The weight of a body acts through the center of mass of the body. If every particle of the body is attracted by earth, then why do we assume that the weight acts through the center of mass? I know that this is true but I can't understand it. Does it mean that the earth does not attract other the other particles of the body ? Wouldn't it mean that girders would not need any support at the periphery if we erect a pillar at the center?
[Physics] Why do we assume weight acts through the center of mass
newtonian-gravitynewtonian-mechanicsreference framesrotational-dynamics
Best Answer
The other answers here, which show that gravity does not exert a torque on an object, are correct. However, they rely on the following implicit step of logic to get to the answer the OP wants:
An object that has a force acting on it, but no torque acting on it appears as if it is being pulled from its center of mass.
This is true in the case of ideal rigid bodies only. In the case of elastic objects, OP is absolutely correct, in that gravity does indeed act on each individual particle in the object. This is why girders bend under their own weight, among other things.