Rubber Band Regatta: Build a working paddle-wheel boat!

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Have you or your child ever seen a paddle boat up close? We’ve only seen the giant boat at Disney World’s Magic Kingdom, but it was really interesting!

The Paddle Boat STEM experiment demonstrates propulsion to kids by building a propeller that spins in the water, pushing the boat forward. It also demonstrates potential and kinetic energy, as you build up the paddles and let them go in the water.

Time to put on your captain’s hat and head to the sea!

How to make the Rubber Band Paddle Boat experiment

Supplies you will need

For this experiment, you’ll need:

Empty water bottle (leave the cap on!)
Popsicle sticks (4)
Hot glue gun
Duct tape
Plastic spoons (2)
Rubber band (good to have a few extra, in case they snap)

Supplies needed for the paddle-wheel boat experiment

Before you start

Have something handy to test your boat out, like a small pool of water in the backyard or filling your bathtub up.

Instructions

Here is how to do this experiment with your child:

Step 1: Hot glue two sets of popsicle sticks

Using your hot glue gun, glue two sets of popsicle sticks and be sure they are about the same length.

Two sets of popsicle sticks glued together

Step 2: Tape sticks to the side of the empty water bottle

Add the popsicle sticks to the side of the empty water bottle with a piece of duct tape.

Ensure the popsicle sticks are at about the same position on the water bottle and directly across from one another.

This next part is optional: you can add two cross beams to the popsicle sticks so they have a little more support and the sticks do not get too close to each other. One thing to keep in mind is, if you add these sticks, it will weigh down your boat a little.

Using duct tape to attach the popsicle sticks to the water bottle

Optional: adding cross beams to the popsicle sticks

Step 3: Cut spoons and glue

Cut the two plastic spoons about an inch down the stem from the spoon portion.

Using your hot glue gun, glue the handle of each spoon and stick them together. You will want one spoon facing up and the other spoon facing down.

Step 4: Place rubber band and spoon

At the end of the popsicle sticks, place the rubber band around the sticks so it’s perpendicular to the sticks.

Place the spoon in the middle of the rubber band and begin to wind the spoons in the opposite direction you want them to spin when in the water.

Run a quick check to ensure that the spoons will unwind in the right direction by letting them go for a second. If they turn with the concave portion of the spoon touching the water first, they’re in the right position!

Rubber band added to the popsicle sticks with the spoons inside the rubber band

The STEM behind the Rubber Band Paddle Boat experiment

This experiment teaches:

Propulsion
Buoyancy
Potential and kinetic energy

How it works

In this experiment, the empty water bottle is the floating boat and the popsicle sticks, rubber band, and spoons are the propulsion system.

The empty water bottle floats because of the air trapped inside, making it less dense than the water and causing it to be buoyant.

We build up potential energy in the rubber band and the spoons (the paddle) by twisting the spoons around until they are wound up tightly. The potential energy stored up in the spoons turns to kinetic energy once we place the boat in the water and let it go!

Propulsion

The rubber band and spoon paddle create thrust (force) that propels the boat forward. This act of driving the boat forward is called propulsion.

The key ingredient to the propulsion here is Newton’s Third Law of Motion. You know the one: for every action, there’s an equal and opposite reaction.

When the spoons (paddle) push water backward (action), the water pushes back on the spoons with an equal and opposite force (reaction).

This reaction force propels the paddle boat forward. We can see this in action by observing how much water the paddle displaces and how the boat moves in response.

Buoyancy

In this experiment, the empty water bottle with the cap still on is our boat that floats on the water.

Since the weight of the water bottle is less than its buoyant force, it floats. If the water bottle’s weight was more than its buoyant force, like if we added coins inside of the water bottle, it would sink.

Here is a great explanation of buoyancy and why some objects sink and others float.

Potential and kinetic energy

We can also see potential and kinetic energy at work in this experiment!

When we wind up the spoons by twisting them inside of the rubber band, we are building the potential energy of the boat.

They see how the rubber band stores potential energy (by twisting it) which is then converted to kinetic energy (movement) when it unwinds and propels the boat.

When we twist the plastic spoons around the rubber band, we are building up potential energy for the paddle boat.