they 'hear' rain?
What does the rain feel like on their hands?
Can they see from which direction the rain is coming?
Other work outside could include getting the children to watch the rain on the
ground to see where the rainwater goes to. Is there a gully or dip in the ground?
Can they see a drainpipe or a gutter? Get the children to collect some rain in their
hands and look at it before it trickles away.
Can the children think of a way of making the water go where they want it to?
Get them to try using cardboard tubing, plastic sheeting or pieces of guttering to
make channels to a shallow bowl, bucket or margarine tub sunk into the ground.
Back in the classroom, children could depict a cloudburst using a piece of grey
cloth cut in the shape of a cloud, with raindrops cut from thin, transparent plastic
hanging from the cloth by cotton threads. The cotton threads can be stuck on to
the cloth using transparent sticky tape. They could make paintings of themselves
dressed in their rainy-day clothing and spatter raindrops on the picture using
combs dipped in grey paint.
Why do the children think houses in Britain have sloping roofs? If you are able
to get hold of some tiles, get the children to pour water over them to see the
effect. Are the shapes of roofs the same in other countries?
Why do we use umbrellas? Make a collection of umbrellas, look at the opening
movement, count the spokes and see if they all work in the same way. Outside,
on a fine day (!), test the different umbrellas with a child-sized watering can filled
with some water. Where does most of the water run down? If a child sits
underneath will he or she get wet? What does the 'rain' sound like underneath the
umbrella? Does the real rain sound the same?
Encourage the children to think about the type of clothing they wear when it is
raining. Work on the properties of different fabrics could lead to investigations to
find out how much water different materials absorb. The children could set up an
investigation involving either pieces of fabric or articles of clothing made of
different materials (you could use dolls' clothing) to see how the materials
change if left out in the rain. Encourage them to set up a hypothesis about the
absorbency qualities of the different fabrics and test it fairly.
THE WEATHER
The way in which fabrics dry out after they have been in the rain can lead to
additional investigative work. Questions on drying out could include:
Does it make any difference to the time taken for a wet fabric to dry out if
the fabric is screwed up, folded or left flat?
Do the positions of the samples of fabric (for example in different places
about the classroom or outside the school building) make any difference to
the time taken for a sample to dry out?
How does the weather affect the time taken for fabrics placed outside to dry?
Does it affect fabrics drying inside?
Which fabrics take longest to dry? (Discuss the need for a fair test by using
pieces of fabric of the same size placed in similar conditions.)
Are there ideal weather conditions for drying clothes? (Ask the children to
seek the opinions of relatives who do the washing.)
In discussions on rain and weather conditions, children can talk about the need to
keep dry in terms of everyday events. What would happen if we always got wet?
How can we prevent ourselves getting wet in the rain? Using a variety of
materials, encourage the children to observe their properties and ask them to
predict which fabrics they think will keep us dry in the rain.
The idea of an object being waterproof can be explored with the very youngest
children, and suitable problem-solving activities can be found for different ages
and abilities, perhaps initially in connection with fabrics. A number of different
problem-solving exercises can be set up. For example:
Sooty needs a rainhat. Can you help him to choose the best materials from
which to make one?
Rebecca is going on holiday. How can she make a waterproof tent?
What is the best fabric for covering a pram?
Err01 needs a new raincoat. Which type of fabric should he choose?
Get the children to imagine that they have been asked, as members of a polar
expedition, to research, design and make an all-weather back-pack.
The aim of exercises such as these is to discover which of a range of materials is
waterproof and which is the most suitable for a particular purpose. The children
will undoubtedly discover that a continuum exists, ranging from materials that
are totally absorbent (for example a sponge) to those that are totally waterproof
(such as polythene). It may be useful to ask the children to grade their materials
on this continuum.
Valuable experiences relating to AT1 can be covered with such work. Help the
children to understand that their investigations should include:
predicting, and recording their predictions-which
previously gained knowledge
should be based on
devising and canying out tests
carefully observing what happens
sharing their findings.
As children move up through the school, you may wish to plan to revisit the
concept of something being waterproof many times in a context relevant to their
age and stage of development. For older children, further investigations into
.resistance to rain could include:
Can fabrics be made waterproof against the rain by treating the surface with
'safe' substances, such as petroleum jelly, zinc and castor oil, cooking oil,
olive oil, jam, wax, etc.?
As members of a polar expedition team, imagine that you have been asked
to research, design and make a waterproof shelter that will not be too heavy
to cany.
SCIENCE FOR PRIMARY TEACHERS
How rainproof is a house brick? Test the absorbency of bricks by weighing
them before and after placing them in water for a given time.
What makes a roof waterproof? Test tiles, slates and thetch (straw) to see
whether they are waterproof. Does the way in which the material is
positioned on the roof have an effect on whether or not it is waterproof?
Just how waterproof are waterproof plasters? Devise a survey of several
brands.
Cross-curricular work involving rain can be introduced at both key stage 1 and
key stage 2. Key stage 2 work on rain can be part of an ongoing weather activity
or a project theme in itself.
Keeping a record of rainfall is a useful activity. Encourage the children to think
about such factors as:
Does it make any difference where rain collectors are positioned?
