Equations of motion when masses move according to Newton's law of gravity. In general relativity, rotational motion is described by the relativistic angular momentum tensor, including the spin tensor, which enter the equations of motion under covariant derivatives with respect to proper time. The Mathisson–Papapetrou–Dixon equations describe the motion of spinning objects moving in a gravitational field. Unlike the equations of motion for describing particle mechanics, which are systems of coupled ordinary differential equations, the analogous equations governing the dynamics of waves and fields are always partial differential equations, since the waves or fields are functions of space and time. For a particular
Speed of gravity radiation field or fluid. Changes in the motion of the attracting body are transmitted by some sort of waves. Therefore, the movements of the celestial bodies should be modified in the order "v/c", where "v" is the relative speed between the bodies and "c" is the speed of gravity. The effect of a finite speed of gravity goes to zero as "c" goes to infinity, but not as 1/"c" as it does in modern theories. This led Laplace to conclude that the speed of gravitational interactions is at least 7×10 times the speed of light. This velocity was used by