What you need：

a balloon    a bottle

a cup or bowl    hot water

What to do：

1. Put the balloon on the top of the bottle.

2. Put some hot water into the bowl.

3. Put the bottle in the bowl.

What happens？

The bottle blows up（吹起）the balloon.The hot water warms（加热）the air of the bottle.The hot air rushes into（沖进）the balloon. It blows up the balloon.