Do all parts of the school playground or field receive the same amount of
rainfall?
Records of rainfall can provide children with information such as:
the wettest or driest day of the month or year
the month in which the greatest number of wet days occurred
the longest period during which no rain fell.
If members of the class have pen friends in other areas, or countries, they may
find it interesting to exchange weather records for similar periods of time. How
could they make sure that this is a fair comparison?
Rain is one of the most important elements of the weather. As well as being
vital for crops to grow, it fills the reservoirs that supply water for drinking,
washing and other domestic uses. Industry also uses millions of litres of water
every day in processes as diverse as food production and the manufacture of
electricity. An enlightening activity is to estimate how much water an average
family uses on a daily basis! Visits to museums can often help here.
To understand how rain is formed, children will need to understand the processes
of evaporation and condensation and their role in the water cycle. Activities
involving these processes are included in the Study Commentary for Unit 27 and
are appropriate only for older children.
However, even at key stage 1 it is not too early to ask the children to think of
the consequences of too little rain, as in countries where crops fail because of the
lack of water, or too much, as in flood areas. Indeed, in Britain we have
experienced both extremes in the last few years.
What do the children think we can do to help drought or flood victims?
Dramatizing different points of view can help them to understand some of the
complex factors involved. Older children could voice the feelings of a group of
people who need water and so wish to dam a river valley to make a reservoir, yet
also need the land for their crops. This type of debate will inevitably lead to a
discussion of the relationship between the quantity of water needed to grow
sufficient food, and work could continue on the different food crops grown in
different parts of the world. Try to encourage children to become aware of
different weather situations, and have a real appreciation of the importance that
the weather has in all our lives.
KEY POINTS
Water is present in the air not only as a liquid (water droplets) and, in high
clouds, as a solid (ice crystals), but also as an invisible gas-water vapour.
Water changes from one form to another by evaporation, condensation,
freezing, melting and subliming.
THE WEATHER
Relative humidity is a measure of the amount of water vapour in the air.
Humidity depends mainly on the temperature of the air: warm air can hold
more water vapour than can cold air.
Clouds are made of millions of tiny, very light drops of water or particles of
ice. They form when air is cooled below its dew point, and condensation
occurs.
Clouds are broadly classified according to their height in the sky-that
high, medium and low clouds.
is, as
Precipitation is the general term for water falling from the sky in solid or
liquid form, for example rain, snow and hail. Before the water droplets, ice
particles and ice crystals making up a cloud can fall as precipitation, they
must grow much larger and heavier. They do this by coalescing (whereby
large water droplets absorb smaller ones as they fall).
4 ATMOSPHERIC PRESSURE
Main attainment target and levels addressed in Section 4: ATY: level 3
STUDY NOTES
Air pressure, often called simply 'pressure', can be a difficult concept for us to
appreciate; unlike temperature or rainfall, we cannot see it or sense it ourselves.
However, it is really quite straightforward. The weight of air on a certain area is
what we call air pressure-and this is measured with a barometer.
We may think of air as being 'weightless', but in fact we know that the
atmosphere stretches several kilometres above us, so at sea-level there is a
substantial mass of air pressing down upon us-about one kilogram on every
square centimetre (Figure 9 overleaf'). We do not usually feel it because air
pressure is acting in every direction all around us: air inside us exerts an equal
internal pressure to balance that outside us. The only time we do become aware
of it is when air pressure changes rapidly, for example when our ears 'pop' at
take-off or landing in an aeroplane. As you will appreciate, our ears are very
sensitive at detecting slight changes in air-this is in fact how we hear (see the
Study Commentary for Unit 10).
HOW PRESSURE VARIES WITH TEMPERATURE
The density of air becomes less at higher temperatures and, as the temperature
varies from place to place, so does the pressure because the total mass of the air
column varies with density. Pressure is measured at a large number of weather
stations all around the world, and the readings are plotted on a map. Stations
having the same pressure are then joined together by a line called an isobar. The
further apart the isobars, the lighter is the wind; where they are close together the
wind is strong. If we'draw isobars at several different pressures we find that they
and
form patterns around areas of high pressure (known as highs or antic~~clones)
low pressure (lows or depressions)-you often see these patterns on weather
maps in newspapers and on television; a typical example is shown in Figure 10
(overleaf).
SCIENCE FOR PRIMARY TEACHERS
I
l
I
I
I
I
I
I
I
I
I
I
I
I
I
--
approximately 1 kg of
air in total column from
sea-level to the top of
the atmosphere
1 cm2 (at sea-level)
FIGURE 9 Air pressure.
depression
FIGURE 10 Highs and lows on a weather map.
Pressure is measured in units called millibars, the usual abbreviation for which is
mb; the World Meteorological Organization have recommended that the standard
unit of-pressure should be the hectopascal (hPa), with l hPa = l mb; but
millibars should be in general use for a long time yet. A pressure of 1000 mb
(around average) is equal to the weight of about one kilogram pressing down on
each square centimetre (or 10000 kg m-2). The pressure we measure at the
ground varies from day to day but generally (over the UK) stays between 950 mb
and 1040 mb.
