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Relevant Learning Objectives
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Understand the role of air masses and fronts in weather.
Understand the basics of population dynamics.
Understand and calculate density.
Understand the properties of waves and the electromagnetic spectrum.
Compare and contrast sexual and asexual reproduction.
Critique and improve the validity and reliability of data and experimental procedures.
Understand and apply Newton’s Laws of Motion.
Understand how electricity and magnetism relate.
Relate state of matter, contraction, and expansion to the motion of molecules.
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Understand the role of air masses and fronts in weather.
Students should understand air masses and fronts and how they impact weather. This
includes knowing the role of changes in air temperature and air pressure.
Tutorial:
If you were asked to describe the weather, certain words might come to mind, such as rainy,
hot, clear, windy, or partly cloudy. You would actually be describing the atmospheric
conditions of your location. Walk outside together and have the student report the weather for
you. Help him or her to include these conditions in the description: air temperature, wind,
cloud cover, precipitation, and humidity (amount of moisture in the air).
Weather is affected by various factors, including climate, season, location, and landmasses. As
the student learned in an earlier grade when studying climate, weather conditions can be
impacted by geographical features, such as oceans that moderate weather, as well as latitude.
This tutorial will cover the role of air masses and fronts in weather as well as how differences
in air temperature and pressure impact weather.
Air Masses
As you know, the weather is constantly changing. You can surely recall mornings that
promised a clear and pleasant day, only to be followed by thunderstorms in the afternoon.
This is because air is always in motion. As air moves from one place to another, it brings with
it different weather conditions.
When weather changes, it is due to movement of the atmosphere in the form of air masses.
An air massis a large body of air that has similar moisture and temperature conditions
throughout. You experience weather associated to the air mass you are in - for instance, you
feel the temperature and humidity of the air mass around you.
Air masses can form over bodies of water, such as oceans, or over landmasses, such as
continents. The temperature and humidity of an air mass are determined by the area over
which it formed. For example, an air mass that formed over tropical seas would be warmer
and wetter than an air mass that formed over a polar landmass.
These air masses move both horizontally and vertically. When they move horizontally, they
pass over new terrain. This causes them to change as they exchange such things as heat and
water with the terrain below. For example, an air mass that formed over a polar landmass will
warm up as it moves south and is heated up by the warmer landmasses it is passing over. Air
masses move vertically when they run into something, such as a mountain, or because they
become less dense. This occurs because of a change in temperature. The student has already
learned about the movement of molecules at different temperatures. As a review, point out
that at higher temperatures, molecules move more quickly and expand, that is, spread farther
apart. This is why warmer air is less dense and rises.
Air Temperature and Clouds
Warmer air can also hold more moisture, or humidity, than cooler air. Since the water
molecules in cool air are closer together, they collide more easily and join together to form
water droplets (condensation). Therefore, as warm, moist air cools, and is no longer able to
hold the same amount of moisture, some of the water vapor condenses onto tiny particles
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such as dust in the air and we get clouds! The student has learned the basics of cloud
formation in an earlier grade, but let’s explore it in more detail now.
Activity 1: Examining Cloud Formation
For this activity, you will need the following:
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A clear two-liter bottle with lid
Hot water
Matches
A piece of black construction paper (optional)
First, pour hot water into the clear bottle until it has about an inch or two of water in the
bottom and quickly put the cap on it. Shake the water around a little. Since the water is hot,
some of it will evaporate into the surrounding air and this water vapor will be trapped in the
bottle. This represents the atmosphere with high humidity or a lot of moisture in the air.
Now remove the lid and carefully place a lit match into the bottle, quickly replacing the lid.
(Please do not have the student do this part of the experiment.) The match should burn out
right away, but some of the smoke will be trapped in the bottle. This will provide the small
particles that are in the atmosphere needed for cloud formation.
Now that you have two ingredients for cloud formation (moisture in the air and small
particles), you will need a change in temperature. Make sure the lid is on tight and squeeze
the bottle hard, holding it for several seconds. When you release the bottle, the volume inside
the bottle will quickly increase, causing the temperature to slightly drop. What do you
observe? When you released the bottle, you should have observed the formation of a cloud
inside the bottle. The small decrease in temperature you created when you released the bottle
was enough to cause water droplets in the air to condense on the smoke particles, forming a
cloud!
Note: This experiment produces a very subtle cloud. If you do not see one after the first
squeeze, keep squeezing and releasing until you do see one. Sometimes holding the bottle up
to a piece of black construction paper can also make it more visible.
Squeeze the bottle again and hold it in this squeezed position. This will slightly increase the
temperature of the air inside the bottle. What happens now? The cloud disappears again since
by squeezing the bottle you increased the temperature of the air and it can now hold the
water vapor again.
Discuss with the student how this experiment compares to cloud formation in the atmosphere.
Ask what would happen if you tried this experiment without dropping the match in the bottle.
Give it a try, and ask him or her to explain why a cloud didn’t form. There were no particles in
the air in the bottle to help the small, condensed water drops collect, so no cloud can be
formed.
Air Pressure
Air temperature also impacts the air pressure. As air warms up and expands, the spread out
molecules run into each other less often, producing less pressure. A difference in pressure
leads to wind. Air moves from areas of high pressure to areas of low pressure. Since cooler,
denser air has higher atmospheric pressure and warmer, less dense air has lower atmospheric
pressure, this also means that wind moves from cooler areas to warmer areas.
Activity 2: Simulating wind
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For this activity, you will need the following:
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A balloon
Help the student visualize air movement from higher to lower pressure by blowing a balloon
full of air and holding the opening shut. Explain how the outside of the balloon is exerting a lot
of pressure on the air inside. When you release the opening, the air under pressure in the
balloon will blow like wind to the surrounding air, which is under less pressure. The larger the
difference in pressure in two areas, the stronger the wind will be!
Fronts
Since air masses are constantly moving around the earth, their paths often cross. When two
air masses of different conditions collide, significant weather changes occur. A front is where
two air masses meet. As the air masses interact, there are usually changes in temperature,
wind direction, pressure, moisture, and precipitation. The four types of fronts the student
should know are listed and described below. When discussing these fronts, a warm air mass
refers to the air mass that is warmer, wetter, and less dense relative to the other air mass;
the cold mass is the cooler, drier and denser of the two.
1. Cold Fronts
A cold front occurs when a cold air mass moves toward a warm air mass and overtakes
it. The colder, denser air will force itself under the warmer air, lifting it upward which
causes it to cool. And remember what happens when warm, moist air is cooled? Cloud
formation results. When the warm, moist air is suddenly lifted up, it cools quickly and
condenses, and relatively violent storms are likely to result as the front passes. After a
period of precipitation, cold fronts are often followed by colder, clear weather, as the
colder, drier air mass replaces the warm air mass that was originally present.
