AIM OF THE EXPERIMENT: To see that energy can pass from one form into another.
MATERIALS: a rubber band tied in a loop.
MATERIALS: a rubber band tied in a loop.
Изображение
Hold the band against your forehead and remember how warm it is.
IMPORTANT: The forehead responds keenly to a change of temperature, so it can be used as a measuring instrument.
Hold the rubber between the thumb and forefinger of each hand and stretch it.
At once hold the rubber against your forehead.
RESULTS: The stretched rubber feels warm.
WHY? Rubber is made of molecules coiled up like springs. When we stretch the rubber, we straighten out the turns of the springs. The molecules coil back into springs when we let the rubber go. We used mechanical energy to stretch these springs, and the rubber used that energy to return to its earlier state. Part of the mechanical energy passed into heat energy (the energy of the motion of the molecules). Energy is needed to stretch the rubber, and energy is needed to bring it back to its original state. If nothing changes in the molecular structure of the rubber, stretching it and bringing it back take the same amount of energy. The energy passes from one form into another, but none of it is lost. This demonstrates the conservation of energy. METHOD:
IMPORTANT: The forehead responds keenly to a change of temperature, so it can be used as a measuring instrument.
Hold the rubber between the thumb and forefinger of each hand and stretch it.
At once hold the rubber against your forehead.
RESULTS: The stretched rubber feels warm.
WHY? Rubber is made of molecules coiled up like springs. When we stretch the rubber, we straighten out the turns of the springs. The molecules coil back into springs when we let the rubber go. We used mechanical energy to stretch these springs, and the rubber used that energy to return to its earlier state. Part of the mechanical energy passed into heat energy (the energy of the motion of the molecules). Energy is needed to stretch the rubber, and energy is needed to bring it back to its original state. If nothing changes in the molecular structure of the rubber, stretching it and bringing it back take the same amount of energy. The energy passes from one form into another, but none of it is lost. This demonstrates the conservation of energy. METHOD: