We got a plastic bottle and put a balloon on it.

Then we put it into a basin of hot water.
Don't look at our photo yet!
What do you think will happen?

Look! The balloon inflates.

This one has lots of hot air in it.
Why?
Hot air expands and takes up more space than cold air,
so it has nowhere to go, except up into the balloon.

 

Then we tried something else.
We'll show you what happens when we cool down hot air.
We got a bottle and put a balloon on top.
Next we put the bottle into a bucket of cold water.
Guess what will happen this time?

This is really exciting.
The ballon gets sucked back inside the bottle.

We are going to be scientists when we grow up.