It's very important to notice

需要特别关注的是
that the torque due to this force is the value of the force

力所产生的转矩等于力的大小
times the distance from the point of rotation,

乘以力的作用点到转轴的的距离
and it's only the external force that I'm talking about.

而我所指的仅是外力
There are also internal forces in a rod.

杆的内部也有作用力
Every part of the rod is being dragged along by another part of the rod,

其中每一小段都受到了其它小段的拖拽
but that analysis in terms of forces

这种受力分析
can be done but it's very tricky and complicated.

是可行的但非常复杂困难
It's much easier to look at the energy

从能量的角度分析要简单很多
where the energy changes only due to external forces.

能量的改变量只和外力有关
If you only look at forces you've got to be careful.

如果单纯分析受力你必须很小心
This pivot point is also applying a force on the rod,

这个轴点也对杠杆有作用力