# Equal and Opposite Forces

I was wondering how Newton's Third Law is related to contact and normal forces. What about at an angle? The normal force is equal only to perpendicular force exerted downwards, perpendicular to the angle but does the addition of the perpen. force and the the parallel force to the angle equal weight? So does the law still fundamentally apply? But they are not exactly the same thing...?

Also, on forces that act at a distance, like gravitational forces, what is the reaction force? When the earth pulls on you, calculated by f grav = m * g, does the earth feel the same force towards you?

A.T.
does the addition of the perpen. force and the the parallel force to the angle equal weight?
Yes.

D H
Staff Emeritus
Also, on forces that act at a distance, like gravitational forces, what is the reaction force? When the earth pulls on you, calculated by f grav = m * g, does the earth feel the same force towards you?
Yes.

does the addition of the perpen. force and the the parallel force to the angle equal weight?
If you tautologically define weight as the sum of the perpendicular and parallel forces (normal force and friction), the answer is "yes".