it will just slowly go round and round with this tip here.

它就会绕着这个尖端一圈一圈地转
Now, does this remind you of anything you have seen before?

这个有没有让你想起之前遇到的情况呢
Yep.

请讲
The Earth rotating around the Sun.

地球绕着太阳旋转
Right. When we did the Earth rotating around the Sun,

是的当我们讨论地球绕着太阳公转时
or any satellite going around, it was the same thing.

或是卫星绕地球都是同种情况
Here is an apple.

这里有个苹果
If it's not moving, the force of gravity acts on it,

如果它没有运动重力作用于它
causes an acceleration toward the center.

引起一个指向地心的加速度
That means what you and I think it means, falling toward the center.

众所周知这意味着它朝着地心下落
But if you take an apple with a huge velocity to begin with,

如果你在开始给苹果一个很大的速度
add to it an acceleration toward the center,

加上指向地心的加速度