Spool-Racer: How Can a Rubber Band Transform (Change From one Form to Another) Energy?

Problem

How can a rubber band transform (change from one form to another) energy?

Materials

• rubber band (slightly longer than a thread spool)
• empty thread spool
• 2 round toothpicks
• masking tape
• metal washer (diameter must be smaller than that of the spool)

Procedure

1. Insert the rubber band through the hole in the spool.
2. Put one toothpick through the loop formed by the rubber band at one end of the spool.
3. Center the toothpick on the end of the spool, and secure the toothpick to the spool with tape.
4. At the other end of the spool, thread the rubber band through the hole in the washer.
5. Put the second toothpick through the loop in the rubber band. Do not attach it to the spool.
6. Hold the spool steady with one hand, and with the index finger of your free hand turn the unattached toothpick around and around in a clockwise direction to wind the rubber band tightly.
7. Place the spool on a flat, smooth surface such as the floor, and let go.
8. Observe the movement of the spool, rubber band, and toothpicks.

Results

As the rubber band unwinds, the spool turns, turning the toothpick taped to the spool. The unattached toothpick next to the washer does not turn and is dragged across the surface as the turning spool moves in a circular path.

Why?

Energy is the capacity to do work (the ability to move an object from one place to another). Energy never disappears; it is simply transformed (changed) from one form to another. There are two basic forms of energy: kinetic (energy of motion), and potential (stored energy). The rubber band had no energy before it was twisted. It took energy stored in the muscles of your body to wind the rubber band. As long as you held the stick, preventing the rubber band from turning, the energy was stored (potential). Releasing the stick allowed the rubber band to unwind; thus, the stored energy in the twisted rubber band was transformed into a form of kinetic energy called mechanical energy. Machines like the spool (a wheel) do not have energy and can only perform work (move from one place to another) if supplied with energy.

Let's Explore

1. Does the number of turns of the rubber band affect the results? Repeat the experiment exactly as before, counting the number of turns made on the rubber band. Then repeat the experiment twice more, first winding the rubber band more times, and then winding the rubber band fewer times.



2. Does the length of the rubber band affect the speed of the moving spool? Repeat the original experiment using different lengths of rubber bands. Record the rubber band lengths and your results. Science Fair Hint: Display the models made with the different lengths of rubber band.
3. Would a smaller or larger stick change the results? To discover the answer to this question, follow the original procedure, but use different-sized sticks such as long and short matches.

Show Time!

1. As any rubber band unwinds, its potential energy is changed to mechanical energy. Demonstrate this change by constructing and flying a rubber-band-powered model airplane. The model airplane can be displayed along with photographs taken during a test flight.
2. A can that rolls forward, stops, and mysteriously rolls backwards can be used to demonstrate the energy produced by an unwinding rubber band. Construct this can by punching two holes, ½ inch (1.3 cm) apart, in the center of the bottom of a metal can and two more similar holes in the plastic lid. Thread one rubber band through the holes in the can and a second rubber band through the holes in the lid. Tie the four looped ends of the rubber bands together with a piece of string, and in the same place tie a heavy bolt. Secure the lid on the can, and roll it forward. The weight of the bolt keeps the rubber bands in place, causing them to wind as the can rolls. The twisted bands unwind, causing the can to roll in the opposite direction.

Check It Out!

Work is accomplished when a force is applied to move an object from one place to another. Power is the rate of doing work. Horsepower is a unit commonly used to measure power. James Watt, a Scottish engineer, and inventor, coined the word horsepower. Find out how much power one horsepower equals, and why Mr. Watt used the term.

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Janice VanCleave's Machines
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