# Cool Crush

Now with real, cool-crushing action! Watch out as the air pressure surrounding us all the time is more than enough to crush a plastic bottle with destructive power.

## Australian Curriculum links

• Science > Chemical Sciences > Year 5 > ACSSU077

## You'll need

• 1.25 L plastic soft drink bottle with a lid
• funnel
• 1 cup hot water
• large bowl half-filled with ice
• jug filled with cold water

## Try this

1. Unscrew the lid of the plastic bottle and use the funnel to pour a couple of tablespoons of the hot water into it. What happens to the bottle?
2. Let the bottle sit for two minutes so the water can warm the whole bottle then screw the lid back on.
3. Lay the bottle on its side in the bowl of ice and pour the cold water over the bottle.
4. Remove the bottle from the ice and unscrew the lid. What do you see and hear?

## What's happening?

Air is all around us and is pushing on us from all directions. Air pushes on other objects too and this pushing is called air pressure. We don’t notice air pressure, but it’s always there.

After the lid is screwed onto the bottle in step 2 of this experiment, the warm air inside the plastic bottle is pushing out on the sides of the bottle and the cooler air outside the bottle is pushing in. Warmer air has a greater pressure so the air inside the bottle is pushing harder than the outside air.

When cold water is poured over the bottle, the air inside the bottle cools down. Colder air has a lower pressure, so there is now a lower pressure exerted by the air inside the bottle. The air outside the bottle now has a higher pressure than the cold air inside the bottle and this high pressure crushes the bottle.

Unscrewing the lid allows air to move into the bottle and the air pressure inside and outside the bottle becomes the same.

The atmospheric pressure at sea level is 101.3 kilopascals (kPa) which is approximately 1 kilogram per square centimetre. That means that on every square centimetre of your body the air pressure is equal to the force of a 1 kilogram mass pressing down on you.

## Real world links

Sea level is usually the deepest you can be in the atmosphere and this is called ‘zero metres’. However there are a few exceptions including the Dead Sea between Israel and Jordan, which is 400 meters below sea level. The Dead Sea has an atmospheric pressure of 106.6kPa. This pressure is so high that the air filters out the sun’s harmful UV rays.