...型 刚体中所有质点的相对位置均固定不变 二、刚体的运动 刚体上所有点的运动都相同 (1)定轴转动（rotation around a fixed axis） (2)定点转动（rotation around a fixed point） 3、一般运动 总可以看成平动与转动的叠加 刚体的自由度（Degree of Freedom）...
abstract:Rotation around a fixed axis is a special case of rotational motion. The fixed axis hypothesis excludes the possibility of a moving axis, and cannot describe such phenomena as wobbling or precession.
Of course, with the camerafixed to atripod, the stars themselves produce concentrictrails in longexposures, a reflection of the Earth'srotation around its axis.