Energy related problem

[rktpro]

When we fail to move a heavy stone even after applying force, is work being done in this case? Is energy transformation taking place

Edited November 27, 2010 by swansont
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[lemur]

You have to trace the utilization of energy through the entire system you're concerned with. If you're using your muscles to apply force to the rock, then work is being done to contract the muscles. When the rock fails to budge, however, the energy you exert is being used to maintain muscle-contraction. If your muscles lose energy, they will stretch to their maximum length and you will no longer be exerting force against the rock. Technically, you're also compressing and shifting the rock in a way that is getting it closer to moving, although the shift is not noticeable. If you impart enough energy into the rock to move it, it will have basically acted like a spring storing up that energy until the threshold of movement was reached.

[swansont]

No work is done on the rock. Energy has been expended, though, and the simplest treatment of this is probably thermodynamics: you have converted some energy into 0% work and 100% waste heat.

[rktpro]

You have to trace the utilization of energy through the entire system you're concerned with. If you're using your muscles to apply force to the rock, then work is being done to contract the muscles. When the rock fails to budge, however, the energy you exert is being used to maintain muscle-contraction. If your muscles lose energy, they will stretch to their maximum length and you will no longer be exerting force against the rock. Technically, you're also compressing and shifting the rock in a way that is getting it closer to moving, although the shift is not noticeable. If you impart enough energy into the rock to move it, it will have basically acted like a spring storing up that energy until the threshold of movement was reached.

 

Is work done when you contract your muscles. I think NO

[lemur]

Is work done when you contract your muscles. I think NO

 

The muscle cells move when they contract and that motion entails work. You are right, though, that if you just count your overall position not moving due to muscle contraction, then no work is being done in that frame. Nevertheless it is not true that no work is being done at any level.