Measuring pressure is important because areas of high and low pressure have
different types of weather associated with them. When there is high pressure the
weather is generally fine, with clear skies and light winds. This is because the air
spirals outwards and downwards from the upper atmosphere-the air comes from
high regions of the atmosphere which are cold. As the air descends, it warms up
and since the total amount of water in the air mass is fixed, the relative humidity
\
THE WEATHER
falls because warm air can hold more water vapour than cold air.By day this can
mean warm sunshine as the heat radiates back into space; by night the clear skies
mean a cool or cold night, sometimes with fog and frost forming.
In an area of low pressure there is usually thick cloud, often rain or snow, and
always plenty of wind. This is because the air is spiralling inwards and upwards,
carrying water vapour to cooler regions where the vapour condenses. So the air
pressure is relatively low when there is a lot of water vapour in the air, whereas
pressure is high when the air is dry. The rain belts associated with a typical
depression are shown in Figure 11.
n
isobars
i
cold front
FIGURE l l A typical depression. The diagonal shading shows areas of cloud and
rain.
Once we can identify the highs and lows on a weather map, we know not only
what the weather is like underneath them (we could do this in any case from
other observations made at weather stations) but also, from many years of
studying weather maps, how they will move and change over the next few days.
This allows us to predict where the bad (or good)
weather will be tomorrow and
the day after.
I ACTIVITY 1:
WEATHER MAPS AND FORECASTS
The whole art of weather forecasting is to identify the highs, lows and fronts
on a weather map, predict where they will be the next day on a forecast
weather map, and use this to forecast the next day's weather for different
regions.
Over a period of, say, one or two weeks, collect a series of daily weather
maps from a national newspaper. On day 1, identify the pressure areas on and
around the British Isles. Look to see the type of weather associated with these
features. For subsequent days, follow the path and development of the
pressure features and note the weather experienced in different parts of the
British Isles. How closely can you link the weather experienced with the
local pressure feature? Can you make any predictions about the type of
weather that different areas may experience from one day to the next?
<
SCIENCE FOR PRIMARY TEACHERS
By using weather maps and watching the forecast on the television, you will
become much more familiar with the different elements of weather and come to
appreciate the weather that is associated with different pressure features.
If you have been watching a high-pressure system you may have noticed that it
remains in roughly the same place-often for several days or even longer. The
relative lack of movement of high-pressure areas is common: they often stay
around for days or weeks, and in the summer give us long sunny spells of settled
weather, as in 1990 in England.
PRESSURE AT DIFFERENT HEIGHTS
We have seen that pressure varies from place to place at sea-level depending on
the temperature of a particular place. It also changes, more rapidly, but more
consistently, as we go higher up in the atmosphere (Figure 12). The reason, as
we have seen, is that pressure is merely the weight of air above us; as we go up,
there is less air above us, and so the pressure becomes less. For every lOOm we
go up (the height of a tall church or block of flats) the pressure falls by about
12 mb.
FIGURE 12 Air pressure decreases with increasing height.
If we climb a mountain, we can tell what height we have reached by looking at a
barometer-in fact there are special barometers called altimeters, which read
height directly in metres. Pilots use altimeters to tell them what height their
aircraft is flying at; they can then fly safely in cloud. (Of course, they need to
know the pressure at sea-level in order to set their altimeters; this is given to
them over the radio by the air traffic controller.)
The change of pressure with height above sea-level means that if a weather
station is on a hill or mountain, its pressure will be quite different from that
measured at a nearby station in a valley. This would make the drawing of isobars
on a weather map impossible, so all barometer readings are adjusted ('corrected')
to sea-level by adding on the weight of the section of atmosphere between the
height of the station and sea-level.
With increasing altitude the air also becomes less dense. At sea-level one cubic
metre of air has a mass of about 1.3 kg; at the top of Mount Everest, or the
height at which jet aircraft cruise, the density is only about one-third of this
(Figure 13). Think of a high pile of foam rubber; at the bottom it will be
compressed by the mass of rubber above it, so its density will be relatively high.
Halfway up the pile, however, only half the mass is compressing it, so it will be
more open and less dense. Air behaves like foam rubber. You met this concept in
S102 Units 5-6 when you were considering density in relation to the internal
structure of the Earth.
If we climb up a high mountain where the air is less dense, then the amount of
oxygen we take in with every breath is small, and we have to pant to get enough
,
-
THE WEATHER
9
sea-level
Mount
Everest
'&zsz5
Snowdon
FIGURE 13 The pressure and density of the air change with increasing altitude.
of it. Climbers on Everest use oxygen from compressed-gas cylinders to help
them. Aircraft do the same; the cabin is 'pressurized'-that is, pumped up with
air-so that we can breathe normally even when flying at a height of 10km.
This is why you cannot open windows on aircraft; all the air inside the cabin
would suddenly rush out-and you would be sucked out with it!
MEASURING ATMOSPHERIC PRESSURE
For a reasonable long-term record of pressure, the simplest and cheapest device is
the familiar aneroid barometer, of the type that hangs on many a hallway wall.
