851 Motion of a Rigid body 刚体的平动、转动和定轴转动 1. The model of a rigid body刚体模型 Rigid body(刚体): an ideal mode The distance between two points in a rigid body maintains constant forever. Thus the body has a perfectly definite unchanged shape and size. 刚体是一种理想模型:刚体是在任何外力作用下任意两点间 均不发生位移,形状大小均不发生改变的物体1. The model of a rigid body 刚体模型 Rigid body（刚体） : an ideal model 刚体是一种理想模型：刚体是在任何外力作用下任意两点间 均不发生位移，形状大小均不发生改变的物体。 §51 Motion of a Rigid Body 刚体的平动、转动和定轴转动 The distance between two points in a rigid body maintains constant forever. Thus the body has a perfectly definite, unchanged shape and size