Why cant the efficiency of a machine be 100%? We always see that there is some energy that is lost, mostly in the form of heat. But why is it so? Is it impossible to create a machine with 100% efficiency?
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asked Dec 12, 2017 at 16:54
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1$\begingroup$ Friction, mostly, for purely mechanical systems. When dealing with systems that "burn" fuel to create usable energy, though, it kinda gets into thermodynamics. $\endgroup$– Hot LicksCommented Dec 12, 2017 at 18:00
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1$\begingroup$ -1 No research effort. Have you tried googling? $\endgroup$– sammy gerbilCommented Dec 12, 2017 at 19:07
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3$\begingroup$ Possible duplicate of Efficiency larger than one? $\endgroup$– sammy gerbilCommented Dec 12, 2017 at 19:14
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$\begingroup$ See What is the most efficient machine for translating gravitational potential energy of one mass into kinetic energy of a different mass?, and What is the maximum efficiency of a trebuchet? for discussion of efficiency of a purely mechanical machine. $\endgroup$– sammy gerbilCommented Dec 12, 2017 at 19:17
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$\begingroup$ Seems to me that the proposed dupe is asking why $\eta>1$ is not possible while here the question is why $\eta=1$ isn't possible, which isn't really the same thing. $\endgroup$– Kyle KanosCommented Dec 14, 2017 at 12:16
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by machine, i will assume here you mean a physical device with moving parts as opposed to, for instance, a current flowing through a superconducting loop.
the reason no machine with moving parts can be made dissipationless is that it is impossible to make truly frictionless surfaces which can rub or slide or rotate against one another, as well as moving through the air, without dissipating energy.
clever machine design can minimize frictional losses- as in, for example, the guts of a mechanically-driven wristwatch- but even with jeweled bearings, there is always going to be rubbing going on which will turn mechanical work into heat.
answered Dec 12, 2017 at 17:17