First, we got to make sure the spring exerts a fixed force every time.

首先,要保证,弹簧每次产生的力是恒定的

耶鲁公开课 - 基础物理课程节选

We don't know what the force of the spring is.

我们不知道弹簧的力多大

耶鲁公开课 - 基础物理课程节选

We did the comparison with the elephant or something; a is the second derivative of x and for this problem, when F is due to a spring, we know the force is that by studying the spring.

我们也已经把它与大象或其它东西作过比较,a 是 x 的二阶导数,在这个问题中,F 是由弹簧产生的,我们在讨论弹簧问题时已经知道了力的大小

耶鲁公开课 - 基础物理课程节选