And we have done many problems.

我们也做了很多题目
When a body accelerates there's a reason for it.

物体变速运动是有原因的
Well, all bodies are accelerating towards the Sun.

所有星体的加速度方向都指向太阳
It's fairly clear what the reason is.

原因很清楚
The reason is the Sun.

就是因为太阳
And you then postulate a force that's exerted by the Sun on the planet

假定有一个由太阳施加在行星上的力
that bends it into a circle.

把轨迹弯成了一个圆
And your job is to find out that force.

你们的任务是找到这个力
What's the nature of the force?

这个力的本质是什么呢
So, it is again here that Newton decided

牛顿认为
that the force that bends the planets around the Sun

使得行星绕着太阳转的力
is the same as the force that bends the Moon around the Earth.

和使得月亮绕着地球转的力是一样的