Extreme Science: Penny Shine

What you will need:

  • Hot Wheels ™ race track
  • Two cars that travel at the same speed, or two marbles the same size and weight
  • Adult supervision


  1. Set up two identical tracks side by side as shown.
    figure 1
  2. Place a car (or your marbles) on each track.
  3. Release them both at the same time to see if they both reach the ends of the track at the same time. If not, try switching cars until you find two cars that will travel the same distance and angle of track at the same rate of speed.
  4. Add items underneath one of the tracks to make humps so that one car will have further to travel as well as having to go up and down several times. You will probably have to add a short piece of track to this side.
    figure 4
  5. Try placing your cars at one end again and, as before, release them at the same time to see if they both reach the other end at the same time. Before doing so, can you guess which car will win?
  6. Try adding more obstacles under the one track to make more humps to see at what point both vehicles will reach the other end at the same time, regardless of the length of track that each one has to cover.

What is going on?

Potential energy is defined as the “energy” that an object has because of its position, rather than its motion. For example, any object that you hold in your hand has potential energy, which will change to kinetic energy as soon as you release it and it drops to the ground. Similarly, your cars both have potential energy as you place them on the high end of the racetrack. As soon as you release them, this energy is now converted to kinetic energy as they race down the track due to the force of gravity pulling on them. As the cars travel across the level portion of track, their momentum will carry them for a distance. You will notice that they slow down as they travel across this portion of track as they loose energy on this section of track. By placing obstacles under the track and causing one of the cars to raise to a higher level, it will again be propelled faster as it goes down the other side due to its potential energy being converted into kinetic energy once again. Typically, this car will reach the other end faster, even though it has a farther distance to travel due to the fact that it is traveling at a higher rate of speed. At some point, adding more and more humps will cause the track to become too long and the cars will again reach the other end at the same time.

Try this:

See how many humps and how much more track you can add before your cars will both reach the other end at the same time. Does it matter if you make the humps higher than the original starting point? What happens if you make the humps at different heights?

Radical Rick

Extreme Science