费恩曼物理学讲义中的问题.

题目

费恩曼物理学讲义中的问题.
我用中文说可能翻译的不太确切,直接上原文了.Now let us put twice as many molecules in this tank,so as to double the density,and let them have the same speed,i.e.,the same temperature.Then,to a close approximation,the number of collisions will be doubled,and since each will be just as"energetic"as before,the pressure is proportional to the density.If we consider the true nature of the forces between the atoms,we would exoect a slight decrease in pressure because of the attraction between the atoms,and a slight increase because of the finite volume,they occupy.如何解释文中的因为原子之间的吸引力而导致压强轻微减小?

答案

因为压强就是原子撞击容器壁的动量的改变,考虑吸引力后,这些吸引力提供了一部分指向内部的冲量,从而减少了容器壁需要的冲量,也就是压强有轻微的减少