For example, how do I know that when I pull the spring the first time for the mass, it exerted the same force when I pulled the spring the second time for the elephant?

例如 怎样才能知道,第一次连着物体拉弹簧时,产生的力和,第二次连着大象拉弹簧时产生的力是相等的呢

耶鲁公开课 - 基础物理课程节选