# Rotational Forces and Torque

1. Nov 8, 2014

### zippeh

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

Let’s have one box, one pulley, and one rolling cylinder. Each of them have mass M, the pulley’s radius is R, and the cylinder’s radius is 2R. Consider the cylinder to be rotating about its center of mass. (a) Draw correct and complete free-body diagrams. (b) Give the equation(s) that come from the free-body diagrams (there are at least 7 equations). (c) Also give the equations that relate the various accelerations to each other (there are at least 4 linear and angular accelerations to consider). You do not need to solve for anything.

2. Relevant equations
Στ=Iα
τ=RFsin(θ)
ΣF=ma

3. The attempt at a solution

I am just confused on the portion of the normal force of the pulley. I included the above photo to demonstrate what I mean. I guess I don't completely understand why the normal force is not parallel to the gravity. It makes sense that it isn't because the T from the cylinder would be equal to 0 (T=Ma -> T=O). I am just confused. Then I guess I am confused on how to compare the accelerations together. Thanks!

2. Nov 9, 2014

### haruspex

For exactly the reason you give. Since the horizontal section of string is tending to push the pulley left, the pulley mounting must resist this by exerting a force to the right.