The Science Notebook
Heat - Part 1

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 On this page...
 All Matter is Made of Molecules
Molecules in a Solid
Molecules in a Liquid
Molecules in a Gas
Space Between Molecules

Observing a Gas Expand When Heated
Observing a Gas Contract When Cooled
Observing a Liquid Expand When Heated
Observing a Liquid Contract When Cooled
An Exception to the Rule
Observing a Solid Expand and Contract
Expansion and Contraction of Railroad Tracks
Expansion and Contraction of Power Lines
Solids Expanding and Contracting - Other Examples
An Exception to Expanding and Contracting in Solids


You may already know that matter is anything that has mass and takes up space.  You may also know that matter exists in three states on earth - solids, liquids and gases.  In these experiments, we will investigate the ways that heat affects matter. 


Many of the properties of solids, liquids and gases may be better understood when you know how the molecules of each of these states of matter behaves. These next few experiments will illustrate how molecules behave in solids, liquids and gases.

All Matter is Made of Molecules

Materials Needed: A strong smelling substance such as perfume or cologne.

Procedure: Place the perfume or cologne container on one side of a room.  Open it and move to the other side of the room.  How long does it take for you to smell the substance from the other side of the room?

What Happened: After a short period of time, you were probably able to smell the substance, even though you were not able to see anything in the air.

All matter is made up of tiny particles called “molecules”.  These molecules are so small that they cannot be seen even with the most powerful light microscopes.  There is a special kind of microscope called the electron microscope that can magnify things many thousands of times their actual size.  But even with the electron microscope, the largest molecules look a little like fuzzy blobs.

The substance you smelled, like all other matter, is made up of molecules.  Some of these molecules broke away from the surface of the liquid.  We say that they evaporated from the surface.  These molecules then spread throughout the room by a process called diffusion.  Even though you could not see them, you knew they were there, because your nose is capable of detecting the odor of only a very few molecules.

In the next few experiments, we will make “models” of molecules in solids, liquids and gases.  Models in science usually can’t show us all we would like to see, but they can be helpful.  For example, a plastic model airplane you assemble from a kit will show what the real airplane looks like, so you can use it to learn a little something about how a real plane is put together.  However, this kind of model isn’t made to fly, so it might not be as useful as a gas powered model plane in helping you to understand how a plane flies. Scientists often use models to better understand things that are too large, too small, too fast, or too slow to observe in nature.  Molecules are far too small to be easily seen, even with the most powerful electron microscopes, but models can help us understand how they behave in the different states of matter. 

Our models will use sugar crystals to represent molecules.  Sugar crystals don’t really look line molecules, but they can give us some idea how the molecules behave.

Molecules in a Solid

You may have learned that a solid always has a definite volume and shape.  If you mold a lump of clay into a ball, it keeps that shape.  If you cut a star from a piece of wood, it keeps the shape of the star.  If left alone, the clay and the wood will not change in either shape or volume.

Solids keep their shape and volume because the molecules in a solid are strongly attracted to each other in much the same was as strong magnets are attracted to each other.  Because molecules are so strongly attracted, they cannot move around very much at all.   It is almost as if each molecule is tied to all the others around it, so the object cannot change shape.

CAUTION: Hot steam can cause serious burns!  Do this experiment only with adult supervision and be sure to use an oven mitt or potholder to protect your hands.

Materials Needed: Sugar; metal spoon; oven mitt or potholder; small metal pot; water; stove.

Procedure: Bring a cup or so of water to boil on the stove.  Place a spoonful of sugar over the steam from the boiling water for about a minute.  You don’t want to get the sugar hot enough to melt.  Instead, you just want it to be exposed to the steam.

Allow the spoon to cool down to room temperature.  Hold the spoon over a sink or trashcan and slowly turn it over.  What happens? 

What Happened: The steam caused the sugar crystals to stick together.  If sugar is left exposed to the air for any length of time, it will absorb water in the air, and will “clump up” or stick together on it’s own.  The only thing the steam did was to make this process go a little faster.

When sugar crystals stick together, they behave a little like molecules in a solid.  In a solid, molecules are not free to move around since they are strongly attracted to one another.  However, unlike sugar crystals, molecules in a solid vibrate, or move back and forth in place, but their attraction to each other is strong enough to keep them from moving around each other.  This is why a solid keeps a definite shape. 

