# Normal Force during centripetal acceleration

1. Oct 7, 2012

### prospectus

General Question Here:

Let's say you are swinging a ball around on a string. Will there be a normal force?

2. Oct 7, 2012

### AJKing

That's a good question and it depends on your perspective.

If you take the view point of an outside observer, then no. There is the tension in the string, the circular speed and the radial acceleration; all motion is accounted for from that perspective.

If your view point is from the ball, then yes. There is a pseudoforce acting on you that pulls you away from the center. That pseudoforce is the normal force, which is opposite from the acceleration.

It's not a topic that I have much depth on, but that is what I know.

Research non-inertial reference frames for more.

3. Oct 8, 2012

### prospectus

Thank you. It makes sense that there would be no normal force because there is no surface acting on the ball.

4. Oct 8, 2012

### AJKing

You're welcome.

I'd just like to append what I said with this:
What I described from the view point of the ball would not be a normal force either. That is still a pseudoforce.
A normal force always requires contact with a surface.

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