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AREAS OF SCIENCE
Mechanical Engineering
Design and build your own rubber band paddle boat.
Rubber band paddle boats are a fun bathtub or pool toy that you can build yourself. How do you make a boat that goes the fastest? Find out in this project as you build and test your own boat.


Paddle boats (Figure 1) were very common in the 1800s. They were usually powered by steam engines. While most modern boats use propellers instead of paddles, there are still smaller human-powered paddle boats with pedals like a bicycle (Figure 2), and even smaller rubber-band powered paddle boats that can be used as bathtub or pool toys (Figure 3).
paddle-boat

Figure 1. A full-sized paddle boat with a large paddle visible on the back of the boat. Wikimedia Commons user Zubro, CC BY-SA 3.0.

pedal-paddle-boat

Figure 2. Pedal-powered paddle boat (say that five times fast!). The paddles are under the boats, so you cannot see them in this picture.

wood-paddle-boat

Figure 3. A small toy paddle boat made from a rubber band and balsa wood.

The paddle boat in Figure 3 is powered by a rubber band. When you wind the rubber band up, it stores potential energy. When you release the rubber band, the paddle spins, pushing on the water, or exerting a force. Since the paddle pushes on the water, the water also pushes back on the paddle, pushing the boat forward (this is called Newton's third law of motion, or "for every action there is an equal and opposite reaction"). The potential energy stored in the rubber band is converted to kinetic energy, the energy of motion, as the boat moves forward.

Other forces also act on the paddle boat as it moves forward. The paddle boat's own weight pulls it down, but the buoyant force from the water makes it float. Friction from the water sliding past the boat, or drag, slows the boat down.

To make the boat go as fast as possible, you want to have the biggest push from the paddle, and the smallest amount of drag. There are different ways you can change these forces; for example, by changing the shape of the paddle or the hull (body) of the boat. You can also try making your boat from different materials. In this project you will use the engineering design process to design, test, and improve your boat. How fast will your boat go?

  • Paddle boat
  • Potential energy
  • Force
  • Newton's third law of motion
  • Kinetic energy
  • Weight
  • Buoyant force
  • Drag
  • Hull
  • What materials do you think you can use to build a paddle boat?
  • What forces act on a moving paddle boat?
  • How do you think you could change the shape of a paddle boat to make it go faster?
  • 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
  • Pencil
  • Ruler
  • Hobby knife or scissors
  • Bathtub or kiddie pool
  • Stopwatch or tape measure