The aneroid barometer consists of a flexible metal box from which most of the
air has been removed. As atmospheric pressure increases or decreases, the box
expands or contracts and a series of levers records the changes on a dial. The
important thing to notice is whether pressure is rising or falling: a rise in
pressure may mean settled weather ahead, and a fall, unsettled weather. To avoid
the confusion of two units of measurements, stick to millibars only-paint out
or cover over the inch scale if necessary.
Because atmospheric pressure is simply the weight of the column of air above
the barometer, the precise reading on the barometer will depend on how high
your house or school is above sea-level; raising the barometer by 10m results in
a decrease of just over 1 mb. To calibrate your barometer, you will need to adjust
it to sea-level pressure; you can find this out by telephoning your nearest
'Weathercall' service. The best time to ring is just after midday; try to choose a
clear and calm day when the pressure will not be changing rapidly or varying
much from place to place.
TEACHING NOTES
The concept of pressure is too difficult for younger children to grasp. The
activities included here are suitable for key stage 2 work.
WHAT IS PRESSURE?
Before children can start to consider air pressure, they will need to develop an
understanding of what the term 'pressure' means. You may already have covered
this in earlier work involving forces or magnetism, for example (see the Study
Commentary for Unit 3). Children will need to have experienced situations in
which it is clear that pressure depends not only on the 'pressing force' but also
on the area that it presses on-that is, if a force presses on a large area, the
pressure is reduced. Examples that illustrate this are the use of snowshoes to
spread out weight over a large area (low pressure) and the damage caused to
wooden floors by stiletto heels (high pressure). ,
SCIENCE FOR PRIMARY TEACHERS
To demonstrate air pressure you may wish to do the following Investigation with
the children.
INVESTIGATION 3: DEMONSTRATING
AIR
PRESSURE
Wash out an empty 5 litre oil-can (or similar container) that has an airtight
cap. Boil 2-3 cups of water in a kettle and pour it carefully through a funnel
into the can. The steam generated by the hot water will push out much of the
air inside the can. After a minute or two, screw the cap tightly on to the can
and leave it to cool.
As the can cools, the steam inside starts to condense back into water and
leaves a space containing very little air (a partial vacuum). The air pressure
inside the can is now very low, and the much greater pressure outside the can
will start to push'the sides in quite forcefully.
To help children gain a better understanding of air pressure, encourage them to
investigate these everyday phenomena:
Consider how a rubber sucker works. What makes the sucker stay in place?
Does it work on all surfaces, and if not, why not? Which surfaces are best?
What happens if one area of the sucker is gently lifted?
How do drinking straws work? What happens if you try and suck a drink
through a straw with a hole in it? What happens if the top of the bottle
(around the straw) is sealed using Plasticine? What happens if you blow
instead of suck?
Other investigations, although not directly related to weather, will enable
children to find out more about air pressure and what it can do. Using simple
materials, the children can investigate how slow or still air exerts greater pressure
than faster-moving air.
Place a table-tennis ball into a funnel and try to blow it out. What happens?
Why? Can you think of another way to blow it out?
Suspend two table-tennis balls close together by lengths of thread, and try
blowing between them with a straw. What happens? Can you explain this?
Such activities can be used to give children a better understanding of what we
mean by air and atmospheric pressure.
KEY POINTS
Air pressure is the weight of air pressing on a certain area.
Pressure varies because of differences in temperature: as hot air rises, it cools
and the water vapour in it is .lost as rain.
Pressure systems-known as depressions (low pressure) and anticyclones
(high pressure)-give characteristic weather patterns for the British Isles.
THE WEATHER
5 WIND
I
Main attainment target and levels addressed in Section 5: AT9: levels 1
to S
STUDY NOTES
Wind is the name we give to the movement of air. Unlike pressure, it is an easy
element to detect: we can feel it on our faces, and we can see its effect on things
around us. Wind possesses two properties: speed (how fast it moves) and
direction (the directionfrom which it is blowing).
Winds are caused by differences in temperature and pressure, and so the speed and
direction of the wind is determined by the position of weather systems-the
highs and lows seen on weather maps and on satellite photographs.
Air, as wind, tries to flow directly from areas of high pressure towards areas of
lower pressure. In very simple terms, winds blow to try to equalize the pressure
between two areas: the high-pressure area (where the mass of the air above is
great) and the low-pressure area (where the mass of the air above is not so great);
the same principle is demonstrated in water flowing along a pipe that connects
two water barrels, one full and one half full, so that the water level in both
barrels becomes the same (Figure 14).
high
pressure
f
\-
FIGURE 14 Water flows to equalize the levels in the two containers.
-
The daily weather pattern determines whether Britain is favoured with warm
southerly winds or bitter north-easterlies, but local features can modify this.
Winds are stronger over hills-sometimes twice as strong as they are over lower
ground. Winds are also stronger nearer the coast because, coming off the smooth
sea, they have not been slowed down as much (by friction) as if they had
travelled over land. Even on a day when winds are very calm, sea breezes can be
generated near the coast (see Figure 15 overleaf). During the day the land warms
up more than the sea because the sea acts as a vast heat reservoir and its
temperature changes little from day to night. So air rises over the warm land, and
more air rushes in from the cooler sea to replace it-hence an onshore breeze.
