If the external force on the squash racquet were zero, then it would continue to go always with the same velocity, the center of mass. 若壁球板受外力为,它可能会一直运动,保持同样的速度,而整体的中心。
It could be something like this a squash racquet. 也可能是其他东西,像壁球拍。
And so we have here a squash racquet and we have here the center of mass. 这里有一只壁球拍,这里是质量重心。
So the behavior of the center of mass is extremely predictable, whereas the behavior of the squash racquet is not. 那么整体中心的运动,就是可预测的,而壁球板运动不可知。