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Remove both the ends from a pen so that the refill can slide freely through the barrel (Fig. 7.40). Fix the pen cap to the side of the barrel and attach a rubber band to the clip of the cap. Connect the free end of the rubber band to the refill using a safety pin. Stretch and release the rubber band. The refill shoots out, showing the conversion of elastic potential energy into kinetic energy. Repeat with different amounts of stretch, and observe how the distance travelled changes. Is there a relationship between the stretch and the distance travelled?
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The more you stretch the rubber band, the more elastic potential energy it stores, so the refill leaves faster and travels farther. You will find that a greater stretch gives a greater launch distance — the stored potential energy converts into more kinetic energy.