2. Warm Fronts
A warm front occurs when a warmer air mass approaches and overtakes a cold air mass,
sliding over the denser air. It lies over the cold air at a slight angle, often producing a
layer of clouds where the two fronts meet. Warm fronts are usually slower moving than
cold fronts, with the warmer air mass slowly displacing the colder air mass. This can
result in hours or days of precipitation. And when the warm air mass has successfully
replaced the cold air mass, the air takes on its characteristics— warmer and more humid
than the cold air mass.
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3. Occluded Fronts
An occluded front occurs when a cold air mass catches up with a warm air mass that is
bordered on the far side by cool or even colder air. The faster moving cold air mass
forces the warm air mass to be lifted up as it closes in on the cooler air. Predictably,
clouds and precipitation occur.
4. Stationary Fronts
A stationary front is when cold and warm air masses move toward one another and then
remain in the same place, with neither air mass overtaking the other. These are similar
to warm fronts, but can result in persistent precipitation for a week or more until the air
masses are finally able to move.
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Activity 3: Reviewing Fronts
Encourage the student to test his or her knowledge of air masses by providing weather
scenarios and asking him or her to determine the fronts and air masses involved. Below are
some suggestions:
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Gladville was experiencing a warm, muggy summer day when winds started to blow.
Suddenly, the sky was full of storm clouds, thunder and lightning. By evening, the storm
had passed and it was cool and clear outside.
What type of front probably passed through? Describe the types of air masses involved.
(Answer: cold front; cold air mass replaced warm air mass)
The people of Silverton were tired of rain. It had been more than a week, and the gray
skies were still sputtering rain. There seemed to be no end of rain in sight.
What type of front was probably present? Describe the types of air masses involved.
(Answer: stationary front; cold and warm air masses at a standstill)
It may be helpful for the student to sketch the types of fronts involved in the weather
scenarios you discuss to better understand what happens as air masses interact. Ask him or
her to explain the illustrations to you, including reference to cloud formation and changing
atmospheric conditions.
Review:
Explain how clouds form.
Describe how a cold front occurs.
Describe weather conditions that might follow a warm front.
Compare properties of warm and cold air masses.
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Understand the basics of population dynamics.
Students should understand the basics of population dynamics. They should also be able to
predict the impact of changes in abiotic factors (i.e. soil properties, amount of light, etc.) and
biotic factors (other organisms) of an environment on populations.
Tutorial:
Defining Population
Ask the student what we are discussing when we talk about the population of the United
States. The student should realize that we are talking about all of the people who live here.
When we use the term population in life science, it means something more general. It means
the number of individuals of a particular species that live in an area. For example, scientists
might discuss the population of lions in the Maasai Mara, Africa, or the population of live oaks
in Savannah, Georgia.
Activity 1: What Affects Population Size?
For this activity, you will need the following:
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Paper
A pen or pencil
Ask the student to list as many factors as he or she can that can affect the size of a
population. A great place to start is by thinking about organisms’ basic needs (i.e. food, water,
shelter, etc.) and the various ways that plants and animals meet these needs. The student
should also consider environmental factors that may pose difficulty for organisms to meet
their basic needs (i.e. pollution, competition, etc.). If basic needs are not met, organisms will
die. If these are easily met, organisms will thrive. The student’s list may include such items as
the following: amount of water, amount of food sources, amount of sunlight, quality of the
soil, number of predators, degree of competition for resources, availability of shelter, air
quality, water quality, and prevalence of diseases. When the student is done, review his or her
list together, clarifying any entries as well as adding as many factors as you can.
Now have the student look at his or her list and classify the factors listed into two categories:
those that have to do with biotic or living factors in the environment and those that have to do
with abiotic or nonliving factors. Have the student put a "B" next to all of the biotic factors and
an "A" next to all of the abiotic factors on his or her list. For example, "number of predators"
has to do with other living things in the environment and should have a "B" next to it.
"Amount of sunlight" has to do with nonliving factors in the environment and should have an
"A" next to it. Review the student’s classifications, correcting any errors.
Now discuss how changes in each of these factors can cause a population to increase or
decrease. For example, water is a basic need of most organisms. If the amount of water
available to a particular population increases, perhaps the size of the population will increase
since there is more of this vital resource available to each organism. However, if the amount
of water available to this population decreases, the size of the population may decrease since
there is less of this vital resource available. Be sure to discuss each factor in this way.
Is Population Growth Always Good?
Often we assume that population growth is a good thing. The organisms seem to be thriving;
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therefore, the environment they are living in must be healthy. This is not always true. Maybe
most of the natural predators of a species have been killed by hunters, and now the species’
population is growing out of control. This will be happening because the natural balance is off,
and the environment only seems healthy. The white-tailed deer is an example of this. Its
natural predators, wolves and mountain lions, have decreased in large part to over-hunting in
some areas, and now there is overpopulation of deer in these areas.
A particular population can also get too big for the supporting environment. When this
happens, the population will plateau because the resources (i.e. food, water, etc.) in the
environment cannot support more organisms. When this happens, the population has reached
its carrying capacity. Look at the graph below which shows how a population will grow until
it reaches this point.
Activity 2: Modeling Population Changes
For this activity, you will need the following:
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Graph paper
A pencil
40 dried black beans and 40 dried lima beans (or any two types of dried beans or coins
that are different colors)
Give the student a piece of graph paper. Tell the student that he or she is going to track a cat
population. Have the student label the x-axis "Years." Have the student label the lines in this
axis from 0 to 10. Have him or her label the y-axis "Cat Population Size." Have him or her
label the lines on this axis from 0 to 70, skipping by fives. His or her initial graph should look
like the one below:
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Now give the student a dried black bean and a dried lima bean. Tell him or her that the black
bean represents a male cat and the lima bean a female one. These two cats are going to be
the beginning of a cat population in your neighborhood park. Have the student mark at year
zero the population size of the cats, 2! Now tell the student that the two cats have 3 babies
the first year - two girls and one boy. Have the student get two lima beans and one black
bean to represent these babies. What is the size of the cat population now? 5! Have him or
her record that the population size was 5 at year 1 on his or her graph. Now tell the student
that each year, each male and female couple will have 3 babies, 2 girls and one boy. Have
him or her track the population size for the next 3 years using beans and the graph.
Now during the fifth year, a disease comes through the park, and almost half of the cat
population dies - 15 of the females and 8 of the males. Also, no babies are born this year.
Have the student remove these beans and record the new population on the graph. During the
next 5 years, each remaining couple has only two babies, one male and one female until they
reach the environment’s carrying capacity, 60. The population plateaus at this level and, at
this point, assume that for each baby born, an older cat dies due to lack of resources. Have
the student finish using his or her beans to track this population and record the findings on his
or her graph. His or her final graph should resemble the one below:
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Review:
What is a population?
