June 23, 2004

Come-Back Drum

Scientists define energy as the ability to do work. Energy and work are both measured in the same units. Many people use the word power to mean the ability to do work. Scientists, however, define power as the measurement of the rate at which work is done, or at which energy is given up.

Imagine you can see a boulder sitting high upon the edge of a cliff. Imagine you can also see another boulder tumbling down the face of the cliff. Which of the boulders would you suppose contains energy?

Surprisingly, both boulders are examples of energy. The boulder sitting on the edge of the cliff has potential, or stored, energy. The boulder has the potential to fall; if allowed to fall, it has the ability to do work. If the boulder is pushed over the edge, the potential energy becomes kinetic energy. Kinetic energy is the energy of movement.

Explore energy by constructing this come-back drum. As the drum is rolled away from you, the rubber band inside it stores up the energy needed to drive it back again.

You will need—

• stiff paper
• scissors
• cellophane tape
• stiff cardboard
• pencil
• 4 paper clips
• 3-inch rubber band
• modeling clay
• colored pencils or felt-tipped pens

Procedure

1. Cut a piece of stiff paper to a measurement of 40 inches by 6 inches with scissors. Roll the paper into a cylinder of about 4 inches in diameter. Fix the seam with cellophane tape.
2. Stand the cylinder on a piece of stiff cardboard about 12 inches by 6 inches. Draw around the cylinder with a pencil. Use scissors to cut out the circle. Repeat the process to make another circle.
3. Attach one of the four paper clips to a 3-inch rubber band with cellophane tape as shown. Hook another paper clip through the one attached to the rubber band.
4. Mold a small ball of modeling clay around the second paper clip as shown. Then, using the point of the scissors, carefully make a small hole in the center of each cardboard circle.
5. Push one end of the rubber band through the hole you have made in one of the cardboard circles.
6. Thread a paper clip through the end of the rubber band and tape it to the circle.
7. Now tape the circle to the end of the cylinder. Use several small strips of cellophane tape to ensure a strong seal. Pull the spare end of the rubber band through the cylinder.
8. Push the spare end of the rubber band through the hole in the other circle and tape it to the cardboard. Then position the circle on the end of the cylinder and tape it carefully into place. You can decorate the drum with colored pencils or felt-tipped pens if you like.
9. Now put the drum onto a hard floor and roll it away from you. When it stops, it will begin to roll back toward you. You can wind up your drum so that it rolls along by itself if you turn it around and around in your hands for a few seconds.

Activity from More Science in Action: The Marshall Cavendish Guide to Projects and Experiments, Vol. 1: Forces of Nature by Laura Buller and Ron Taylor, is used by permission of Marshall Cavendish Corporation (www.marshallcavendish.com). © 1990 by Marshall Cavendish Corporation.

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