This situation reverses at night, and air flows off the cooler land at sea-level.
On a smaller scale, winds will be deflected near to buildings; we can see this in a
town square or pedestrian precinct, where papers are often blown round and round
in circles (or eddies) (see Figure 16 overleaf).
SCIENCE FOR PRIMARY TEACHERS
offshore or
land breeze
l{[
rising
sinking
air
over
cool
sea
overL
warm
land
air
onshore or
sea breeze
FIGURE 15 Development of offshore and onshore breezes.
wind flow
eddies
FIGURE 16 Winds deflected near to buildings cause eddies.
The story is not quite as simple as this, however. Air moving across the surface
of the Earth is affected by the Earth's rotation; this rotation causes winds to blow
around highs and lows (Figure 17), and on the planetary scale gives the
characteristic pattern of winds shown in Figure 18. This 'bending' of the wind
direction due to the rotating Earth is known as the Coriolis effect.
/
FIGURE 17 Winds blow around high and low pressure areas.
THE WEATHER
North Pole
CCJ
north-easterl
trade winds
\
Equator
\
\
South Pole
\ trade
south-easter,!
winds
I
c
FIGURE 18 Winds around the world.
HOW THE WIND DETERMINES OUR WEATHER
The direction from which the wind blows can tell us something about the
weather it will bring (Figure 19 overleaf). In Britain, if the wind is a northerly
one, the air has come from colder regions and will therefore bring with it low
temperatures-cold in winter and cool in summer. But if the wind blows from
the south, the opposite is the case: in summer it will be hot and in winter, mild.
A wind from the west will always be moist and bring rain, because it will have
picked up moisture during its journey over the Atlantic Ocean; but as the ocean
temperature does not change much from summer to winter, then a westerly wind
will feel mild in winter and cool in summer. An easterly wind will be dry,
because it has come from the great land mass of Eurasia; in winter, when this
land mass is very cold, the easterly wind will be bitter, but in summer, when
central Europe is usually hot, then the wind, too, can be hot.
Because the weather patterns that bring the strongest winds (lows, or depressions)
generally track across the North Atlantic from America and tend to pass just to
.the north of Scotland, the north of Britain is windier than the south. Wind is
strongest in hilly areas, and in Britain this means the west of the country; the
highest number of gales occur in the north-west of Scotland. However, few of us
living further south will forget the Great Gale of 15.and 16 October 1987, which
brought drama and devastation to south-east England. Originating from the
tropical hurricane Floyd, humcane-force winds led to 19 deaths and the toppling
of at least 15 million trees.
SCIENCE FOR PRIMARY TEACHERS
NORTH WINDS
EAST WINDS (dry)
summer
mild in
winter,
hot in
summer
SOUTH WINDS
FIGURE 19 The direction from which the wind blows can tell us something about
the weather it will bring.
MEASURING WIND SPEED AND DIRECTION
The speed of the wind can be measured in a variety of units but, unfortunately,
there is no generally accepted metric unit. Weather forecasters measure wind
speed in units called knots-one knot is equivalent to one nautical mile (about
two kilometres) per hour, and it is also almost exactly half a metre per second (a
very slow walking pace).
; However, instead of using knots, we often speak of the wind force; this refers to
one of the simplest and most common ways of measuring the speed, or force, of
the wind: the Beaufort scale. The scale assigns a number to an easily observed
effect of the wind, and was developed by Admiral Beaufort in 1838. It is shown
in a simplified form in Figure 20; wind speeds above gale force (force 8) do not
often occur over land.
THE WEATHER
Force
Description
Wind speed in
knots
CALM
smoke rises straight up
less than 1
LIGHT AIR
direction of wind shown by smoke drift, but not by
wind vanes
LIGHTBREEZE
wind felt on face; leaves rustle; ordinary vane moved
by wind
GENTLE BREEZE
leaves and small twigs in constant motion; wind
extends light flag
MODERATE BREEZE
small branches are moved
FRESH BREEZE
small trees in leaf begin to sway; crested wavelets
form on inland waters
STRONG BREEZE
large branches in motion; whistling heard in
telegraph wires; umbrellas used with difficulty
NEAR GALE
whole trees in motion; inconvenience felt when
walking against wind
GALE
breaks twigs off trees; generally impedes progress
STRONG GALE
slight structural damage occurs (chimney pots and
slates removed)
STORM
seldom experienced inland; trees uprooted;
considerable structural damage occurs
VIOLENT STORM
very rarely experienced; accompanied by widespread
damage
HURRICANE
more than 64
FTGURE 20 The Beaufort scale of wind force.
To measure the wind speed more accurately we need to use an instrument called
an anemometer, of which many types are available. The most common is a cup
anemometer, in which three or four cups are blown around an axis; the rate at
which they rotate (the number of rotations per minute, for instance) is a measure
of the wind speed.
You could try making your own three-cup anemometer; the simplest method of
taking measurements using it is to count the number of times the cups go round
in a fixed period. This is made easier if one of the cups is painted in a contrasting
colour.
