Week 16 - Heat vs Temperature, Volume, Conduction, Convection and Radiation

By now you know that adding or removing enough heat to a substance will cause it to change state. But long before a solid changes to a liquid, other physical changes will begin to happen to the solid. With each particle taking up more room, a solid that gains energy will expand (increase) in volume. When heat is withdrawn from a solid it will contract (get smaller).

A large solid like a slab of concrete does not expand or contract evenly. Areas closer to the heat source will heat, and therefore expand more rapidly than other areas of the solid. This uneven heating and cooling, expansion and contraction, of a solid causes large stresses in the slab and the solid begins to crack at these stress points.

Dishes and glasses may crack if they are heated or cooled too rapidly. For example, taking a warm glass out of the dishwasher and filling it with ice cubes can cause it break from the uneven expansion and contraction in the glass.

The volume of liquids and gases also increases when heat is added. In fact, the expansion of liquids will be larger than that found in solids and the greatest expansion is found in gases. Liquid filled thermometers work on the principle of the expansion or contraction of the alcohol or mercury within the hollow tube.

Weather systems are caused by the expansion and contraction of air. When air is warmed its volume increases and becomes less dense. Because it is less dense, and therefore lighter than the air around it, it rises. This is called buoyancy. Something has to take the place of the rising air, so heavier air from other areas flows in to take its place. We call that moving air - wind. Ballooning is an activity that is based on the concept of buoyancy. In fact, people have actually circled the Earth by balloon!

The liquid in the world's oceans is also affected by heating. Some parts of the ocean get more heat from the sun than other areas. These differences in temperature and salinity (the amount of salt in the water) cause ocean currents that affect the overall climate of the world. One of the great concerns about global warming is the increase in the volume of the oceans caused by the world's increase in the water's temperature. This increased volume will cause the level of the water to rise up and cover many of the small Pacific islands. Many of the world's cities are on a coastline as well, and these could also be flooded by the rising waters.

This is an Optional Activity 

ACTIVITY D: Changing the Volume of Gas by Changing its Temperature

In this activity, you will be changing the volume of air in a two litre pop bottle. In the first part of the experiment, you will heat the air in the bottle and then allow it to return to room temperature. In the second part, you will cool the air and then let it return to normal. These changes can be observed by watching the action of the bottle itself.

MATERIALS NEEDED

• 2 - 2 litre pop bottles (preferably with the labels removed) , try to find normal straight-sided bottles.
• 1 measuring cup
• 1 cup of very hot water
• freezer

Part One: Heating the Air

Parent supervision and assistance is necessary for this portion of the experiment.

1. Find a plastic 2 litre pop bottle.

2. Fill a measuring cup with 250 ml of very hot water and pour the water into the pop bottle.

3. Hold the bottle at the top and swirl the water around in the bottle. Be careful not to burn yourself.

4. Pour the water into the sink.

5. Immediately cap the pop bottle (so that no air can enter or leave the bottle) and place it on a counter.

6. Watch the bottle's behaviour for three minutes and record your observations below.

Part Two: Cooling the Air

1. Take a second pop bottle, remove the cap and place it on the counter.

2. Without squeezing the bottle, reseal the bottle with the cap.

3. Squeeze the bottle and record your observations.

4. What did the bottle feel like when you squeezed it?

5. What did it sound like when you squeezed it?

6. Next, remove the cap, and place the bottle in the freezer for about ten minutes (make sure the bottle isn't crushed in any way).

7. Remove the pop bottle and immediately screw on the cap so that no air can enter or leave the bottle.

8. Let the bottle rest on the counter for approximately another ten minutes.

9. Squeeze the bottle and record your observations.

10. What did the bottle feel like when you squeezed it?

11. What did it sound like when you squeezed it?

12. Lastly, bring it close to your ear and slowly open the cap.

13. What did you hear?