# Difference between circular motion and rotational motion

1. Dec 6, 2015

### Mr Davis 97

I don't really understand the difference between uniform circular motion and rotational motion. I know that uniform circular motion deals with a body that is orbiting around a central point, with a centripetal force that is causing it to move in a circle. I know that rotational motion uses angles to describe how a body rotates around a central axis. However, aren't these basically equivalent? Each one involves a point revolving around a central axis. Is the real difference that rotation is described in terms of angles, and uniform circular motion is described in terms of linear acceleration and velocities?

2. Dec 6, 2015

### Student100

Basically.

Uniform circular motion describes transitional movement around a fixed point, while angular motion describes how a body rotates about an axis. In strictly angular motion, the bodies center of mass doesn't undergo any translation movement.

You can have a body that undergoes angular motion while the center of mass undergoes a linear translation movement. (Move's in a straight line) You can also have a body that undergoes both uniform circular motion and angular motion.

3. Dec 6, 2015

### Mr Davis 97

Okay, that makes sense. I have another question. If we have a steel ball, and it is rotating about an arbitrary axis and is not in transnational motion, is there a centripetal force acting on every particle of the ball?

4. Dec 6, 2015

### nasu

Yes, there is. The centripetal force is "provided" the inter molecular forces that keep the particles together in the steel ball.

And by the way, both types of motions mentioned in the OP can be described by angular quantities. And both can be described in terms of linear quantities as well.
For the spinning of extended objects, the linear quantities may not be so convenient but they are there.

5. Dec 6, 2015

### Mr Davis 97

So the choice between tackling a problem in terms of angular quantities or linear quantities is determined by the information provided and which one would be easier to use in a specific case?

6. Dec 6, 2015

### rootone

You might find it interesting to look in to how jet engines work.
Turbofans are even more interesting.

7. Dec 6, 2015

### nasu

Yes. Or you can use both even in the same problem.
In general the motion is a combination of translation and rotation, anyway.