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SCIENCE FOR PRIMARY TEACHERS Theopen 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