What are some factors that cause a population to increase? To decrease?
What does carrying capacity mean?
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Understand and calculate density.
Students should understand and calculate density. They should also understand how mass,
volume, and density relate and be able to predict interactions of materials of various
densities.
Tutorial:
For this tutorial, you will need the following:
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2 boxes: one that is medium to large, and another that is about half of its size
Objects, such as toys and books, to put into the boxes
2 clear glasses
Some water
Cooking oil
Liquid dishwashing soap, preferably not yellow in color
Dark corn syrup
Food coloring (optional)
A plastic spoon
A foam packing peanut
A small metal paper clip
A small piece of a candle
Cupcake sprinkles
Introducing density:
Explain to the student that he or she is going to think about how the volume and mass of
things are related. Point out that volume is a measurement of the amount of space that
something takes up. Mass is the measurement of the amount of matter or material of which
something is made.
Ask the student, "If you had the same volume of two different substances, would their masses
be the same?" Imagine a bowling ball and a rubber ball that are the same size, and thus have
the same volume. Would their masses be the same? They would not be; the bowling ball
would have a larger mass.
Next ask, "If you had the same mass of two substances, would their volume be the same?"
Imagine 5 kilograms of iron and 5 kilograms of air. Would they take up the same amount of
space? The 5 kilograms of air would have a much larger volume. So, the volume and mass of
different substances are very independent of one another. This is why there is density. How
these two values relate in an object or substance is its density. Density is a ratio of mass and
volume, and really measures how tightly packed the material that makes up something is.
Mathematically, density is equal to mass divided by volume. For example, if an object has a
mass of 25 kilograms and a volume of 5 cubic meters, its density is 25 kilograms/ 5 cubic
meters = 5 kilograms per cubic meter. Though the formula may be easy enough to memorize,
the concept can be tricky. Let’s think about density intuitively.
Activity 1: What happens to density if you change the amount of mass put in the
same volume?
Obtain a medium sized box and put various books, toys or other objects into it until it is about
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half full. Close the box and have the student lift it. Now add more books, toys, or other
objects to the box until it is very full. Close the box and have him or her lift the box again. Ask
if it is heavier than it was before. The student should note that it is heavier and therefore has
more mass.
NOTE: Be sure to use a box that is big enough and materials with enough weight so that
there is a significant difference in the weight of the box when it is half full and when it is
full.
Now ask, "Did the mass of the box change?" The student should realize that by adding more
matter (i.e. toys, books, etc.) to the box, the mass of the box did increase, which was also
indicated by the increase in weight. Next ask if the volume of the box changed. He or she
should realize that the amount of space that the box takes up remained the same. Finally ask,
"Is the box more or less dense?" The student may struggle with this one, so guide the student
to the realization that the box is now denser. Therefore, when you add more mass to the
same volume, it becomes more dense. Discuss how this example would look using the
equation. If you have the same volume - say 100 cubic centimeters, but increased the mass
from 500g to 1000g, what happens to the density?
Density before = mass/volume = 500grams /100 cubic centimeters = 5 grams per cubic
centimeter
Density after = mass/volume = 1000 grams/100 cubic centimeters = 10 grams per
cubic centimeter
Of course the opposite is true as well. When you remove mass from the same volume, it
becomes less dense. Have the student remove all of the objects from the box and try lifting it.
Ask the same line of questions as you did before. He or she should realize that the mass was
decreased as objects were removed, that the volume of the box was still the same, and that
the empty box is less dense. Use the equation to explore this scenario as well. Let’s imagine
that you have the same volume of 100 cubic centimeters again, but this time you decrease
the mass from 500 grams to 100 grams. What happens to the density?
Density before = mass/volume = 500 grams/100 cubic centimeters= 5 grams per cubic
centimeter
Density after = mass/volume = 100 grams/100 cubic centimeters = 1 gram per cubic
centimeter
Activity 2: What happens to density if you change the amount of volume that a
constant amount of mass is contained in?
Refill your box until it is half full. Now find a smaller box, one about half the size of the one
you have been using. Put all of the objects that were in the larger box into the smaller box.
Ask the student if the volume of the two boxes is different. He or she should recognize that
the smaller box has less volume. Now ask, "Did the mass of the objects change when we
moved them from one box to the other?" The student should understand that the mass
remained the same since nothing was added and they would still read the same on a balance.
Now ask which box is denser when it is full of the objects. Guide the student to the
understanding that the smaller box is denser. Once again, use the equation to demonstrate
this. Imagine that the larger box still has a volume of 100 cubic centimeters, and the smaller
box is about half this size, so we will say that it has a volume of 50 cubic centimeters. Let’s
say that the objects that we moved between the boxes have a mass of 500 grams.
Density of larger box = mass/volume = 500 grams/ 100 cubic centimeters = 5 grams
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per cubic centimeter
Density of smaller box = mass/volume = 500g/ 50 cubic centimeters = 10 grams per
cubic centimeter
Therefore, we learn that when you put the same mass into a smaller volume, it becomes more
dense. The reverse of this is also true. If you move the objects from the smaller box, back to
the bigger box, the density is decreased from 10 to 5. Thus, it is also true that when you put
the same mass into a larger volume, it becomes less dense.
NOTE: A common misconception of students is to think that just because something has more
mass, it is denser. They also often believe that whichever item has the greatest volume is the
least dense. Remind the student that this is not the case. How the mass or volume of two
objects individually relate has nothing to do with how their densities relate. Only if their mass
or volume is the same can such comparisons be made. You must always use the mass and
volume of both objects to be sure of your answer. Have him or her think of a very large pile of
leaves that is heavier, and thus has more mass, than a 40-pound barbell. Which would be
denser? Even though the pile of leaves has more mass, the mass is spread out over a large
volume. Therefore, the leaves are less dense.
Activity 3: How objects and substances with different densities interact
Point out that objects and substances of different densities interact in predictable ways. Do
the following experiment with the student to illustrate this:
Put a quarter cup of cooking oil in a clear glass. Predict what will happen when you pour a
quarter cup of liquid dishwashing soap into the oil. Will the liquids mix or will they separate? If
they separate, how will they look? Test your prediction by adding the soap to the oil and
observe the result.
In a second clear cup, pour a quarter cup of water. You can add some food coloring to the
water if you want to make it more visible. Just be sure to use a different color than those of
the other liquids. What do you think will happen when you pour a quarter cup of dark corn
syrup into the water? Once you have made a guess, add the corn syrup and observe what
happens.
Now try to predict what will happen if the contents of the second cup are poured into the first
cup. Will the liquids settle into layers or mix now? If they do settle into layers, in what order
will they do so? When you are ready, pour the contents of the second glass into the first one.
