every spring will have a linear regime

每个弹簧都有一个线性区间
in which the force is linearly proportional to the stretching.

在这一区间内力和伸长量是线性关系
It also tells you that if you compress the spring,

它还能告诉你如果压缩弹簧
compress it means x is now--

压缩就意味着现在 x...
x is measured from this position,

x 是从这个位置开始算的
where the spring is neither compressed nor expanded.

在这个位置弹簧既没有压缩也没有伸长
So x is not really the coordinate of the end point.

x 其实并不是弹簧端点的坐标
You've got to understand that.

你们要明白这一点
Springs have a natural length;

弹簧是有原长的
x is measured from that length.

x 就是从这里起算的
If it's positive,

如果它为正值
it means you've stretched it,

就说明弹簧被拉伸了