A body R, regardless of shape and volume, with the characteristic that the relative distance between any two points of R remains constant, even if the body is acted upon by external forces. Since all real materials deform at least slightly, rigid bodies do not exist in the real world. However, in cases where a body's deformations are small and therefore unimportant for defining its mechanical status, it can be useful to approximate the body as rigid.
Deformable Body, Euler's Equations of Motion
