# Homework Help: Question on circular motion and newton's laws

1. Oct 29, 2007

### excel000

1. What are the action/reaction forces when twirling a rubber stopper attached to a string? How does circular motion illustrate newton's first law?

2. F=ma

3. I thought about centripetal and centrifugal, but my teacher said centrifugal force isnt a real force.

2. Oct 29, 2007

### PhanthomJay

Your teacher of course is correct. When you talk of 'action/reaction' forces, you're talking usually about Newton's 3rd Law 'force pairs', whereby if A exerts a force on B, then B exerts a force on A that is equal in magnitude but opposite in direction to it. Does that help?

3. Oct 29, 2007

### excel000

yea, but i can only think of the tension force, i cant think of the opposite to that. how about the force applied by the hand and the tension force?

4. Oct 29, 2007

### PhanthomJay

Yes, that's one of them. If the hand pulls on the string creating a force in the string, then what can you say about the force of the string on the hand? What about the stopper/string force pair?