How Does Vertical Force Affect Normal Force on a Block?

[sweet-buds]

Homework Statement

A vertical force F is applied to a block of mass m that lies on a floor. what happens to the magnitude of the normal force N on the block from the floor as magnitude F is increased from zero if force F is a)downward b)upward

Homework Equations

Let m be the mass of body. ideally if the body were to be at rest , and considering only vertical motion, N(reaction force on body from surface)=mg
1) if force F is downward, F+mg> N. The N would adjust in a way such by increasing it s value so that it can counter F+mg force else the block will break through the surface

2)the N would decrease or else the block would raise above the surface.

The Attempt at a Solution

a)downward= N increases
b)upward=N decreases

 

[Mindscrape]

Yes, you are correct. Intuition plays a good role in this case too because if you push down on a block harder, then the floor is going to have to push back harder for the forces to cancel and the block to stay still.

 

[Dick]

Yes, absolutely. But don't even worry about the case where the block has a velocity in the vertical direction. That's not a situation where you would even think much about static normal forces.