3 ms·

Is heat really the end of the line? Heat engine to mechanical, etc.

• TeMPOraL 7y ago
  That's an interesting question. AFAIU, heat engines don't take energy from heat, but from heat difference. In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation, but moving mass between two points of different potential lets you store or extract energy. OTOH, from what little I remember from reaction kinetics in chemistry, temperature there is used as absolute value that determines the chance of collision between their molecules and the "activation energy", both of which influence the rate of a chemical reaction. In this space, thermal energy seems like something absolute. What gives?
  • saagarjha 7y ago
    > In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation Not quite. Potential is defined with an arbitrary basis as you’ve pointed out, but with temperature the basis is not arbitrary: it’s chosen for us, and this value is absolute zero. Taking a temperature difference is not enough to figure out how well a heat engine will work on it.
  • cygx 7y ago
    Note that general relativity requires you to precisely locate all (non-gravitational) energy contributions as they determine spacetime curvature. So while eg the electrostatic potential has an arbitrary zero point, the energy density of the electromagnetic field has not. The only exception to that is gravitational energy, which cannot entirely be localized.