It must have momentum, and yet it has no kinetic energy.

它一定有动量，但它却没有动能。

youdao

Kinetic energy and momentum is a totally different thing.

动能和动量，是完全不同的概念。

youdao

So momentum is never exactly conserved, and kinetic energy is never exactly conserved either, so it's only an approximation.

动量并不严格守恒，而动能也从不会，完全守恒，它只是一种近似。

youdao