I tie a spring to my back and I anchor it to the wall and see how much the spring stretches before the two forces balance.

我把弹簧一端系在背后,另一端固定在墙上,观察两个力平衡时弹簧的伸长量

耶鲁公开课 - 基础物理课程节选

That comes out of postulate three.

即力的平衡。

麻省理工公开课 - 固态化学导论课程节选

That's how by either balancing the unknown force with a known force or by simply measuring the acceleration as I fall towards this podium and multiplying by mass, you can find the force that exerts on me.

我们既可以让未知力与已知力平衡,也可以只测量我冲向讲台时加速度的大小,再与我的质量相乘,都能求出作用在我身上的力的大小

耶鲁公开课 - 基础物理课程节选

That is our force balance.

这就是我们要讲的力的平衡。

麻省理工公开课 - 固态化学导论课程节选