# Mechanics, Torgue

1. Feb 28, 2009

### Kurret

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

A cylinder of mass M and radius R is rotated in a uniform V groove with constant angular velocity w. ( the V groove is symmetric with a 90 degrees V, and 45 degrees on both sides of the V to the horizontal plane). The coeff. of friction between the cylinder and each surface is f. What torque must be applied to keep it rotating?

2. Relevant equations
t=fxR

3. The attempt at a solution
The keep it rotating with constant angular velocity, the net torque must be zero. The torque from the friction for each side of the V is R*f*Mg/Sqrt(2), so the total torque should be Sqrt(2)*RfMG. Thus we must apply the same torque to keep it rotating.

Now this seemed too good to be true, and it certainly was. The answer should also be divided by (1+f^2). Why???

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2. Feb 28, 2009

### tiny-tim

Hi Kurret!

Call the two normal forces N and M, draw in the friction forces, and take componenets both horizontally and vertically to find N and M.

3. Feb 28, 2009

### Kurret

Thanks Tim! :)

4. Feb 28, 2009

### Kurret

But, when we apply the torque, will not the force from the torque we apply also affect the normal forces???

5. Feb 28, 2009

### davieddy

No. Assume that the torque is applied by a "couple".