Based on the theorem for the compositionofvelocities in theoretical mechanics, the author gives out the demonstration of the theorem of three instantaneous centers of velocity in general conditions.
本文运用理论力学中运动学的速度合成定理，给出了一般情况下平面机构运动三心定理的求证过程。
2
Expressions ofvelocities and accelerations in usual coordinates are simply derived by means of the composition formulae of velocity and acceleration in special rotation reference systems.