SCIENCE FOR PRIMARY TEACHERS
Two types of anemometer can be bought relatively cheaply. The Ventimeter
consists of a tube containing a small disc, which is blown upwards as the wind
enters a hole in the bottom of the tube; the side of the tube is marked with a
scale to show the wind speed. In the Windmeter a small ball is used instead of a
disc.
It is somewhat difficult to measure quantitatively using an anemometer. Near to
buildings eddies will cause any anemometer to behave peculiarly-for example it
may stop and start suddenly-and, even for a crude weather station this is
unsatisfactory. However, if you can raise the anemometer up above the height of
the surrounding buildings, or put it a good distance away from them, then it is
certainly possible to make sensible measurements.
More accurate hand-held anemometers (of the cup type) are commercially
available but they are expensive. Because a hand-held instrument is unlikely to
be placed iri a sufficiently open and exposed position, it is doubtful whether the
expense would be justifiable for everyday use.
The direction from which the wind blows is measured using a weather vane, or
wind vane as it is sometimes called. A wind sock also gives an indication of the
wind force-when the wind is strong the sock balloons out, but when there is
little or no wind it hangs limply. Wind socks are seen most commonly on
airfields. Wind direction is given either in terms of compass points (eight usually
suffices-that is, north-east winds blow from the north-east, for example from
Scandinavia, towards the south-west) or as degrees measured clockwise from
north. A north-east wind will be 045O, a west wind will be 270' (Figure 21).
North Pole
west wind
(270")
FIGURE 21 Measuring wind direction.
We can use a wind rose to show how often during the year the wind blows from
each of the eight compass points. Figure 22 (overleaf) shows a typical wind rose
for one month. Although the most common direction (shown by the longest
stick) is from the south-west, and this is known as the prevailing wind, winds
from this direction only blow for one-third of the time; the rest of the time the
wind comes from a range of other directions, or conditions are calm (so no
direction can be detected).
T
THE WEATHER
,
4 days
2 days
north-
10 days
south-west
south
t
FIGURE 22 Recording wind direction using a wind rose.
TEACHING NOTES
For the youngest children you may wish to confine weather studies relating to
wind to those days where the weather is interesting and can be observed at first
hand. The following ideas give suggestions for such experiences and ways of
communicating their discoveries.
WIND SPEED AND DIRECTION
Ask the children 'How strong is the wind?' and get them to think of ways they
could measure wind strength. One suggestion is to put each child's name on a
piece of A4 paper. Crumple the pieces of paper up and let the wind blow them
across the playground two or three at a time. Is the wind strong enough to blow
crumpled sugar paper or newspaper? What happens to tissue-paper pieces? Can
the children think of other ways of folding the pieces of paper to make them
blow 'better'. (Ask them to think about whether that means further or faster.)
You could use the opportunity to discuss litter blown around by the wind, and
relate it to the protection of our environment.
Ask the children if they can think of a way to find out which way the wind is
blowing. Provide long, thin scarves, long pieces of crepe paper, and balloons or
plastic shopping bags (with holes for safety) tied to a piece of string for them to
hold in the wind and see the wind direction. Get the children to look at how each
other's hair and clothes are blowing about. Where does the wind seem to be
coming from?
A version of the sort of wind sock used on airfields can be constructed from a
wire loop with a nylon stocking or a leg from a pair of tights attached. This in
turn is attached loosely by a length of string to a nail fitted to an old broom
SCIENCE FOR PRIMARY TEACHERS
handle so that the wire can turn freely. Another idea is to simply tie a plastic
shopping bag to a broom handle. Various designs of wind sock could be
investigated to find the most effective.
A weather vane can take a variety of appearances, but its basic form is a
horizontal arm with an arrow at one end and a fin at the other. The wind blows
the fin round and the arrow points to the direction the wind is coming from. The
children can design any shape of fin-a survey of local churches and houses
should reveal a wealth of designs in addition to the familiar weather cock-but do
remember that the rear section must have a larger surface area than the pointed
end to ensure that the arrow points into the wind.
The upright section of the vane, to which the arm is attached, can be made from
a piece of wooden dowel or an old knitting needle supported on a base. A stable
base could be made by drilling a hole in an air brick into which the knitting
needle could be inserted.
The vane needs to be balanced to ensure smooth rotation. This can be achieved
using Plasticine, paper clips or drawing pins to weight the end with the smaller
surface area.
Experiment with various methods of reducing friction at the point where the
rotating arm joins the fixed part. For example, rough edges could be smoothed,
or the join could be lubricated.
Recording the information
There are various ways in which the children could record information about wind
direction and speed.
The results of tests with suspended pieces of material can be given in a table
devised by the children. They could give the wind speed, or force, in terms of the
numbers in the Beaufort scale. To establish the scale on their measuring device
they will first need to look at the signs of wind force about them when the wind
is strong enough to move a particular piece of material; they should then check
these signs against the Beaufort scale. Table 1 shows how the information might
be presented.
TABLE 1 Presenting wind measurements in tabular form
Day
Wind direction
Monday
S
Tuesday, etc.
SW
Wind speed
The information could also be presented diagrammatically,using a wind rose (see
Figure 22), or perhaps entered on to a computer database using a suitable
program.
