# Homework Help: Rotational motion with inertial forces

1. Sep 8, 2016

### OnAHyperbola

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

2. Relevant equations

Centripetal acceleration$$=\omega ^2R$$
Coriolis acceleration $$=2v_{rot}\omega$$
3. The attempt at a solution

Think of the mass as lying on an incline. The forces I know are parallel to the incline are $$mgsin(\alpha), \mu N$$
Forces I know are perpendicular to the incline are $$mgcos(\alpha),N$$. What I'm unsure about is how to deal with centripetal and coriolis forces. Could someone shed some light on this?

Last edited by a moderator: Sep 8, 2016
2. Sep 8, 2016

### BvU

Hi,
Does the block move in the rotating frame of reference ? So what about the Coriolis force ?

3. Sep 8, 2016

### OnAHyperbola

As seen by an observer relative to whom the cylinder is rotating, the block is stationary. That must mean that it is moving in the rotating frame of reference. So there must be a Coriolis force on the block, right? I don't think there is any centripetal force on the block in the rotating frame.

4. Sep 8, 2016

### BvU

The exercise wants you t find $\omega$s for the case the block does not slip !

5. Sep 8, 2016

### OnAHyperbola

Yes, does not slip relative to a stationary observer who sees the cylinder as rotating. I can see that.

6. Sep 8, 2016

### BvU

More imporantly: "stays still wrt the rotating cylinder" !

7. Sep 8, 2016

### OnAHyperbola

Oh..so it is rotating... No coriolis force in that case, just centripetal and centrifugal (in the block's frame) then?

8. Sep 8, 2016

### BvU

Yes. Some gravity and some friction too