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InTENSE Science: Build a Tension-Powered Car

Be a Scientist

If you loop a rubber band around your index fingers, and pull your fingers apart, you will feel a pulling force between your fingers as the band becomes more difficult to stretch. This force is called tension. Let’s see how we can use tension to power a mini-car.


  • one clean 1-litre milk carton
  • one bulldog paperclip
  • two skewers, cut to 14 cm in length
  • four Styrofoam balls
  • rubber bands
  • weight (such as a set of keys)
  • scissors, tape, and glue
  • construction paper and decorations

What to do

  1. Lay your carton (the car body) on its side. On the side facing up, cut two openings, leaving a strip of cardboard in the middle for support.
  2. Turn the carton over, and cut a slit where the carton top meets its side.
  3. Insert the bulldog clip in the slit, and unfold the handles so they lie flat. Secure a rubber band to the inside handle.
  4. Pierce two holes in each side of the carton to hold the skewers (the car’s axels). Insert one skewer through the holes in the front of the car, and the other through the holes in the back — make sure the skewers turn freely.
  5. Pierce the centre of one Styrofoam ball (one of the car’s wheels), and glue it to one end of the front skewer. Pierce another Styrofoam ball, and glue it to the other end of the front skewer.
  6. Tie the loose end of the rubber band to the centre of the rear skewer. If the rubber band is too short to reach, and still remain loose, add one more.
  7. Repeat step 5 for the rear skewer.
  8. Decorate your car with construction paper and whatever else you like.

Now it’s time to race your car. Wind its rear wheels backwards — the rubber band will wrap around the axel. Keeping hold of the wheels, place your car on the floor. Release the wheels and — zoom! — the car should speed forward. Add a bit of weight, like a set of keys, to the back of your car to help it move farther.

What happened?

When you wind up the rear wheels of your car, the rubber band wraps around the axle, adding tension to the rubber band. When you release the wheels, you release the tension and the rubber band pulls itself back to its original shape. The rubber band unwinding from the car’s axle causes the axel and wheels to turn, which moves the car forward.


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