Things you will need

  • Empty plastic bottle (optional cap)
  • balloon
  • push pin/scissors


Start by gathering an empty water bottle, balloon, and a pushpin or scisors for later.

To make sure that there is nothing wrong with the balloon, give it a test blow.

Then, take the deflated balloon and put it into the empty plastic bottle, covering the top of the bottle.

The goal is to blow up the balloon. But, you might notice that you cannot do this by simply blowing on the top of the balloon. This is because even though we cannot see it, the balloon is full of air helping to keep the pressure is equalized.

We can change that by poking or cutting a hole in the bottle.

Once there is a hole in the bottle, the balloon will inflate inside the bottle when you blow air into the top of it. This is because the air on the inside has a hold to escape from.

You can also fill up the balloon by sucking the air out of the bottle.

If you put your mouth over the hole that you cut out of the bottle, you can drink out the air and create a change in pressure. To equalize this pressure, the balloon will start to fill up as outside air sneaks in.

If you put the cap back on the water bottle, this will close off the balloon, and it will stay inflated because the pressure is equalized.

How you see this everyday

This is a fun experiment that you can repeat with the family, and is something that you might not notice happens with everyday objects like coffee cups.

You might notice that if you get a hot drink to go, the lid has 2 holes: one for you to drink out of, and another punched in it too.

Just like with the experiment, when you close off one hole and drink out the cup’s content, that second hole allows outside air to go into the cup to equalize pressure.