Balloon in the Bottle – A Demonstration About Air

How hard would it be to inflate a balloon inside of a bottle? Would you believe it is impossible unless you know the science of air?

Place a deflated balloon inside of a plastic bottle and stretch the mouth of the balloon over the bottle top. Start blowing. Can you blow up the balloon?

Now, have an adult punch a small hole in the side of the bottle and try blowing up the balloon again.

The balloon will inflate inside of the bottle. Now plug up the hole with your finger. The balloon will stay inflated.

How does this work?

Balloon in a Bottle

The balloon won’t inflate much the first time because the bottle is already filled with air. There’s no room for the balloon to expand inside the bottle. However, when you punch a hole in the bottle, the air molecules in the bottle have an exit. They’re p

ushed out as the balloon fills the space inside. As long as you plug the hole, the balloon stays inflated. When you take your thumb off the hole, outside air flows back into the bottle as the balloon collapses.

Try this! Inflate the balloon in the bottle again and cover the nail hole with your thumb. Pour water into the balloon while keeping your thumb over the hole. Go outside or hold the bottle over a sink before you remove your thumb. Watch out for that stream of water gushing out of the bottle top! You might decide to hand a full water-balloon-bottle to a friend and just “forget” to tell them about the hole.


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