Tensors and Relativity: Chapter 2

Relativistic dynamics

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For interacting particles we postulate that


is conserved [ where i labels the particle ] since this is the natural analogue of Newton's law .

Conservation of the time component corresponds to energy conservation  [ with rest mass being included in this ]. Conservation of spatial components corresponds to conservation of three- momentum.

Note that tex2html_wrap_inline1429 is evaluated at a particular time by different observers and they will see different events as simultaneous. However tex2html_wrap_inline1429 will be conserved in all frames.

The center of momentum frame  for a particular system of particles is the one in which