Somehow, if you could manufacture a really smooth frictionless surface,

如果你制造一个绝对光滑无摩擦的表面
that if you took a hockey puck or something

然后在上面放个冰球或者别的什么
and an air cushion and you give it a push,

或者气垫然后推它一下
in some idealized world,

在理想条件下
it'll travel forever.

它会永远运动下去
So it's hard to realize that in the terrestrial situation.

这在现实世界很难实现
But Galileo already managed to find examples

但伽利略已经成功找到了
where things would roll on for a very, very long time.

物体可以运动很长很长时间的例子
Nowadays, if you go to outer space,

现如今如果你去了外太空
you can check for yourself that if you throw something out,

你可以向外抛个物体试试
it just goes on forever without your intervention.

如果你不打断它它就会一直运动下去
It's in the nature of things to go at a constant velocity.

能保持恒定速度是物体的固有性质