Suppose the particle is not moving in a circle, but does this.

假设这个质点不是做圆周运动,而是这样

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Whenever you see a particle moving in a circle, even if it's at a constant speed, it has an acceleration, v square over r directed towards the center.

只要看到质点做圆周运动,即使是匀速圆周运动,也存在一个加速度,大小为 v^2 / r,方向指向圆心

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In other words, you don't have to be moving actually in a circle to have the acceleration.

也就是说,你不必真的在一个圆上运动以获得相应的加速度

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