Abstract
In relativistic mechanics the forces acting on a body have the following two properties: (i) their sum is equal to the rate of change of momentum of the body, and (ii) they have certain prescribed transformation properties under Lorentz transformations. It is pointed out that not both of these properties can be taken over to relativistic thermodynamics: they lead to different interpretations of the energy-momentum tensor and its divergence for a heat conducting continuum. Postulating the first of them gives the thermostatics of Planck and others, whereas postulating the second one gives that of Ott, Kibble, Møller, and others. The work differential of Kibble and Møller is generalized to include changes of velocity. The equilibrium of rotating systems is also discussed.
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