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Bath tub Rocket Science

for kids and adults. 100% safe.

To the uninitiated, this activity is nothing more than a fun artsy pass time that feels more like magic than science, more like chemistry than physics, but I assure you this is the best place to start with the basics for becoming a rocketeer, and you will see why.

First, let's keep our promise of 100% safety by removing the speed, the unpredictability and even the need for a big outdoor space or a clear blue sky. This activity belongs on the kitchen counter or even in the tub. It is contained, predictable and may find yourself a little cleaner when all is said and done.

Bath tub Rocket Science:

The soap propelled paper boat is a simple enough experiment that requires little prep and can be done anywhere there is water. You will need:

  • Cardboard is best, but regular paper can work but will not last long.

  • Pair of scissors

  • Dish soap

  • An earbud

  • Water

  • A shallow container ( or in a bath)

Step 1. Cut the cardboard into the shape of a boat about the size of a credit card.

Step 2. Cut out the propulsion section at the back as seen above. As you can see it is in the shape of a triangle with a small opening at the back. This is how propulsion works in rockets. Using a balloon to illustrate, you can observe that pressure is funneled through a small opening to create propulsion.

Step 3. Dip an ear bud in some dish soap, then dip it again inside the triangle of the boat. Then observe how it propels forwards. This is caused by the soap which acts like a surfactant and breaks apart the water tension. As the water molecules disperse, they are funneled though the narrow end to create thrust.


As we have just learnt about the basics of how thrust is created, let us try a few variations to create a longer lasting thrust without the need to keep dipping the ear bud in the "tank" i.e. the triangle.

A. We can cut out a bigger tank in the shape of a rectangle, gently dip more soap in and see how long our soap rocket can run for. Ideal for the tub.

B. Like balloons and rockets, there is a narrow opening followed by a funnel to direct the thrust. What if we placed the narrow opening in the middle of the boat and cut out the back of the boat in the shape of a funnel as you would see on a rocket? would this create more directional thrust or not make a difference? See below

C. Experiment with different funnel shapes. Want to make your boat rocket spin in circles, make sure the nozzle (narrow section) is on the side of the boat. When the soap is added, it should spin in place.

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