But, of course, we want to go all the way to distance, so we take the second derivative and we have this equation for force here.

当然我们最后想要的是距离,所以我们取二阶微,分就有这个式子。

麻省理工公开课 - 化学原理课程节选

This is the pressure that you're applying against the piston, not the pressure of the gas.

最后等于Pext乘以体积,面积乘以距离得到体积。

麻省理工公开课 - 热力学与动力学课程节选