Why is gravity factored at the center of mass in torque problems?

[oneplusone]

Hello,

I was working on a problem dealing with torque, and it was basically a long piece of wood resting on top of two metal poles. (scaffold like), and a worker standing on one end of the wood.

When i was reading the solution, i noticed that gravity was factored in at the center of mass.
I think this is because I chose the pivot point as the intersection of one of the metal poles and the piece of wood.

My question is: is gravity in torque questions ALWAYS factored in at the center of mass??

Thanks a lot!

 

[tiny-tim]

hello oneplusone!

is gravity in torque questions ALWAYS factored in at the center of mass??

yes …

the total gravitational force on a body is always through the centre of gravity (that's for all purposes, not just for torque) …

that's the definition of centre of gravity​

we always assume that any apparatus on Earth is in a uniform gravitational field,

and in a uniform gravitational field, the centre of gravity and the centre of mass are the same (for fairly obvious reasons)