Going Further: Another way of seeing this is to imagine that Lego ® blocks are molecules. When you snap them in place, they are held to all the other blocks to which they are attached, and they cannot move.  The points where the blocks fasten together represent the attraction between the molecules.

What our models cannot show easily is that even though the molecules in a solid are not able to move around, they do vibrate in place.

Molecules in a Liquid

Liquids have a definite volume, but not a definite shape.  If you pour a liquid into any container, gravity will pull the liquid to the bottom of the container, and the liquid will take on the shape of that container.

Liquids behave like this because molecules in a liquid are attracted to one another, although not as strongly as they are in a solid.  You can imagine this attraction being something like that of very weak magnets, rather than strong ones.  The attraction of molecules in a liquid causes the molecules to stay close to each other and not wander off, but the attraction is not so strong that they “stick” together as they would in a solid.  The molecules are free to move around each other.

Materials Needed: Sugar; two cups; clean paper.

Procedure: Fill one of the cups with sugar.  Now, pour the sugar into the other cup.  Do you see how the sugar pours a little like a liquid?

Next, pour the sugar out onto a piece of clean paper.  What does the sugar do?

What Happened: The sugar crystals behaved somewhat like molecules in a liquid.  When you poured the sugar into a cup, it filled the cup just like a liquid would.  When you poured the sugar onto the paper, it spread out almost like a liquid, but not quite.  A liquid would not pour into a heap in the center like the sugar, but this just shows us that our model isn’t perfect.  The sugar crystals are shaped like small blocks, and so they “catch” one another and tend to pile up.    

Another weakness of our model is that molecules in a liquid are attracted to one another, and the sugar crystals are not.  The crystals fill the cup and stay together because of the force of gravity alone. In fact, when you poured the sugar onto the paper, you probably saw that some of the individual grains along the edge of the paper moved away from the rest.  In a liquid, the molecules won’t move apart like that because of the weak attraction between them.

Going Further: Another model for liquids may be made of M&M’s ®, Reese’s Pieces ®, or similar candy.  These candies are rounded and smooth so the candy “molecules” will move against each other better than sugar crystals when you pour them out.  It’s also a good excuse to help yourself to a treat - all in the name of science, of course!

Molecules in a Gas

Gases do not have either a definite shape or a definite volume.  If air is in a bottle, it fills the whole bottle and takes on the shape of that bottle.

Gases behave like this because molecules in a gas are constantly in motion.  They are also much more spread out than molecules in a solid or a liquid.  Because of this, the attraction between molecules in a gas is not strong enough to hold them together.

Materials Needed: Your imagination; sugar; a spoon.

Procedure: Scoop up a spoonful of sugar.  Imagine you are on the International Space Station and you are weightless.  Based on what you’ve seen with the astronauts, what would happen if you were holding this spoon on the Station?

Now take the spoon outside and throw the sugar as high into the air as you can.  What happens to the sugar?

What Happened:  If you were inside the Space Station, the individual sugar crystals would have left the spoon and floated off in all directions.  After a while, sugar crystals would have been all over the place.  When you threw the sugar in the air, you could see the crystals spread out just as they would in the Station, but only for a very short period of time, since gravity quickly pulled them back to the ground.

Sugar on the International Space Station would behave exactly like molecules in a gas.  Molecules in a gas are much farther apart than in a liquid or a solid, and they have very little attraction for each other.  Because of this, molecules in a gas will spread apart until they have filled whatever container they happen to be in.  That’s why a bottle will never be “half full” of air. 

A gas will always spread out to fill up whatever space it has.

Going Further: Another way of making a model of gas molecules is to use a fine powder, such as baby powder, or flour.  Take a spoonful outside on a calm day and throw it into the air.  Because the particles are much smaller and lighter than sugar crystals, air resistance slows their fall, and you can see them spread out much better than the sugar. If you could see the individual molecules of gas in a container, they might look something like this powdery cloud.

Space Between Molecules

In the last few experiments, you have used particles of sugar to represent molecules.  You may have noticed when you used sugar to model a liquid, that there were spaces between the sugar crystals.  Even though we cannot see the spaces between molecules in a liquid, they are still there, and other molecules will fit in these spaces.
Materials Needed: Liquid measuring cup (If you are using metric units, substitute a 250 ml measurer); 1 liter (1 quart) clear glass or plastic container; tape; salt; rice; water; alcohol.