Be sure to let the liquids settle and do not stir them. Were you right?
Ask the student why he or she thinks that the liquids formed layers. It is because they have
different densities (This actually also involves the surface tension of liquids, but since this is
not the subject of this activity, we will focus on the density aspect of the phenomenon.) A
more dense liquid will settle below one that is less dense. Therefore, the liquids settle into
layers according to their densities - from the densest liquid, which settles at the bottom of the
glass, to the least dense liquid, which settles on top.
Ask the student, "What do you think will happen if we add solids to these liquids?" Gently drop
a small piece of the handle of a plastic spoon into the glass. Where will it settle? Also try a few
cupcake sprinkles, a small metal paper clip, a small piece of a candle, and a small piece of a
foam-packing peanut.
What happened? When we add solids, the solids are also sorted into layers by their densities.
An object will float on a liquid that is denser than it, but will sink through a liquid that it is
denser than. This means that a small object can end up floating between two liquid layers,
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below the one that is less dense and above the one that is denser. If a small object has the
same density as a liquid layer, the object will float in the middle of that layer.
Let the student test the relative density of other small objects. When he or she is done
experimenting, ask him or her to list the liquids and objects in order of their densities - from
the densest to the least dense. If 2 items have the same density, they can be written
together. (If two objects are floating on top of all of the liquids or sink through all of the
liquids, their relative densities cannot be determined so the student can just note this on his
or her list.)
Review:
What is density?
How do you calculate density?
You have two boxes that both have a volume of 100 cubic centimeters. Box A has a mass of
50 grams and Box B has a mass of 100 grams. Which box is denser?
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Understand the properties of waves and the electromagnetic spectrum.
Students should know that energy travels in waves and the properties of transverse waves
(frequency, amplitude, wavelength). This includes understanding how the properties of waves
relate to each other and to the energy of the wave. Students should also know the
electromagnetic spectrum and the basic properties of its parts.
Tutorial:
Tutorial: What is a wave? What is the electromagnetic spectrum?
For this tutorial, you will need the following:
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A Slinky , jump rope, or other length of rope
A ribbon
Access to the Internet or encyclopedias
Introduction to Waves:
Waves are everywhere around us. Ask if the student can think of any examples of waves. We
can watch them in the ocean, they help sound to reach our ears, they are involved in the light
rays that help us see, they can be felt when we experience an earthquake, we can see how
they cook things in a microwave, and we can even make one in a stadium when we are
watching a sporting event.
But what is a wave? A wave is a way that energy is transported from one place to another
without actually moving any matter. Matter is only ‘disturbed’ or displaced temporarily from
its natural rest position as the energy moves through it. This disturbance, and the energy, is
passed from one particle to another as the wave moves through a medium (any substance air, water, a Slinky , a rope, etc.). Imagine that one particle receives energy and is
displaced. It then passes on this energy and displaces the particle next to it. The first particle,
having passed on the energy, returns to its original position and energy level. The second
particle then passes on the energy to the particle next to it and it returns to its original state.
Now the third particle is displaced, and so on and so on... A wave in a stadium at a baseball
game demonstrates this well. Imagine that all the fans are in their resting positions calmly
sitting in their seats. The first fan in a wave gets some energy and is disturbed or displaced,
standing up. As the fan sits down, returning to his or her original state, the energy is passed
to the fan next to him or her. This fan is then displaced standing up. As this fan sits down, the
energy is passed on to the next fan. This process continues, passing the disturbance and the
energy around the stadium. However, no one person actually changed seats, just like no
particles of the medium change positions when waves pass through it.
Transverse Waves:
There are various kinds of waves and they are sorted using various properties. One way that
waves are categorized is by the relative direction of the particles of matter to the direction
that the wave is moving. The student is going to learn about one of these types of waves,
transverse ones, in more detail. The particles of the medium in a transverse wave are
displaced in a direction perpendicular to the direction that the wave is traveling. Think back to
the stadium wave example. The energy and the disturbance of the wave move from left to
right around the stadium. But the individual fans, like the individual particles, are displaced
perpendicular to this. They move up and down!
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Use a Slinky to create a wave. (If you do not have one, you can use a jump rope or other
length of rope). Every wave begins with a particle being displaced. In this case, your hand will
displace the first coil of the Slinky . To create a transverse wave, you need to displace the
first coil in a direction perpendicular to the length of the Slinky - or up and down. To do this,
lay the Slinky on the floor. Tie a ribbon to a coil near the middle of the Slinky . Grab the
first coil of one end of the Slinky . Move it back and forth across the floor in this direction
and watch what happens. A wave travels from one end to the other end! Observe the ribbon.
Notice how it just bounces up and down, like the fans in the stadium, as the wave travels
past. (NOTE: The wave is much clearer if someone holds the opposite end of the Slinky
still).
Below is an illustration of a transverse wave. Each disturbance is represented by a hump,
which would travel down the Slinky . Numerous humps in a row make a continuous wave.
The blue line represents the position the Slinky would be in if there were no disturbance or
wave moving through it. We will call this its rest position. As you can see, when a wave is
passing through the Slinky , its particles move both above and below this rest position. The
highest point a particle in a wave is displaced above its resting position is called the crest.
The lowest point a particle is displaced below its resting position is called the trough. There
are three main properties of a transverse wave:
1. Amplitude: This is how big the wave is. It is the maximum amount that a particle is
displaced from its resting position. This can be measured from the resting position to the
crest or to the trough. Both values will be the same. The larger the amplitude, the more
energy the wave has. After all, it takes more energy to make a big wave!
2. Wavelength: If you look at the wave, you can see that it has a pattern like a repeating
S on its side. The wavelength is simply the length of one cycle of this repeating pattern.
It is defined as the distance from any spot on one cycle to the same spot on the next
cycle. Usually we use the distance between two crests when determining the wavelength
of a wave since this is clearest. The shorter the wavelength, the higher energy the wave
has. It takes more energy to get more cycles of a wave to pass by in the same amount
of time.
3. Frequency: This is the amount of wave cycles that occur in a second. If you could
watch one point or particle of a wave and count how many cycles of the wave’s
repeating pattern it went through in one second, you would have the frequency of the
wave! There is a relationship between the wavelength and the frequency of a wave. The
shorter the wavelength, the higher the frequency. Think about it. You can get more
cycles to pass by in the same amount of time if the cycle is shorter. So, following the
same logic, higher frequency waves have more energy.
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It is important to remember that the wave in this illustration is moving! In fact, its speed can
be determined by a very important formula that you should know. The speed of a wave is
equal to its wavelength multiplied by its frequency. However, as the wave moves, the
properties above will remain the same. This illustration is a snapshot a few moments after the
one above.
