这意味着，沿一条闭合曲线，势函数的变化量是。
That means when you go along a closed curve, 0 well, the change of value of a potential should be zero.
如果我们想更加精确一点，我们知道当t变化的时候，乘以导数就出现了，well, t, times, the, derivative, comes, in，这是函数变化量的线性近似。
If we want to be a bit more precise, we know that when we change by t, t that's for linear approximation to how the function changes.
好，既然我们已经知道点的位置，它是一个关于时间的函数，我们就能了解，它在诸如速率或加速度的量中是如何变化的。
OK, so, now that we know the position of the point as a function of time, we can try to study how it varies in particular things like the speed and acceleration.
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