Second Condition of EquilibriumAn object in equilibrium does not move along a straight line -- it does not

translate-- that means thesum of all the forces on it is zero. That was thefirst condition of equilibrium.But an object in equilibrium also

does not rotate. That means thesum of all the rotational forces on it is also zero.The sum of all the torques on an object is equilibrium is zero. This is theSecond Condition of Equilibrium.Torques that would rotate an object counter clockwise may be taken as positive and torques that would rotate an objectclockwise may be taken as negative. Then we can write this

Second Condition of Equilibriumasor we can calculate the sum of the clockwise torques and set them equal to the sum of the counterclockwise torques. Then we can write this Second Condition of Equilibrium as

Be sure all the torques are calculated about the same origin!

First Condition of EquilibriumTypes of EquilibriumReturn ToC, Rotational Dynamics(c) 2005, Doug Davis; all rights reserved