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This question already has an answer here:

If I put a brick onto an steel platform, that platform can hold the brick A LONG TIME, if not FOREVER. Does the platform exert force? If so, then shouldn't it have infinite energy to resist the pull of gravity? If not, shouldn't it hold at least an ENORMOUS amount of energy to support the brick? And if the platform does NOT exert energy, then what is holding the brick back from plummeting to the earth?

Thanks guys! :)

EDIT: Come to think of it, the platform is held together by the electromagnetic force. But I still wonder whether or not gravity and the other fundamental forces have infinite energy or not.

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marked as duplicate by ACuriousMind, Kyle Oman, John Rennie, Ryan Unger, Kyle Kanos Apr 23 '15 at 1:34

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Energy is only expended in movement. In a stationary configuration (holding a brick), energy is not expended. The brick is held back by a static force, which requires no input to maintain itself and expends no resources in doing so.

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  • $\begingroup$ So... a force that requires no energy yet resists energy inputted against it? @zeldredge $\endgroup$ – HyperLuminal Apr 22 '15 at 17:47
  • $\begingroup$ There is no energy input against it. Work is only done by a force if the object the force is on moves. A stationary object, even when subjected to forces, has no work done on it. Its energy does not change. Therefore no energy is spent by the external force. $\endgroup$ – zeldredge Apr 22 '15 at 17:49
  • $\begingroup$ How about gravity? It moves objects. Does it expend energy? @zeldredge $\endgroup$ – HyperLuminal Apr 22 '15 at 17:56
  • $\begingroup$ Yes. When it moves objects. When an object is sitting at rest on a shelf, it does not expend energy. When two objects move towards each other, the gravitation potential energy in the system composed of those objects is reduced. $\endgroup$ – zeldredge Apr 22 '15 at 17:57

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