Max von Laue,
Remarks on the Law of the Lever in the Theory of Relativity
“ Certainly, it is by far outweighed by the convection current of the energy-forms that are resting in matter, so that the parallelism of momentum density and velocity can remain as an approximation, which is quite sufficient in most cases. ”
Max von Laue,
Remarks on the Law of the Lever in the Theory of Relativity
“ According to (5) , the momentum density is always parallel to the velocity. However, nothing similar is valid with respect to the energy current . For example, think about a transmission belt; here, the energy current conveyed by its stress arises opposite to the velocity; or think about a rotating drive shaft; it conveys (by its torsion) an energy transport perpendicular to the velocity of the material parts. In general, the conduction current of the mechanical energy caused by the elastic stresses, can in general have any direction with respect to the velocity. ”
Max von Laue,
Remarks on the Law of the Lever in the Theory of Relativity
“ As I have shown at another place [4] , this is only the case for bodies which are unaffected by external forces, and which are in static equilibrium in their rest system. For such ones, the dynamics of the mass point (as it was developed by Einstein and Planck) is valid, and this is completely independent from other properties of their constitution. ”
