Bathtub Science: Balloon-Powered Boat!

Set sail this summer with STEM! Add a little excitement and science to your bath or kiddie pool with this balloon-powered sponge boat. The get-up-and-go of this craft relies on Sir Isaac Newton’s Third Law of Motion: For every action, there is an equal and opposite reaction.

The air from the balloon rushes out to push the sponge boat forward in the opposite direction with an equal force.

The air is the push while the water is the pull.

Let’s put this scientific law into motion by crafting our sponge boat.

Here are the easy-to-follow instructions:

You will need:

Thick kitchen sponge

Balloon

5/8 diameter, 3” long piece of plastic tubing (easily cut at the hardware store)

Craft knife and scissors

Ruler

Bathtub or kiddie pool

First, on the short end of your sponge, find the middle and mark it.

This is a great way for your kiddos to practice their ruler skills. Chances are good that the sponge is not an exact cut so critical minds will be needed.

Measure 2” down on each of the long sides and mark those, too.

Next, using your ruler, match your marks to make 45° angles from the center for the “bow” of your boat. Cut it with a scissors to fashion.

Find the middle of your boat by measuring the halfway point from the tip of the bow to the back of the boat.

Using your craft knife, have an adult poke a vertical slit at the mark. 

Caution: the craft knife slips through the sponge easily, so keep all hands clear.

Stretch out your balloon (aka “motor) by blowing it up. Fill up your bathtub or kiddie pool.

Poke the end of the balloon through the balloon. Attach the plastic tube around it, just at the very tip. If you pull down too much, the balloon might break.

Blow up your balloon through the tube. Use your finger to block the air until your boat is ready to launch.

Off to the high seas!

Important notes: Make sure that the plastic tubing is angled toward the stern of the boat. Our tubing just happened to be bent in the direction thanks to the stock at the hardware store. Also, a drier sponge works better. Make sure to squeeze out the sponge each time.

Set sail with science this summer!