Ask the student what is the same and what is different about the wave now. He or she should
notice that the entire wave has shifted to the right. The crests and troughs are in different
locations now. Next, ask if the wavelength or the amplitude of the wave has changed. The
student should realize that these properties are still the same! Finally, point out the red dot on
the two illustrations. Explain that this represents one particle of the medium which the wave is
passing through. Point out that this particle does not move along with the wave. It just moves
up and down, like the ribbon on the Slinky , as the wave travels past.
The Electromagnetic Spectrum:
Another way to categorize waves is by whether or not they can transmit energy through
empty space. There are two main categories of waves when they are sorted this way:
mechanical and electromagnetic. Mechanical waves require a medium to send their
energy, like a Slinky , water, or air. On the other hand, electromagnetic waves do not
require a medium. Though they do travel through mediums, they can also travel through
space or a vacuum. (The details of how electromagnetic waves work are not taught at this
level.) The energy from the sun reaches the earth in this manner by traveling through space.
The various types of electromagnetic waves are portrayed in the electromagnetic
spectrum, EM spectrum for short. There are 8 main types of these waves: radio waves,
microwaves, infrared waves, visible light, ultraviolet light, x rays, gamma rays, and cosmic
waves. Notice that they are transverse waves and are classified and arranged by their
wavelengths - from the longest to the shortest as shown below. This spectrum is also
arranged and classified by the waves’ energy or their frequencies, since all the waves travel at
the same speed.
Have the student use the Internet or encyclopedias to research the eight types of
electromagnetic waves. He or she should discover how each type of wave is present in our
daily lives. For example, "What is a wave used for? Where does he or she encounter it? Where
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do they come from? Are any of the waves dangerous to humans? Which can we see?" Below
are some websites the student can use as resources:
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NASA;s IMAGERS at http://imagers.gsfc.nasa.gov/ems/waves3.html
Berkeley Lab’s Microworlds at www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html
Amazing Space at http://amazing-space.stsci.edu/resources/explorations/light/emsframes.html
Review:
What is a wave?
What are the crest, trough, wavelength, amplitude, and frequency of a wave?
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Compare and contrast sexual and asexual reproduction.
Students should be able to differentiate between the basic advantages, disadvantages, and
processes of sexual and asexual reproduction.
Tutorial:
Explain to the student that all living things reproduce or produce offspring. Since no organism
lives forever, reproduction is necessary for the continuation of a species. There are two ways
that living things reproduce: sexually and asexually.
Briefly introduce sexual reproduction to the student. This is how most animals and plants
reproduce. Humans have babies and dogs have puppies in this way. Sexual reproduction is
when offspring develop from the union of the genetic material from two parents, a male and a
female. Each parent contributes a distinct type of gamete, or sex cell, which contains half of
the parent’s genetic material. The female’s sex cell is an egg or ovum, and the male’s is a
sperm. When an egg and a sperm unite, fertilization has occurred and an offspring begins to
develop. Since the offspring in this process receives half of its genes from the male and the
other half from the female; it is not identical to either parent.
Next, briefly explain asexual reproduction. This type of reproduction involves only one
parent. Each offspring has the exact same genes as the parent and is therefore identical to, or
a clone of, the parent. The most common process for asexual reproduction is binary fission.
The organism duplicates its DNA and then splits, producing copies of itself. Bacteria reproduce
this way.
Ask the student, "What do you think are the advantages and disadvantages of each type of
reproduction?" Guide him or her to the main results of each type of reproduction listed below.
Sexual Reproduction:
 Creates genetic variation since each offspring has half of the genetic material of two
different parents. This allows adaptation to changing environments. However, it also leads to
the loss of advantageous traits that a parent may have.
 Takes a lot of energy. Special sex cells must be produced and the male and female sex cells
must find a way to be united. Thus, it is more difficult to produce large populations.
Asexual Reproduction:
 Creates clones with no variation since all of the genetic material in each offspring is an
exact copy of one parent’s genes. This does not allow adaptation to changing environments.
Therefore, if the environment changes, all of the individuals could perish. However, if the
environment is stable, it also leads to maintaining advantageous traits.
 Takes very little energy. No special sex cells need be created and every asexual organism
can reproduce on its own. Thus it is easy to produce large populations.
Finally, have the student research the following questions about sexual and asexual
reproduction using the Internet or encyclopedias:
Do flowering plants reproduce sexually or asexually? What is unique about the way
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that they reproduce?
These plants reproduce sexually; however, each plant produces both the male and the female
sex cells. Then the male sex cell from one plant fertilizes the female sex cell of another plant.
There are other ways besides binary fission that organisms reproduce asexually.
Briefly explain some of these processes and list an organism that uses each one.
Some common examples are budding, grafting, fragmentation, and parthenogenesis.
Do any organisms reproduce both sexually and asexually?
Yes. Bees and jellyfish are some familiar examples.
Do humans use asexual reproduction in any way?
Not technically. Human cells do divide to create identical copies of themselves through a
process called mitosis. mitosis is similar to the asexual reproductive process, binary fission.
We use the new cells created for growth, development, and maintenance. However, since
each of our cells is not an organism, it is not technically reproduction.
After the student has completed researching these questions, review and discuss what he or
she has discovered.
Things to keep in mind:


It is not important that the student know the specific terms presented here (i.e. gamete,
the various asexual reproductive processes, etc.). It is necessary only that he or she
understands the main concepts.
There are exceptions to many of the generalizations in this tutorial. For example,
tapeworms self-fertilize and, thus, sexually reproduce without two parents. However, for
the purposes of this level, addressing these is not necessary and could cause confusion.
If the student discovers some exceptions during his or her research, explain that the
rules discussed here are true for most living things.
Review:
What are the major differences between sexual and asexual reproduction?
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Critique and improve the validity and reliability of data and experimental
procedures.
Students should be able to critique and improve the validity and reliability of data and
experimental procedures. This includes such skills as recognizing sources of error and unusual
data and understanding the importance of trials and sampling.
Tutorial:
When critiquing and performing scientific investigations, the student should keep in mind
reliability and validity. These will affect how confident you and others are about the
conclusions drawn from the results of an investigation.
Reliability:
Reliability refers to the repeatability of an experiment. Does the experiment consistently yield
the same results when it is conducted multiple times by various individuals? If so, the results
can be confirmed and the experiment is reliable. This doesn’t mean only the experiment as a
whole, but also any measurements taken as part of it.
As a simple example, imagine that the student takes a test that claims to determine at what
grade level he or she is reading. Its results say that the student is reading at a twelfth grade
level. The next day, he or she takes the test again and this time it tells that the student is
reading at the kindergarten level. Finally, on the third day, the test claims that he or she is
reading on the sixth grade level. Would you have any faith in the results of this test? No! The
same thing applies to data from an experiment. The results and measurements should be
consistent - or no one will have confidence in them.
