maintaining velocity if it's not acted upon by a force.

速度保持不变的另一种说法
What makes the law surprising is that

这条定律妙就妙在
if I only gave you half the law,

如果只看定律的前半段
namely every body will remain at rest

即如果物体不受外力作用
if it's not acted upon by a force,

将保持静止状态
you will say, "That's fine. I accept that,

你肯定会觉得 "这没什么我能理解
because here's something, you leave it there,

因为你把一个物体放在那里
it doesn't move.

自己肯定不会动
It's not a big surprise."

所以没什么大不了的"
People were used to that from the time of Aristotle.

亚里士多德时代的人们觉得这很自然
But Aristotle used to think that if you want something to move,

但亚里士多德认为如果要让物体运动
there has to be some agency making it move.

那就必须有某种作用让它运动