Build a Rubber Band Paddle Boat
Build your own bathtub or pool toy from simple craft materials in this fun activity! You will build a rubber-band-powered boat that can zip across the surface of the water after you wind up the rubber band.
- Rubber band
- Materials for the boat, such as:
- Cardboard (requires duct tape for waterproofing)
- Balsa wood
- Popsicle sticks (requires hot glue gun for assembly)
- Optional: Small pieces of foam to make the boat float better
- Hobby knife or scissors
- Bathtub or kiddie pool
- Fill your kiddie pool or bathtub so you are ready to test your boat!
- Depending on which materials you are using, you can watch video instructions on how to build your boat, or keep scrolling for written instructions.
- Make the hull of your boat.
- If you are using balsa wood or cardboard, start with a rectangular piece that is about 3 by 5 inches. Cut corners or round off one end of the boat. This will be the front.
- If you are using popsicle sticks, first score one by etching a line with the end of the scissors so you can more easily snap it in half, then glue the sticks together to make a frame, like the one pictured.
- Cut out a section for the paddle, approximately a 2-by-2-inch square (this step is not necessary if you built your frame from popsicle sticks).
- Make the paddle.
- If you are using cardboard or balsa wood, cut the piece you removed from the hull so it is narrower than the gap. This will ensure it has room to spin without getting stuck.
- If you are using popsicle sticks, cut another popsicle stick in half.
- If you are using cardboard, completely cover and seal both the hull and the paddle with duct tape to prevent them from getting wet.
- Stretch a rubber band across the gap in the hull. Slide the paddle through the rubber band, and twist it at least 20 times to wind it up. Hold the paddle in place so it does not unwind.
- Put your boat down in the water, release the paddle, and watch it go!How far does your boat go before it stops? If you wind the paddle up more, does the boat go farther?
- Optional: Glue some small pieces of foam to the bottom of your boat to make it float better. This is especially useful for boats made from popsicle sticks.
When you put the boat down in the water and released the paddle, the paddle should have spun, propelling the boat forward! The more times you wound up the paddle, the farther the boat should have gone.
In this project you built a miniature version of a paddle boat. In the 1800s, large steam-powered boats that could carry lots of people were propelled by large paddles. Today, smaller recreational boats are powered by people, who sit and use pedals to turn the paddles, just like riding a bike.
The paddle boat is a good way to demonstrate two different laws of physics. First, it demonstrates conservation of energy. When you twist up the rubber band, it stores elastic potential energy (the energy stored in a stretched material). When you release the rubber band, this potential energy is converted to kinetic energy (the energy of motion), and the boat moves forward.
Second, when the paddle spins, it pushes on the water, pushing the water backward. According to Newton's third law of motion, for every action there is an equal and opposite reaction. This means that the water pushes back on the paddle, pushing the entire boat forward.
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For Further Exploration
- Try improving the design of your boat's hull. Can you make a hull that is more streamlined and goes farther?
- Try to make your boat more waterproof so it can be left in the water for longer periods of time.
- Design a 3D printed boat instead of making one from craft materials.