Question

i apply a contact force on a rough horizontal surface and it has constant magnitude . now my question is what happens to the angle between the force and the vertical is decreased when i apply frictional force between the surface and the body

Answer 1

Force of friction is equal to the normal force times a constant of the materials. F = N*u. If you reduce the angle with the surface, you decrease the normal, so you decrease the force. That’s logic because think that when you press with angle, the X component (along the surface) doesn’t approach more the particles between the bodies, but the Y component does, so it makes harder to move along any direction.

Answer 2

good answer

Answer 3

Unless you are pulling rather than pushing, of course, then the normal force gets smaller for a given pull as the angle above horizontal increases by the factor F sin(theta)