Introduction

Air is made from gas particles. They constantly move around at a high speed. When speeding around like this, the particles often collide with the walls of their containers. For example, the air particles in a balloon move around and hit the balloon’s walls. These collisions cause the balloon to stay inflated. We call this gas pressure.

There are two ways to affect gas pressure. One is to change the number of air particles. When you blow up a party balloon, you add more air particles to it. More gas particles hit the walls more often and the balloon’s pressure increases.

The second method to increase pressure is by raising the temperature. When it is warmer, the gas particles have more energy and move faster. If the particles move faster, they hit with the walls more often and the pressure increases. When decreasing the temperature by cooling, the gas pressure will decrease.

In this experiment we are going to look at what happens to the pressure inside a plastic bottle when you cool down the temperature.

What you will need

• 1 empty plastic bottle (a small bottle is enough, 500 ml or even smaller)
• Freezer

What to do

1. Remove the lid and put the empty plastic bottle in the sun or on the radiator to heat up a bit.
2. Close the lid tightly, so nor more air can move in or out of the bottle.
3. Put the bottle in the freezer and wait for one hour.
4. Collect the bottle from the freezer. What has happened to it? Take notes.
5. Now observe the bottle for a couple of minutes after taking it out of the freezer.

Questions

1. What happened to the bottle in the freezer?

2. Why did this happen? Look back at the introduction to find some clues.

3. What happened to the bottle after you took it out from the freezer?

4. Why did this happen? Look back at the introduction to find some clues.

5. Why was it important to close the lid tightly before putting the bottle into the freezer?

6. How could you improve this experiment?