How to Calculate the Minimum Couple to Rotate a Cylinder on Inclined Planes

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Homework Help Overview

The problem involves a uniform cylinder resting in equilibrium between two inclined rough planes, with the goal of determining the minimum couple required to initiate its rotation. The scenario includes specific parameters such as the angle of inclination and the coefficient of friction.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the importance of constructing diagrams to visualize forces acting on the cylinder, including normal reactions and friction forces. There is uncertainty regarding the correct axis of the cylinder and how to represent it in the diagrams.

Discussion Status

Some participants have provided guidance on the necessity of diagrams and the resolution of forces, while others express confusion about the cylinder's axis and how to approach the drawing. Multiple interpretations of the problem setup are being explored.

Contextual Notes

Participants are grappling with the specifics of the cylinder's axis and the implications of the inclined planes, which may affect their understanding of the problem. There is an emphasis on visual representation as a key component of problem-solving in this context.

Johnny87
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A uniform cylinder of radius a and weight W rests in equilibrium between 2 rough planes which are both inclined to an angle pi/6 to the horizontal. The axis of the cylinder is parallel to the line joining the two planes and the coefficient of friction at both points of contact is 1/2.

Find the least couple which must be applied to the cylinder to make it rotate.




Please help me! Who knows how this can be done?
 
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Construct a diagram of the forces before the cylinder rotates. Resolve forces and find the normal reactions.

The draw the diagram again for the block in rotation...you know the weight and normal forces, so you can find out the Friction forces and hence the couple...

Diagrams are the answer.
 
The problem is I don't know how to draw the diagram.. For example, which axis of the cylinder is it talking about? (Cylinders have more than one axis, if I'm correct)
I'm really confused.
 
Cilinders have only one important axis. The other two are of no importance.
 
Which is..?
 
The one that determines the rotational vector of a 'common' rotating cilinder wheel.

You know, the one that goes through he center of the cilinder?
 
Last edited:
always go for the simplet solution - imagine a vee shape. in the vee is a circle. this is an end on view
 

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