这些营力过程大致可分为三类：内营力过程、外营力过程和人类活动过程。

These forces processes can be divided into three kinds of processes, endogenic forces process, exogenic forces process and human activity process.

在强制对流中，液体或气体的运动是产生压力差的某种外营力造成的。

In forced convection the movement of the fluid or gas is caused by an external agent which gives rise to pressure differences.