Reliability not only allows scientists to verify results but also to eliminate and discover sources
of error. For example, a group of scientists are testing how salt affects the boiling point of
water. Each scientist is doing one trial of the experiment. They are measuring the boiling point
of 3 cups of water and then 3 cups of water with 2 teaspoons of salt dissolved into it.
Everyone’s results are within a degree of one another except for Sally’s. Sally’s saltwater
result is 15 degrees higher than anyone else’s. Most likely something went wrong with Sally’s
trial - maybe her thermometer is broken or she read it incorrectly. The group evaluates what
happened and discovers the source of error. Sally accidentally used 2 tablespoons of salt
instead of 2 teaspoons. Sally redoes the experiment being careful to use the right amount of
salt. She now gets a result that is similar to the rest of the team. If Sally had been the only
scientist conducting the experiment, the error would have gone unnoticed, and the results
would have been incorrect. Such scenarios demonstrate why performing many trials as part of
an experiment is important.
It is also important that others -- anywhere, anytime -- can read the procedure of an
experiment and repeat it. For example, another group of scientists read the results of the
experiment above done by Sally’s team. They decide to try the experiment themselves. This
team gets similar data. When an experiment is successfully repeated, like in this case, the
results can be accepted by others with confidence. This is why a procedure must be explained
clearly and in detail - so others can repeat it!
Validity:
Validity is the degree to which an experiment actually measures what it is intended to. There
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are two types of validity: internal and external.
Internal validity has to do with the validity within the experiment itself. The main focus of this
is whether you can justify that the outcomes that you measured and observed in your
experiment were caused by what you claimed they were. You have to set up your experiment
very carefully - for example, being careful to rule out any other causes for the outcomes you
observed as well as choosing your variables to be accurate representations of what you want
to measure. Imagine that you were trying to determine that caffeine makes people’s hearts
beat faster. Let’s say that you measured people’s heartbeats each morning and afternoon and
asked people how much caffeine they consumed during the day. You found that those people
who consumed more caffeine had a greater change in their heartbeat over the course of the
day. How do you know that the differences you observed in the amount that people’s
heartbeats changed were not caused by something other than the caffeine they consumed?
For example, maybe the results were caused by differing amounts of exercise or a difference
in how long ago the caffeine was consumed. You would have to set up your experiment in a
way that allowed you to eliminate these and other explanations for the results you found.
Also, asking people how much caffeine they consumed may not be a true representation of
how much they actually did consume. If you measured and controlled the amount of caffeine
each person consumed, the experiment would be more valid.
External Validity refers to the degree to which your findings can be generalized - or applied to
other people and circumstances. This means that you have to try to make sure that the
circumstances and people you use are representative. This is most important when you use
people as part of your experiment. For example, if you only used 100 friends your age for the
caffeine experiment mentioned above, it would not be considered valid for the general
population. Would people other ages respond the same way as people your age did?
The relationship between reliability and validity:
It is important to remember that these two concepts are independent of one another. For
example, you can have reliable results that are not valid or vice versa. Imagine that the
reading test mentioned above was reliable and consistently gave the student the same result
every day that he or she took it. It determined that the student was reading at the
kindergarten level. However, he or she was actually reading at the sixth grade level.
Therefore, this test is not measuring what it set out to measure and it is not valid. Just
because results are consistent, doesn’t mean they aren’t wrong or biased in some other way.
It is important that an experiment and its results be both reliable and valid.
Critiquing Experiments:
Have the student read the procedure of various experiments and judge their validity and
reliability. Have him or her justify his or her opinion. If appropriate, have the student suggest
what could be done to improve the validity and/or reliability of the experiment.
You can have the student use experiments that he or she is doing at school for this activity, or
you can search the Internet or check out books from the school or local library that suggest
science experiments.
Review:
What does it mean if an experiment is reliable?
What does it mean if an experiment is valid?
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Understand and apply Newton’s Laws of Motion.
Students should understand and apply Newton’s Laws of Motion.
Tutorial:
Point out to the student that he or she witnesses many forces and their impact on the motion
of objects every day. Some examples include the following: a car braking, a bicycle being
ridden, a door opening, and a book falling to the floor. However, we take these things for
granted and never stop to think that all of these common everyday events work on scientific
principles. A famous scientist named Isaac Newton identified three laws to explain the links
between force and motion. These are called Newton’s Laws of Motion.
Newton’s first law: An object at rest will remain at rest, and an object moving will
keep moving at the same speed, in the same direction, until an unbalanced or net
force acts on it.
The student was exposed to this law when studying balanced and unbalanced forces. Point out
that balanced forces are of equal magnitude or amount but act in opposite directions. Thus,
such forces balance or cancel each other out, so that it is as if no force were acting on the
object at all. In such cases, the object that the forces are acting on will continue doing
whatever it was doing - being at rest or moving with the same speed in the same direction.
Unbalanced forces, on the other hand, do not balance each other out. Either there is only one
force so there is not another force working against it, or one force is more powerful than the
other. Thus, there is a net force - which is the sum of their impact. For example, if you are
pushing on a block to the left using a force of 20 newtons, and your friend is pushing on the
same block using a force of 10 newtons to the right, what is the net force? 10 newtons to the
left! Net forces affect the motion of objects. They can start objects moving or stop them. They
can speed objects up or slow them down. They can change the direction in which objects are
moving.
However, a key part of this law that was not addressed in earlier grades is inertia. Inertia is
the property that an object has of resisting any change in its state (i.e. being at rest or its
current movement). Use the following common example to explain this to the student:
Ask if the student remembers ever riding in a car when the driver suddenly slammed on
the brakes. Ask how his or her body moved as the car came to a stop. He or she should
have felt his or her body move forward and hit the seatbelt with a jerk! Ask why his or
her body moved forward when the car stopped. After the student has made some
guesses, explain that it was inertia that made this happen. The student and the car were
moving along at the same speed and in the same direction. When the motion of the car
was stopped by the force of the brakes, he or she kept moving since the force of the
brakes did not act on him or her! So, since no force acted on the student, he or she kept
moving at the same speed, in the same direction as they were moving before. Now ask
what force did stop the student. (The seat belt) Without that, he or she would have kept
on going until something else acted that would stop his or her motion, such as the
windshield, a tree, or the road. This is why seatbelts are important.
Explain that objects with more mass have more inertia - meaning they are harder to start
moving or stop moving. Have the student think about the following: Which would be easier to
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begin moving if it were at rest - a car or a marble? The marble has less mass, so it has less
inertia. The same applies to stopping two objects moving at the same speed. The marble
would be easier to stop as well.
Newton’s second law: The net force (F) acting on an object is equal to the object’s
mass (m) times its acceleration (a); F = m x a
Have the student think about this conceptually. Place a bowling ball and volleyball in front of
him or her(You can use any similar sized balls with clearly different masses). Ask, "If you
applied a force of 10 newtons to both of these objects, which would accelerate more?" He or
she should realize that the volleyball would because it has less mass! Plug some imaginary
numbers into the equation to prove this. Tell the student to imagine that the bowling ball has
a mass of 10 kilograms, and the volleyball has a mass of 1 kilogram, just for simplicity. How
much would each of these objects accelerate?
Now tell the student to imagine that you placed a garbage can at one end of a driveway.
Imagine that he or she rolled the bowling ball, and then the volleyball, at the garbage can,
being sure that they both had the same acceleration when they reached the can. Ask, "Which
would hit the can with more force?" He or she should realize that the bowling ball would since
it has more mass. Let’s use an acceleration of 10 meters per-second squared to demonstrate
this example:
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Now have the student play with other scenarios, trying to answer them conceptually and then
plugging in imaginary numbers to see if he or she was right about the outcome. For example,
what if the student rolled two bowling balls at the garbage can, but they had different
accelerations? Which would hit the can with more force? Or, if he or she had two volleyballs
and pushed them with different amounts of force, which would accelerate more?
Newton’s third law: For every action, there is an equal and opposite reaction.
When two objects interact, they exert forces against each other. One exerts an action force,
and the other exerts a reaction force that is equal in size but opposite in direction. The two
forces are called an action-reaction force pair. The challenge is identifying these forces and
their directions. Share the following example with the student:
A soccer player kicks a soccer ball with a force to the left- this is the action force. The
ball exerts an equal force on the player’s foot to the right- the opposite direction.
The trick is to identify the two objects and then determine which one is doing the "acting."
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Next, determine the direction of this action force. The other object will be acting on the
"action" object with the same amount of force in the opposite direction. Have the student try
to identify the action-reaction force pairs in the following examples:
1. A person picking up a book
The person exerts an upward action force on the book, and the book exerts an
equal, downward force on the person.
2. A person rowing a boat
The oar being used by the person rowing exerts an action force on the water,
which in turn, exerts a reaction force on the oar.
Activity: Seeing Newton’s Laws in Action
For this activity, you will need the following:
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An empty film canister
An Alka Seltzer tablet
Some water
Safety goggles
A launching pad - a flat, open space to launch your film canister safely
Follow the steps listed below to launch a film canister into the air. As the canister flies into the
air, have the student think about how each of Newton’s three Laws of Motion are at work.
1.
2.
3.
4.
5.
6.
7.
Put on protective eyewear, such as goggles.
Fill an empty film canister about one-third full of water.
Cut an Alka Seltzer tablet in half.
Drop one half of the Alka Seltzer tablet into the film canister.
QUICKLY place the lid on the film canister.
Place the canister upside down on the open space you found.
Stand back and observe!
Newton’s first law is demonstrated when a net force causes the film canister to change its
motions and shoot up into the air. The unbalanced force is produced by the gas created in the
canister because of the reaction of the Alka Seltzer tablet and the water. This force
eventually blows the lid off of the film canister, forcing it upward.
Newton’s second law is shown by the film canister’s acceleration. It is the force with which the
gas blew the canister’s lid off, divided by the mass of the canister.
Newton’s third law is demonstrated by the canister and the ground that served as its
launching pad. The canister exerts a downward action force on the ground as its lid blows off;
the ground exerts an equal, upward reaction force on it.
Have the student look for other examples of Newton’s laws in his or her daily life. For
example, he or she may notice them at sporting events or even as the student struggles to
get ketchup out of a bottle!
Review:
Name Newton’s three Laws of Motion, and give an example of each.
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Understand how electricity and magnetism relate.
Students should understand that electricity produces magnetic effects and that moving
magnets produce electricity. This includes a basic understanding of electromagnets and their
uses.
Tutorial:
For this tutorial, you will need the following:
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A D-cell battery
A one-to two-foot piece of insulated wire
A compass
A nail
Metal paperclips
Other small objects to try as cores of the electromagnet, such as a screw, a wooden
pencil, a plastic pen, etc.
Access to the Internet or encyclopedias
Explain to the student that there is a special relationship between electricity and magnetism.
A current of electricity produces a magnetic field and moving magnets produce electricity. This
relationship is the basis of many devices that you use every day.
A current of electricity produces a magnetic field:
To help the student grasp this concept, begin with the following experiment that will
demonstrate that an electric current running through a wire does indeed create a magnetic
field:
Remind the student that a compass needle is actually a small magnet that reacts to the
magnetic field of the earth. This is how the compass finds direction. Begin by briefly
reviewing this concept. Then place a small compass on a table and observe that the
compass is indeed pointing north as it normally would.
Give the student the battery and the insulated wire. Be sure that an inch or so at each
end of the wire is stripped - that is, has the insulation removed. Ask him or her to make
a simple circuit using these materials while being sure that the center of the wire is near
the compass. To do this, have the student hold one stripped end of the wire to the
positive end of the battery (the one labeled with a plus sign and that has a small bump)
and the other stripped end of the wire to the negative end of the battery (the one that is
labeled with a negative sign and has no bump on it) as shown below:
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Once the circuit is complete, ask the student what he or she observes. The student
should note that the compass needle changes position. This happens because the needle
is responding to the magnetic field that is created by the electric current moving through
the wire. Have him or her disconnect one of the stripped ends of the wire from the
battery. What happens now? The compass returns to its original north-pointing position.
The "wire" affects only the small magnet when electricity is flowing through it. Once the
electric current stops flowing through the wire, the wire loses its magnetic properties.
Electromagnets:
The magnetic force produced by a small single wire, like the one you used above, is weak. But
we can use this basic concept to make a stronger magnetic force. For example, find a nail.
Attempt to attract a few metal paper clips to prove that the nail is not a magnet. Now wrap
the center of your wire around the nail ten times, leaving the ends free. Now connect the
stripped ends to the positive and negative ends of the battery as you did before. Now try to
pick up the paper clips. What happens? The nail acts like a magnet. The current in the wire
produced a magnetic field that magnetized the nail. However, when you disconnect the wire
from the battery and stop the electric current, the nail also stops being a magnet. Therefore, it
is a temporary magnet, not a permanent one like a bar magnet that is always magnetic. A
temporary magnet created by wrapping a wire around a magnetic object and running current
through the wire as you just did is called an electromagnet.