RESISTING THE WIND
When considering how an object stands up to the wind, encourage the children to
think about how the design of the object may help its wind resistance.
A wind source
In order to investigate whether materials or objects are windproof, we need a
source of wind!
Children may be able to tell you of windy places in the school. If not, let them
investigate-the possible tools that can be used to find out this information
range from a commercial anemometers to bubbles, candle smoke, wind chimes or
\
THE WEATHER
even a wet finger. Note that this source will be erratic, but realistic: windproof
objects are exposed to wind in an erratic way.
Wind sources for use in the classroom can include bicycle and balloon pumps,
which are useful for supplying a short, sharp blast of air. They are easy to direct,
safe, and may be brought in from home. A blown-up balloon, when it is held so
as to release the air, has all the benefits of a pump and lasts longer. Fans may
also be used. (CAUTION-Take care with moving parts.)
Designing something that is windproof
When the children have established an effective wind source, they can begin to
investigate what we understand by something being windproof and look at the
various designs around us that set out to protect us from weather elements,
including wind.
The children could build model houses out of straw, sticks and bricks. Which
type will stand up to the strongest winds? Ask them who can build the tallest
tower (out of, say, empty containers or building bricks) that can stand up to a
strong wind. The children should discover that their towers need to have wide
bases to withstand the wind. (You may have already dealt with this in work on
forces-see the Study Commentary for Unit 3.)
Ask the children to observe different kinds of fences, draw them and discuss why
they have been put up. They could test how fences can be strengthened against
the wind by constructing a model fence and subjecting.it to wind. Older children
could use a spring balance to measure the force needed to blow over the fence.
These observations can be related to the various ways of fixing fence-posts
recommended in do-it-yourself books.
Another investigation might begin with the question:
How are tiles placed on to a roof and why are they put on this way?
One reason- for overlapping the tiles is to provide resistance to wind. Make a
model of a sloping roof and cover it with card tiles in overlapping patterns. (The
children may have already constructed a model of a tiled roof to investigate the
effects of rain on buildings-see Section 3.) Try blowing across the roof from
various directions and notice which direction appears to have the strongest effect
on the tiles.
The wind rushes over a roof in a similar way to air racing over the top of an
aeroplane wing. This results in the pressure above the roof or wing being less
than that below it, which causes uplift: hence the tiles are lifted off. You can
demonstrate the principle of lift to the children by asking them to blow across a
strip of paper that is weighted down at one end. The paper lifts, rather than
flattens, as they probably expected it to, and thus the principle is demonstrated.
This work can lead on to many areas of investigation into windproofing. Below
we suggest some other activities that will help the children to investigate the
concept of windproofing.
The wind can sometimes be so strong that it takes your breath away. How
are prams and buggies designed to prevent this happening to babies and
toddlers? Can you set up an investigation to discover just how windproof
these vehicles are?
Devise an investigation to test the efficiency of various materials and
designs for draught-excluders. (One way of doing this is to make a draughtexcluder to go around a shoe-box lid. Put a wind source into the box, close
the box and measure the air movement around the lid.) Try designing and
making your own draught-excluding device for a classroom window or a
door.
How windy is the school environment? Litterbins and dustbins may be
vulnerable to sudden gusts. Alleyways where bins are often left out may be
particularly draughty. Investigate wind speeds around the school and use the
,
SCIENCE FOR PRIMARY TEACHERS
results to suggest better positions for litterbins and dustbins. Design and
make a windproof litterbin.
Finally, here are a couple of activities to show how we can have fun with wind.
Wind direction can be shown by looking at the direction taken by soap
bubbles as they float away. First, blow lots of soap bubbles in the air, in a
relatively open area, such as a school playing-field. Ask some children to go
downwind and stand in the path of the bubbles. The direction in which they
move will be the opposite of the direction from which the wind is blowing.
Now try the same thing near to a group of buildings. The eddies created as
the wind moves between the buildings can be clearly seen, and the variety of
directions taken by the bubbles makes it impossible to tell which way the
wind is blowing.
A local f6te will sometimes hold a balloon race, where helium-filled
balloons are released. A small card with the competitor's name on is attached
to each balloon; wfioever finds the balloon is asked to return the card, stating
where it was found. The winner is the person whose balloon has travelled
the furthest. Ask the organizers to let you have the returned cards, and plot
on a map all the places where the balloons were found. Find out the
direction of the wind on the day of the fete (from the daily weather map in a
newspaper). Did the balloons travel in the direction you would have
expected?
KEY POINTS
Wind is moving air. Its speed is measured using an anemometer; its
direction using a weather vane or wind sock. The Beaufort scale of wind
force assigns a numerical value to an observed effect of the wind.
Winds blow from areas of high pressure to areas of low pressure.
The direction from which the wind blows has considerable influence in
determining our weather.
IDEAS FOR RECORDING AND
USING DATA OBTAINED FROM A
WEATHER STATION
A weather station provides the ideal opportunity for the systematic recording of a
number of measurements connected with weather.
Children's first measurements and recordings of weather can be quite simple.
