# Torque required to rotate a circular sector inside a drum

1. Mar 1, 2013

### subbby

What I have ?
• Have a 16’ x 72’ rotating drum
• There is a solid circular sector inside the drum

What I need ?
Want to Calculate the torque required to move that solid circular sector from the intial position to the position shown in attached picture (90 Degrees rotation)

Data :
• RPM = 10
• time = 15 seconds

What I have caluted ?
• Calculated the torque required to rotate the drum using Torque = Moment of Inertia X Alpha where Alpha = angular acceleration

How do I proceed ?
1. Do I have to calculate the moment of inertia of that solid circular sector and then use the same formula?
2. But here its not a complete rotation. Its just 90 degrees. So how to arrive at torque to move a mass about an axis only to a certain degree?
3. Or, Should it be just Torque = Force * Radius ? where force shall be its mass * acceleration due to gravity and radius shall be distance from the drum's rotation axis to the circular sector's center of gravity ?
4. Does Perpendicular axes theorem or Parallel Axes theorem come into the picture ?

File size:
18.5 KB
Views:
450
2. Mar 1, 2013

### rock.freak667

You will need to get the total moment of inertia of the drum + circular section. For that you may need the parallel axis theorem.

As for the rotation of the 90 degrees. What is the definition of angular acceleration?

3. Mar 4, 2013

### subbby

I am afraid , I didn't understand. My approach was to find the Inertia of both separately and then arrive at their individual torques. Did you mean the same ? Do we need a parallel axis theorem in that ? If yes, could you explain a little more elaborately ?

Angle was taken to be ∏/2.
Therefore, Angular Velocity = (∏/2)*rpm/60 = (∏/2)*10/60=.26 s^(-1)
and Angular acceleration = .26/time = .26/15 =0.0174 s^(-2)