OS10 Water Balloon Pressure


Water shot out of a hole in a can in an arc to the ground. The greater the water pressure behind the hole, the longer the arc. As the pressure fell, the arc shrank. Shouldn’t a hole in a water balloon act the same way?

filling the water balloon

Question: What happens to water coming out of a hole in a water balloon?




Water faucet in a large sink or hose

Block to set the water balloon on


Blow the balloon up about half way

Hold the neck closed and push on the balloon

How does the air behave?

hole in water balloon

It is easier to put a single hole in a partially blown up balloon. If the balloon is blown up too much, it will break.

Make a pin hole about half way down the balloon

Let the air go out of the hole

How does the balloon change as the air goes out?

Slide the neck of the balloon over the end of the faucet or hose [wetting it first makes this easier]

water balloon on faudet

Even if the mouth of the balloon is tight on the faucet, hold it on as you put water in the balloon.

Place the block so the balloon will sit on it as it fills up

Turn the water on slowly to fill the balloon

How does the water come out through the hole?

What happens to the hole?

Turn the water off when the balloon is about two thirds full

Observe how the water and the balloon act as the water goes out of the water balloon

Warning: Do NOT take the balloon off the faucet until almost all of the water is out of it‼!


How does air behave

When you push on an air filled balloon

When the air comes out of a hole in the balloon

Describe how water acts as you fill the water balloon

water balloon filling

Like the water from the hole in the can, water arcs out of the hole in the balloon

Describe what happens to the hole

Describe what happens as the water balloon empties

Describe what happens to the balloon as it fills and empties


Why does putting pressure on one part of an air filled balloon make another part bulge?

What happens to the balloon as you put pressure inside of it?

Why does the water arc get thicker as more water goes into the balloon?

water balloon with long water arc

The balloon stretches out and has elastic energy adding pressure to the water in the balloon making the water arc much bigger than the one from the can.

Compare the water arcs from the cans to the one from the balloon.

Why does the water arc from the balloon last so long?


What I Found Out:

I had some big round balloons. It was easy to blow one up just a little and poke a pin hole in it.

The balloon fit on the faucet in my bathroom sink tightly. I turned the water on a little.

For a few seconds water dripped out of the hole and ran down the balloon. After that the water arced out of the balloon. The balloon got bigger and so did the arc. Then both stopped changing.

I turned the water on a little harder. The balloon got a little bigger. The arc had more water in it but didn’t seem any bigger.

A balloon stretches as it gets bigger. A letter written on a balloon gets bigger as a balloon gets bigger. The hole got bigger so more water could get out.

I turned the water on a little more. The balloon got bigger slowly. The arc straightened out and had more water in it.

water balloon emptying

Taking the mouth of the balloon off the faucet before the balloon is empty lets the water form a geyser out of the mouth. This is only fun if you are outside on a hot day.

My sink was far too small. When the balloon got about eight inches across, the arc shot out over the sink and onto the floor.

When the water ran out of the can, the arc quickly shrank. The arc of water out of the balloon stayed up for a long time.

When I was done, I took the balloon off the faucet. Water shot up out of the mouth of the balloon like a geyser.

Only air and gravity put pressure on the water arcing out of the can. The balloon put pressure on the water inside of it making the arc large for a longer time and shooting the water out of the mouth when I took it off the faucet.