And, the way we can get it, so, it's called usually V, so, V here stands for velocity more than for vector. And, you just get it by taking the derivative of a position vector with respect to time.

根据它的原理，我们通常用v表示,这里的V更代表速率而不是矢量，你能通过,对一个关于时间的位置向量求导得到它。

youdao

So to talk about a 3.47 V signal really means nothing unless we know with respect to what reference.

因此我们所说的一个3.47V信号其实并没有什么意义，除非指出其参照物。

youdao

A It tells me that the partial of A with respect to T at constant V is minus S. Right?

他告诉我们,在恒定体积下对温度的微分等于负S，对吗？

麻省理工公开课 - 热力学与动力学课程节选

So, using those, now, what happens if we take the second derivative of A, the mixed derivative, partial with respect to T and the partial with respect to V.

如果我取A的二阶导数,混合导数，对T偏微分,再对V偏微分。

麻省理工公开课 - 热力学与动力学课程节选

And the point is that the second derivative of A, with respect to V and T in this order is the same as the second derivative of a with respect to T and V in this order.

问题的关键在于A的二阶导数，对V和T以这样一个顺序求导,和对T和V以这样一个顺序,求导是一样的。

麻省理工公开课 - 热力学与动力学课程节选