Hysteresis of Rubber

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Hysteresis in Rubber A rubber band is made of latex and rubber, unlike a spring, once stretched it does not return to its original shape. This is an example of hysteresis. By studying the relationship between the stretching and unstretching of the rubber band, the work done and the energy lost by the band can be calculated. The molecules in a rubber band are disordered, coiled up and entangled with one another. Natural rubber contains strands of molecules with very weak links between them and is only held together by this entanglement. If rubber bands were made from real rubber, the molecules would eventually uncoil which would cause the rubber to pull apart as they slide past each other. However, synthetic rubbers are now used. In synthetic rubbers, additives are used and so can create cross links between molecules. This causes the rubber band to have an elastic limit which is caused when the molecules’ motion is stopped by these cross links. The disorder in the rubber band is described as its entropy, so when there is a high level of disorder of the molecules, there will be a high entropy level. When stretching occurs, the molecules line up and they uncoil from their original structures. This causes the molecules to become more ordered and so lowers the entropy. Heat is then given out when entropy decreases and therefore energy is lost. So then, when the material is contracted, it should absorb heat. Also, when a rubber band is heated, it will be able to contract on its own. The molecules start to become more disordered and so make the rubber band shrink. When the stretching force is removed from the rubber band, the molecules find it hard to return to their original length because the structure of the rubber band has been altered. The stretching of the rubber band causes all the kinks and tangles to uncoil which then don’t return to their original

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