Procedure:   The success of this experiment depends on your being very careful to measure exactly one cup.  Each time you measure, be very careful to fill the cup to exactly the same level!

Fill the measuring cup with 1 cup (125 ml) of water.  Being careful not to spill any, pour the water into the container.  Carefully measure and add a second cup (or 125 ml) of water. Place a piece of tape on the container to mark the water level in the jar.  Pour out the water and dry the inside of the container completely. You now have a jar that will serve as a two cup measuring cup (or if using metric units, a 250 ml measuring device)..

Measure one cup (or 125 ml by volume) of rice and pour it in the container.  Measure one cup (or 125 ml by volume) of salt and add it to the rice.  Shake the container gently a few times.  Do the rice and salt come up to the two cup (or 250 ml) mark on the tape?  Why or why not? Empty the rice and salt and wipe out the container.

Next, measure one cup (or 250 ml) of water and pour it in the container.  Then measure one cup (or 250 ml) of alcohol and add it to the water.  Stir and remove the spoon.  Be careful not to lose any liquid. Observe the level of the liquid.  Does the liquid come up to the two cup mark?

What Happened: When you combined one cup of rice and one cup of salt, you got far less than two cups total because much of the salt was able to fit in the spaces between the grains of rice.  This should not have been surprising.  The rice and salt were crude models for molecules of two different sizes, and this model allowed you to see how molecules of one substance could fit in the spaces between the molecules of another substance.

When you mixed one cup of alcohol with one cup of water, there was slightly less than two cups of liquid.  The alcohol molecules are larger than the water molecules, so when the alcohol and water were mixed together, some of the water molecules were able to fit in between the larger alcohol molecules.  This time, you were dealing with actual molecules of water and alcohol.  While you obviously could not see the space between the molecules, you could see the effect of that space.


All matter is affected by heating and cooling.  With a very few exceptions, when any matter is heated, it will expand.  When it  is cooled, it will contract. 

Observing a Gas Expand When Heated


CAUTION: Hot steam can cause serious burns!  Do this experiment only with adult supervision, and be sure to use an oven mitt or potholder to protect your hands.

Materials Needed: Glass bottle with a narrow neck; balloon; small pot; water; stove; oven mitts or potholders.

Procedure:   Place the neck of the balloon over the mouth of the bottle.  Put about 6 cm (2 in) of water in the bottom of the pot and place the bottle and balloon in the pot.  Heat the water slowly over the stove. You do not need to heat the water to boiling.  What happens to the balloon?

Remove the bottle and allow it to cool.  What happens to the balloon now?

What Happened: When the air inside the bottle was heated by the hot water, it expanded. As the air expanded, some was pushed into the balloon causing it to expand slightly.  When the air inside the bottle cooled, it contracted and the balloon shrank.

Observing a Gas Contract When Cooled

Just as you saw a gas expand when heated, you can see how it contracts when cooled using the same material as in the last experiment.

CAUTION: Hot steam can cause serious burns!  Do this experiment only with an adult, and be sure to use an oven mitt or potholder to protect your hands.

Materials Needed: Glass bottle with a narrow neck; balloon; small pot; water; stove; two oven mitts.

Procedure: Place a couple of inches of water in the bottom of the pot and place the bottle in the pot.  Heat the water to almost boiling.  Then, using the oven mitts, remove the bottle and quickly place the balloon over the neck.  Allow the bottle to cool and observe the balloon as the bottle cools.

What Happened: As the air inside the bottle cooled, it contracted.  This caused the balloon to be drawn into the bottle.

Observing a Liquid Expand When Heated

CAUTION: Hot steam can cause serious burns!  Do this experiment only with adult supervision, and be sure to use an oven mitt or potholder to protect your hands.

Materials Needed: Glass soft drink bottle; water; food coloring (or instant coffee or powdered fruit drink mix); small pot; water; stove.

Procedure:   Put a little food coloring or a pinch of coffee or fruit drink mix in the bottle.  Fill the bottle completely with cool tap water.  Place a couple of inches of water in the bottom of the pot and carefully place the bottle in the pot, being careful not to spill any of the water.  Slowly heat the water in the pot almost to boiling and observe what happens to the water in the bottle.

What Happened: As the water inside the bottle was warmed, it began to expand.  The bottle could no longer hold all of the water and the water began to “bulge” from the top. Some may have even spilled out.

Observing a Liquid Contract When Cooled

CAUTION: Hot tap water can cause serious burns!  Do this experiment with adult supervision, and be sure to use an oven mitt or potholder to protect your hands.

