Then the second derivative gives the change in entropy with respect to the variable that we're differentiating, with respect to which is either pressure or volume.

二阶导数给出熵,随着变量变化的情况，这些变量包括压强或者体积。

麻省理工公开课 - 热力学与动力学课程节选

And the useful outcome of all that is that p we get to see how entropy changes with one of those variables in terms of only V, T, and p, which come out of some equation of state.

这样做的重要结果是,我们得到了熵随着V，T或者,其中一个变量变化的情况，这些可以从状态方程得到。

麻省理工公开课 - 热力学与动力学课程节选