The number one feature of a physical book is that it disappears while you are reading it.

一本实体书的最重要的特点是,当你阅读时，它会消失在你眼前。

普林斯顿公开课 - 领导能力简介课程节选

The force may taper off, the force may not be given by a straight line, but for modest deformations, every spring will have a linear regime in which the force is linearly proportional to the stretching.

它产生的力可能会渐渐消失,力的曲线可能不是一条直线,而有轻微的弯曲,每个弹簧都有一个线性区间,在这一区间内,力和伸长量是线性关系

耶鲁公开课 - 基础物理课程节选