How to do Equilibrium Problems Involving Possible Rotational Motion

In mechanics, it is important to be able to recognize and solve equilibrium conditions in problems.  In the past, these all involved balancing forces so that objects had no acceleration.  The object was either at rest or moving with constant velocity.

Now that we are doing rotational motion, there is one more possibility.  Not only no linear acceleration, but also no angular acceleration.  For this new condition to be true, there cannot be any net torques on the object.  Remember that torque due to a force = FrsinB, where F is the force, r is the distance from the axis of rotation to the point where the force is applied, and B is the angle between that radius line and line of force.

The conditions we now must consider and set up in problems will be:
           up = down               right = left          and something new:   cw = ccw

This new condition means that any torques trying to make something rotate clockwise (cw) are balanced by torques trying to make the object rotate counterclockwise (ccw).  This video gives an example of how to handle such a system.  Let me know what you think!