Wind Up Racer

Demonstrate potential and kinetic energy the easy way

Print this Experiment

Finding creative, hands-on ways to demonstrate the difference between potential and kinetic energy can be difficult. With some simple household items and a little creativity, the Wind Up Racer will have you racing a spool across the room in no time!


Experiment Videos

Here's What You'll Need

  • Spool
  • Toothpick
  • Rubber band
  • Tape
  • Metal washer
  • Pencil

Let's Try It

  1. Hook one end of the rubber band around the toothpick.  Push the end of the toothpick with the rubber band through the center of the spool in order to thread the rubber band through. Remove the toothpick, but keep the rubber band threaded through the center with a bit sticking out on each end.

  2. Break the toothpick so that it is a little shorter than the diameter of the spool.

  3. Put the toothpick through one end of the rubber band and pull the rubber band taut so that the toothpick lays flat on one end of the spool.

  4. Tape the toothpick to the end of the spool, holding it in place.

  5. Pull the other end of the rubber band through the center of a washer.

  6. Stick the pencil through the rubber band next to the washer and twirl the pencil. This will twist the rubber band.

  7. Once the rubber band is wound up, put the spool down on its side on a smooth surface and let it go!

How Does It Work

When you twist the rubber band with the pencil, you stretch the rubber band and wind it up. This winding and stretching creates and stores potential energy. Potential energy is energy that has the ability to do work in the future, but is not currently performing any work. The more twisting you apply to the rubber band, the more potential energy you create. When you put the spool down on a surface, the rubber band unwinds and converts the potential energy into kinetic energy, the energy of a moving object, as the spool rolls across the surface.

Science Fair Connection

Creating a Wind Up Races is pretty cool, but it isn’t a science fair project.  You can create a science fair project by identifying a variable, or something that changes, in this experiment.  Let’s take a look at some of the variable options that might work:

  • Try testing different spool sizes. Which size rolls fastest? Which size rolls the farthest?

That’s just an idea, but you aren’t limited to that! Try coming up with different ideas of variables and give them a try. Remember, you can only change one thing at a time.  If you are testing a different size of spool, make sure that the other factors are remaining the same.

Browse more experiments by concept: