Cool crush

Science concept

Air pressure changes with temperature.

Special instructions

Now with real cool crushing action! The air pressure surrounding us all the time is more than enough to crush this plastic bottle.

Teachers should conduct their own risk assessment of this activity.

Class time required: 15 minutes

Materials

• 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

What to do

1. Unscrew the lid of the plastic bottle and use the funnel to pour the hot water into it.
2. Let the bottle sit for two minutes so the water can warm the whole bottle then screw the lid back on.
3. Lie the bottle on its side in the bowl of ice and pour the cold water over the bottle.

What happened to the bottle?
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 top of 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.