Rubber Band Heat Engine (page 2)
The work performed by your heat engine in this experiment is the movement of the weight by the expansion and contraction of the rubber band.
When the rubber band is heated, heat energy from the surrounding environment goes into the molecules of the rubber band and causes them to vibrate. The more the molecules vibrate, the more they collide with their neighbors, putting tiny kinks and bends into each chain. This causes the rubber band to contract.
When the rubber band is cooled with the ice, its chain-like molecular structure becomes more rigid, or stiff—meaning the molecules aren’t vibrating and colliding with each other. This prevents the chains of rubber molecules from contracting, and the “chains” are allowed to loosen up— that is, the molecular bonds become longer and the rubber band gets stretched out.
Get another rubber band. Without stretching it, touch it to your lip. How does it feel? What do you notice about its temperature? Now, stretch it out quickly and bring it to your lip while it’s still stretched. You should notice that it’s warmer, because you performed work on the rubber band. The energy you gave the rubber band got converted to heat.
Wait a few seconds with the rubber band still stretched out. Quickly release the tension and let it assume its normal shape. Bring it to your lips now. It should feel cold, since it absorbed thermal energy!
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