Materials Needed: Glass or plastic soft drink bottle; hot tap water; oven mitts or potholders.

Procedure: Fill the bottle completely to the top with hot tap water.  Try to get as few bubbles in the water as possible.  Allow the bottle to cool where it will not be disturbed.  Be careful not to spill any of the water.  After the bottle has cooled to room temperature, observe the level of the water in the bottle.

What Happened: The water level was slightly below full.  As the water cooled, it contracted causing the water level to drop.  However, there may also be another effect here as well.  If you used water with a lot of bubbles, those bubbles also took up a part of the volume inside the bottles.  As the bubbles eventually floated to the top, they would have decreased the volume slightly.  Can you think of some way to insure that what you are seeing is not a result of the bubbles?

A Major Exception to the Rule

The general rule that has already been stated is that matter expands when heated and contracts when cooled, but there are a few exceptions.  The most important exception is water when it freezes.

Materials Needed: Plastic soft drink bottle with screw-on cap; water; newspaper; grocery bag.
Procedure:   Fill the bottle to the top with water and replace the cap.  Wrap the bottle in several layers of newspaper and place the bottle and paper in the bag.  Put the bag in the freezer and leave it there until the water freezes.

Remove the bag and paper and examine the bottle.  What do you see?

What Happened: The bottle was shattered or very swollen.  When water is cooled, whether as a gas (water vapor), a liquid, or a solid, it will contract.  The one major exception to this is when water reaches the freezing point and changes from liquid water to ice.  At that point, the water expands, rather than contracts.  This expansion caused the bottle to break.  

The reason water behaves this way has to do with the shape of it’s molecules. When water freezes into ice, it’s molecules line up in a certain way, and when they do, they take up more space than they did as a liquid.  It is almost as if the molecules elbow each other out of the way, and this causes the ice to take up more space than the liquid water.

Once the water freezes and gets colder than the freezing point ( 0º C or 32º F), it begins to contract again.  The only time water expands when cooled is at the point where it freezes.  However, the fact that water expands when it freezes is very important in nature. For example, one of the ways that rocks are broken down into soil is by water freezing in the cracks of rocks.  When the frozen water expands, it has enough force to cause the rock to split or break into smaller and smaller pieces. 

Observing a Solid Expand and Contract

CAUTION!  Always be careful to follow all safety precautions when using fire, and use with adult supervision only!  Keep your alcohol lamp or candle in an aluminum pie pan, and keep the flame at least three feet away from anything that can burn, unless otherwise instructed.

Materials Needed: Wire coat hanger; wire cutters; sandpaper; straight pin; coffee stirrer or broom straw; tape; books; candle or alcohol lamp with safety holder.

Procedure:   Using the wire cutters, cut a rod from the long bottom section of a wire coat hanger.  Keep this wire as straight as possible.  Use the sandpaper to sand the paint off the wire.  (You are going to heat this wire, and you need to remove the paint to avoid fumes from burning paint!)

Cut a section of the coffee stirrer or broom straw about 3 inches long.  Push the straight pin through the middle of this section.  The straight pin should fit snugly.  If it doesn’t, use a small piece of tape to hold it in place.

Set up the rod, pin, books and heat source as shown.  Make sure that the end of the rod away from the pointer is firmly against a book, and that the rest of the rod is touching only the pin, and not the surface of the books.

Heat the rod using your heat source, and observe what happens to the pointer.  Remove the heat source without disturbing the rod and watch what happens as the rod cools.
What Happened: As the rod was heated, it began to expand.  Since one end of the rod was against the book, it could expand in one direction only.  As it expanded, the rod moved over the pin, causing the pin to roll slightly.  Although the pin may not have rolled more than a quarter turn, the pointer allowed you to see this motion very clearly.  As the rod cooled, it contracted and moved the pin and pointer back to where they started.

We have seen that solids expand when heated and contract when cooled. Engineers who design roads, buildings, towers, and other large structures must know how much a substance will expand or contract over the range of temperatures it is expected to encounter.  The engineers then have to design the structure to prevent damage from expansion or contraction.  These next experiments will have you to examine some of these structures on a hot day in summer and a cold day in winter.  They could become part of a science project on heating and cooling.

Expansion and Contraction of Railroad Tracks

Raildroad Track Expansion Joint
(Original Photo Source - Wikimedia Commons)

CAUTION: Always be extremely careful around railroad tracks.  You should never be on tracks where you cannot immediately leave the tracks for safety.  You should also be able to see far down the tracks in both directions.  Do not attempt this on a bridge, trestle, or steep grade.  Do this only with adult assistance.

Materials Needed: Camera (optional); thermometer; ruler; notebook; railroad tracks.

Procedure:   Pick a very hot and a very cold day to do this. 

Walk along a railroad track until you find a place where two rails are joined together.  You should see a small gap between the rails where they are fastened together.  This gap is called an “expansion joint”.  Some newer tracks have rails that are continuously welded together and do not use expansion joints.  If you walk for some distance and do not see a gap between two rails, the tracks you are looking at are probably of this kind.  If possible, you should try to locate an older track, or even one that is no longer in use.  Such track will be more likely to have expansion joints.

If you are able to locate an expansion joint, measure and write down the outside temperature, along with the date and the time.  Also, measure and record the size of the gap.  The millimeter scale is probably the best scale to use. If you have a camera (particularly if this is part of a science project) take a picture of the joint.  It is a good idea to take this picture with the ruler in place.  Save your notes.

If you did this on a hot day, repeat it on a cold day, or vice versa.  Can you measure any difference in the size of the gap?

What Happened: The gap is slightly narrower on a hot day, because the rail sections on either side of the gap expand with the increased heat.  If expansion joints were not put in place and the rails were placed tightly together on a cold day, when they were warmed by the sun, they would buckle and perhaps come loose.  If the rails were put down tightly on a hot day, they would pull apart in cooler weather. Either could cause a very serious accident.

Expansion and Contraction of Power Lines

CAUTION: There is no need for you to get close to the lines to do this experiment, but you should still be careful. Do this only with adult assistance.
Materials Needed: Camera; thermometer; notebook; power lines between two poles or towers.
Procedure:   This experiment, just like the last, will need to be done on both a very cold and a very hot day.

On a very hot or cold day, locate power lines near your home hanging between two poles or towers.  Notice how much the lines sag.  Measure and record the temperature as well as the date and time.  Select a good spot to take a picture of the lines.  Carefully note exactly where you make this picture in your notebook, including any zoom setting and the center of your photo.  Make sure that you will be able to return to the exact spot several months from now.  

Return to the same spot when the weather is much hotter or colder, depending on when you did this the first time.  Again, measure and record the temperature, date and time.  Take another picture of the wires using the same zoom settings and center point as before.

Compare the two pictures.  What do you see?

What Happened: The wires sagged much less in cold weather.  Wire, like all other solids, expands when it is warmed and contracts when it is cooled.  In hotter weather, it will expand more, causing the wires to sag more.

When power or phone lines are strung, they are always sagged to allow for expansion and contraction.  If they were to be strung too tight, they could snap when they contract in colder weather.

Solids Expanding and Contracting - Other Examples

Materials Needed: Camera (optional); thermometer; ruler; notebook; various locations (See Procedure)

Procedure:   There are many other examples of expansion and contraction you may observe.  Some suggestions are sidewalks, concrete roads, bridges, and tower guy lines. Can you find others?  See if you can identify expansion joints or other structures used to prevent damage from expanding and contracting in each.  If you are doing this as part of a science project, do this on both a cold day and a hot one, and be sure to record your results.

An Exception to Expanding and Contracting in Solids

As we have seen, solids usually expand when heated and contract when cooled.  However, some solids don’t always behave according to this rule, as this experiment will show.

Materials Needed: Small cardboard box; rubber band; pushpin; small weight; string; hand held hair dryer.

Procedure:   Turn the box on its side as shown.  Place the pushpin in the top edge of the box and hang the rubber band over the pushpin.  (If you can’t get the pushpin to hold firmly, try taping the rubber band.)

Tie a small weight to the other end of the rubber band.  The weight should be heavy enough to stretch the rubber band, but not enough to break it.

Set the dryer on it’s hottest setting and heat the rubber band.  Note what happens to the rubber band. 

What Happened: Instead of expanding as we would have expected, the rubber band contracted and lifted the weight.  Molecules of rubber are long and twisted, something like a loose spring.  Rubber molecules compress when they are heated, causing them to draw together like a tighter spring.  When all of the molecules do this, the rubber band contracts.

There's more "hot" stuff on the Heat - Part 2 page!

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