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Q & A: Is an electric heater a machine?

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Most recent answer: 01/22/2015
Q:
Is an electric heater a machine? Does a machine have to have moving parts? Would a 100% efficient machine be perpetual motion? Does work happen only when the forces generated or redirected cause movement?
- Dwight H Simmons (age 63)
NYC NYC
A:

The electric heater question is basically about words. You can pick any definition of "machine" that's convenient.

I guess by the usual definitions a 100% efficient machine would be one that kept all its energy in some mechanical form, not losing any to little random thermal (entropic) modes. Such machines don't exist. If you wanted to call an electric heater a machine, it would be ~0% "efficient" (on purpose) by this definition.

There are various forms of work, direct transfer of mechanical energy from one form to another. That most familiar ones from beginning physics classes involve movement. That makes sense because kinetic energies are energies of motion, and familiar potential energies are energies due to relative positions, which change via movement. There's also potential energy from interaction between the spins of particles like electrons and other spins and magnetic fields. So changing a magnetic field can do work on some spins even if they don't go anywhere.

 Mike W.


(published on 01/22/2015)

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