Very young children may simply look at the weather in comparative terms and
record whether it is windy, rainy, sunny, and so on. Many infant classrooms put
up boards containing simple descriptions of weather conditions. However,
children may feel more responsibility for their work if they design their own
information boards. They will thus progress in their recording skills from the
simple pictorial recording of weather conditions in key stage 1 to the more
sophisticated analysis of a number of variables in key stage 2 and beyond.
When recording the weather children should first be encouraged to devise their
own symbols for the various elements they observe and measure, such as rain,
snow, and so on. They can then be introduced to the standard symbols as found
on weather charts.
Key stage 2 work might involve the children, for example, using average
monthly temperatures to show differences between the seasons of the year. If a
record is kept of precise maximum and minimum daily temperatures the children
could investigate the correlation between the temperature and the first budding of
spring flowers, or blossom appearing on the trees.
THE WEATHER
Pressure and the amount of rainfall can be logged and plotted together in different
seasons. A study of pressure, amount of rainfall and temperature throughout the
summer will show that on those days when pressure is above 1000 mb little or
no rainfall occurs; this observation can then be linked to temperature to check for
patterns.
If a wind rose has been used to plot wind direction can they see any change in the
dominant or prevailing wind direction throughout the year? With encouragement
and careful record-keeping a library containing several years' worth of data for the
school can be collected; this could form a useful long-term project.
7 CONCLUSIONS
Work on temperature, rainfall, pressure, humidity and wind, together with visual
observations of visibility and cloud cover will give ample scope for lots of
interesting constructional and investigative projects. In general, although it is
fun to make your own measuring instruments, which show the principle of
operation, these are rarely robust enough to stand up well to continuous outdoor
use. So, for taking measurements over a long period, simple commercial
instruments are worth the extra expense.
Educational suppliers' catalogues will generally show many of these simple
weather instruments; some of them may be bought over the counter in highstreet shops or garden centres. There are a- few compa&es in the UK who make a
large number of suitable instruments. Details are given in the Resources Section.
Weather studies encourage children to become more observant and more aware of
the effect that the atmosphere has on all our lives. Today, virtually every
significant process and trend within the Earth's atmosphere is closely monitored.
Weather satellites orbiting the Earth record such things as the movement of air
masses, the distribution of water vapour and the fluctuation of temperatures at
different altitudes. Balloons carry sophisticated instruments high into the air to
collect data on winds and pollution. Yet despite the wealth of information from
these various sources, we are still not able to forecast the weather in detail for a
'
month ahead. We now know that this is because the Earth's atmosphere is a
chaotic system-small uncertainties in our knowledge of the atmosphere and
weather today will always imply that there will be large uncertainties in a longrange forecast. Given these new lessons and problems, perhaps we have now
reached the limit of weather forecasting. Despite all the scientific research, the
atmosphere's behaviour and structure still provide us with mysteries which will
provoke new ideas and theories for some time yet.
RESOURCES
USEFUL MATERIALS
Atkinson, B. W. and Gadd, E. (1986) Weather:A Modem Guide to Forecasting,
Mitchell and Beazley.
BP Cloud Charts I and 11, BP Educational Services, Wetherby, Yorkshire.
File, D. (1990) Weather Watch, Fourth Estate.
Jennings, T. (1990) Weather Watch: A Complete Weather Pack for Juniors,
Hodder and Stoughton.
Pedgley, D. E. (1980) Running a School Weather Station, Royal Meteorological
Society.
The Weather: Activity Sheets (1991) available from: Questions, 516 Hockley
Hill, Birmingham B 18 5AA.
The Weather: Resource Pack (1990) Supplements to Questions 2 (7), (8), (9).
Wilson, F. and Mansfield, F. (1979) Spotter's Guide to the Weather, Usborne.
SCIENCE FOR PRIMARY TEACHERS
EDUCATIONAL SUPPLIERS
E. J. Arnold & Son Ltd, Parkside Lane, Dewsbury Road, Leeds LS11 5TD.
James Galt & Co. Ltd, Brookfield Road, Cheadle, Cheshire SK8 2PN.
Philip Harris Ltd, Lynn Lane, Shenstone, Staffs WS14 OEE.
Hestair Hope Ltd, St Philip's Drive, Roydon, Oldham, Lancs OL2 6AG.
NES Ltd, 17 Ludlow Hill Road, West Bridgford, Notts NG2 6HE.
Osmiroid Educational, E. S. Perry Ltd, Os,miroid Works, Gosport, Hants.
INSTRUMENT MANUFACTURERS AND SUPPLIERS
Brannen Thermometers, Cleator Moor, Cumbria CA25 5QE.
Casella London Ltd, Vale Road, Bushey, Herts.
Diplex Ltd, PO Box 172, Watford, Herts WD1 1BX.
Met-Check, PO Box 284, Bletchley, MK17 OQD.
ACKNOWLEDGEMENTS
Grateful acknowledgement is made to Dr Geoff Jenkins and other members of the
Royal Meteorological Society for contributing much of the material used in the
preparation of this booklet. We would also like to thank Questions magazine for
allowing us to use extracts from their Weather Resource Pack supplements in the
Teaching notes.
ISBN 0 7492 5027 5
THE OPEN UNIVERSITY