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# Hysteresis graph for an elastic band watch

1. In the graph for hysteresis, the area inside the loop represents heat energy lost by the rubber band and area underneath the lower loop represents energy left in the band after loading/unloading.
But if Work done = Force * extension, shouldn't the rubber band gain energy as work is being doen on it?
2. (Original post by Kolasinac138)
In the graph for hysteresis, the area inside the loop represents heat energy lost by the rubber band and area underneath the lower loop represents energy left in the band after loading/unloading.
But if Work done = Force * extension, shouldn't the rubber band gain energy as work is being doen on it?
The hysteresis loop must be interpreted as a time-bounded function and in the work = force x extension statement, energy losses over time are not taken into account and so will not fit all observations. i.e. the hysteresis curve proves this.

Think of the similar situation where an object is heated. The initial work done raises the temperature of the object, but as soon as it heats up, it starts to cool because heat is radiated and conducted away.

If the object settles at a new higher temperature, energy conservation means the input energy must be equal to the stored energy + lost energy.

So it is with the hysteresis loop. The area bounded by the loop is the lost energy. The upper curve is the extension caused by the input energy and the lower curve is the contraction after energy losses.

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