# Homework Help: Concept Question. Force and Work.

1. Dec 1, 2009

### balletgirl

1. The problem statement, all variables and given/known data

Can the normal force on an object ever do work?

2. Relevant equations

Work= Force x displacement

3. The attempt at a solution

My guess would be no (if there is not any displacement.)

2. Dec 1, 2009

### kuruman

Your guess is correct. If there no displacement there is no work.

3. Dec 1, 2009

### nasu

If by "normal" force is meant normal to the direction of the motion then the work is zero by definition.

However "normal force" can mean the force normal to the contact surface between two objects. When you push an object with another one, the first one is acted upon by the normal force acting between the two objects and it moves along its direction. Work is done in this case. The normal force is not normal to the direction of motion.
The same thing is true for a collision. The interaction forces between the colliding objects have a normal component (may have a tangential component for non centric collision) that does work.

I think is an ambiguous question, out of context. Maybe in the context of the chapter in the textbook with the problem, the meaning was well defined.