Changing the strength of electromagnets:
There are various ways to affect the strength of an electromagnet. Ask the student to guess
what some of these may be. Then discuss and explore the most common ones that follow:
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Changing what you use as the core of the electromagnet - meaning the object that you
wrap the wire around
Let the student try other objects as the core of his or her electromagnet. What if a
wooden pencil is used instead of a nail? Or a screw? Or a plastic pen? Or a crushed
aluminum can? Have the student wrap the wire around each core ten times and
compare the strength of each electromagnet by seeing how many small magnetic
objects each can pick up. He or she will find that objects made of magnetic metals
will all become electromagnets and that those objects made of iron create the
strongest ones. However, when the student uses material that is not magnetic like
wood or plastic for his or her core, he or she will find that the object will not
become a magnet at all.
Changing the number of turns or times that you wrap the wire around the core of the
electromagnet
Let the student experiment with various numbers of turns using the nail as the
core of his or her electromagnet. What if he or she used only one turn? How about
20? Or 100? The student can compare the strength of the magnet created in each
scenario in the same way as above. He or she will find that the more turns, the
stronger the electromagnet.
Changing the amount of current that travels through the wire
This factor is too dangerous to experiment with at home. However, tell the student
that stronger currents create stronger electromagnets.
Uses of electromagnets:
Electromagnets are at work in many familiar devices, such as doorbells, electric motors, and
speakers. Have the student research via the Internet or encyclopedias one of these devices or
another that he or she chooses that uses electromagnets. Have him or her discover how the
device works and the electromagnet’s role in it. Below are some links that have relatively
simple explanations for some of these devices:



How Stuff Works at http://home.howstuffworks.com/doorbell2.htm, describes a simple
buzzer doorbell as well as more complex models
Schoolscience at
http://www.schoolscience.co.uk/content/4/physics/copper/copch3pg1.html, describes a
basic electric motor
School for Champions at http://www.school-forchampions.com/science/electromagnetic_devices.htm, describes the inner workings of a
loudspeaker when you scroll down the page
Magnets produce electricity:
Tell the student that now you are going to explore the other half of the electricity-magnetism
relationship: how moving magnets create electricity. When a magnet and its magnetic field
are moved by a wire (or any other substance that conducts electricity), an electric current is
produced in the wire (or other conductive material). It doesn’t matter if the wire is physically
moved through the magnetic field or if the magnetic field is physically moved past the wire,
the result is the same.
The most common example of this phenomenon is a generator such as the ones used in
power plants that produce the electricity we use. Inside such power plants, there are large
magnets and large coils of copper wire. Either the coils of wire are moved past stationary
magnets, or the magnets are moved past stationary coils of wire. In both cases, the motion
produces a current in the wire -- and our electricity. Power plants use various sources of
power (water, steam, nuclear, etc.) to move the magnets or wire. If the student is interested,
have him or her research generators in encyclopedias or by using the Internet. How Stuff
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Works has a thorough description of a hydropower plant, which is powered by moving water,
and the generator used in it.
Review:
What is the important relationship between electricity and magnetism?
What is an electromagnet?
What are some factors that impact the strength of an electromagnet?
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Relate state of matter, contraction, and expansion to the motion of molecules.
Students should be able to differentiate molecular motion and arrangement in the three
states. They should also understand how heat correlates to molecular motion as well as
explain contraction and expansion in terms of molecular motion.
Tutorial:
For this tutorial, you will need the following:
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3 identical clear cups
Cold water, room temperature water, and hot water
Food coloring
A balloon
A measuring tape
Particles and the states of matter:
All matter is composed of atoms and molecules that are in constant motion. How fast the
particles are moving and how they are arranged determine the state of matter of a substance
as described below:
The particles in solids are very close together and have little space between them. The
particles are rigid and only vibrate or wiggle instead of moving from place to place.
The particles in liquids are more loosely arranged, although they still have little space
between them. The particles in liquids have higher energy than those in solids, and they
move from place to place by "flowing" or "sliding" by one another.
The particles in gases have significant space between them. The particles have even
more energy than those of liquids, and move around freely, colliding into one another.
Check out Purdue University’s Visualization and Problem Solving for General Chemistry
website at www.chem.purdue.edu/gchelp/atoms/states.html. It has great microscopic
representations of the particles in the three states of matter.
How heat impacts particle motion:
The motion of these molecules and atoms is impacted by heat. If heat is added to a
substance, its atoms and molecules will move faster. If heat is removed, the particles will
move slower. The following simple experiment will demonstrate this:
Get three identical clear cups. The cups should be filled with the same amount of water,
but the water in each should be at a different temperature. One should be filled with tap
water and placed in the freezer for 30 minutes so that it will be cold. The second should
be filled with tap water and left on the counter for 30 minutes so that it will be room
temperature. After the 30 minutes, the last cup should be filled with very hot water from
the tap.
Quickly and carefully add two drops of food coloring to each cup. Observe how long it
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8/12/2009
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takes for the color to spread through the water in each cup. Which took the shortest
amount of time? Which took the longest amount of time? Ask the student to think about
why this was the case. Guide him or her to the fact that the particles in the hot water
were moving the fastest and thus dispersed the color the quickest. Likewise, the
particles in the cold water were moving the slowest, and thus took the longest to
disperse the food coloring.
Expansion and contraction:
As heat increases and particles begin to move faster, they also need more space. Mercury in a
thermometer is a great example of this. When you take your temperature, you add heat to
the mercury in the base of the thermometer, causing the particles in it to move faster. As
they move faster, they need more space and the mercury expands, moving up the
thermometer to where you can read it. The reverse is also true. As heat is removed from a
substance, the particles begin to move slower and require less space. When you remove the
thermometer from a heat source, the particles begin to lose heat and begin to slow down their
movement. As they slow down, the particles in the mercury need less space and the mercury
contracts, moving down the thermometer. For a more detailed discussion of this, see the
website How Stuff Works at www.howstuffworks.com.
A party balloon can also illustrate this. Blow up a party balloon and tie off its end. Measure the
balloon’s diameter at the point that it is the largest. Put the balloon in the freezer for 15
minutes. Remove the balloon and measure its diameter again. What happened? The particles
in the air in the balloon got colder and slowed down their movement. Thus, they needed less
space so the balloon shrunk. If the balloon is left out in warmer air, its diameter will increase.
Phase changes:
As heat continues being added to a substance and its particles move faster, requiring more
space, the substance changes state. A solid will become a liquid, and a liquid a gas.
Eventually, as heat continues to be removed from a substance and its particles move slower,
requiring less space, the substance also changes state. A gas will become a liquid, and a liquid
a solid.
Review:
Look for examples of phase changes and expansion and contraction in daily life, such as the
thermometer discussed above. Have the student explain what is happening in these examples,
applying his or her knowledge of particle motion.
Review:
Describe the motion and arrangement of molecules in solids, liquids, and gases.
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8/12/2009