it has an acceleration towards the center of this size, v^2 over R.

它有一个指向圆心的加速度 v^2 / R
Very simple.

非常简单
It comes from the fact that velocity is a vector

其原理就是速度是矢量
and you can change your velocity vector by changing your direction.

你可以通过改变方向来改变速度
This particle is constantly changing its direction,

这个质点恒定地改变它的运动方向
but it therefore has an acceleration and the acceleration,

因此它具有加速度而且这个加速度
we have shown here, is pointing towards the center.

我们前面也讲过了指向圆心
The size of that is v^2 over R.

它的大小是 v^2 / R
For example, if a car is going on a racetrack

例如如果一辆车在跑道上行驶
and you're seeing it from the top,

你从上面俯视它
if the speedometer says 60 miles per hour,

如果速率表显示的是60英里每小时
you might say it's not accelerating.

你也许会说它没有在加速