What is the direction of the normal force acting on an object?

Question

1. It is always vertically upwards
2. It can be vertically upwards or downwards
3. It can be vertically upwards or at an angle to the vertical in the upward direction
4. It can never be in the horizontal direction
5. It can be in any direction

Answer 1

(3).

When an object is in contact with a surface the normal force acts perpendicular to the surface and is equal to the component of the object's weight perpendicular to the surface.

So on a flat table (horizontal) normal force is vertical = object's weight (mg).

On an inclined ramp, angle of inclination α, the component of the objects weight perpendicular to the ramp will be mg cos α. This will be the magnitude of the normal force. The direction of the normal force will be α west of the vertical. (if α = 0, ramp is horizontal, normal force is mg, direction is vertical).

Mike

Answer 2

Most students think the normal force is always vertically upwards because they look at an object placed on a flat surface like a table. Some of them realize that this is not always the case. For example, an object placed on an inclined plane has a normal force perpendicular to the plane pointing upwards.

But consider a book at rest being pushed horizontally against a wall. The normal force will act away from the wall in the horizontal direction.

Consider a book being pushed against the ceiling. The normal force will act downwards.

So, the normal force can act in any direction depending on the other forces acting. It always acts in a direction to keep the object at rest.