# Homework Help: Rotational Motion and Coefficient of Friction

1. Apr 30, 2012

### tajivie

Hey guys!
Ok, so I don't have that much to work with, and I am sorry for my lack of detail, but my memory is a bit fuzzy. I had to do a problem like this for my physics test yesturday:

On the test we were given a problem involving a roller coaster (Rotating Drum of Death was its name). Essentially we were given the radius (for the design of the ride was that of a sphere) and the rotational speed in radians per second. In the problem, the floor of the ride dropped out and but the people on board did not fall to their deaths below because there was a coefficient of friction keeping them inside the ride. The question was to solve for the coefficient of friction. (There was no mass given) Can you please help me solve this problem?

Expereince Info:
This was part of a chapter concerning Rotational Motion. I know how to calculate coefficients of friction when an object is moving down an incline plane, but I have no idea how to solve this problem (also, it was short answer response so there are infinite options)!

2. Apr 30, 2012

### Villyer

Did you draw a force diagram for the person on the ride?

3. May 1, 2012

### tajivie

Yes, I was able to draw a diagram :) My problem though is calculating the coefficient of friction. I believe the radius was 12m and the rotational speed was approx. 8rad/s

4. May 1, 2012

### Staff: Mentor

Hi tajivie! It is customary to post a question only once in the forumhttps://www.physicsforums.com/images/icons/icon4.gif [Broken] I've copied my response in your duplicate thread over to this one. Can you ask for the other one to be deleted?

It has taken me 10 mins of pondering all possibilities before I figured out what this refers to. Misnaming it "rollercoaster" led me way off track to start with.

Okay, you recognize the arrangement they are talking about? So start out with a sketch that helps you determine, for each body, the steady centripetal force pressing it towards the centre of rotation.

Last edited by a moderator: May 6, 2017