What Is Rotational Equilibrium?

Rotational equilibrium occurs when an object is either not rotating and remains at rest or is rotating at a constant rate – all torques acting on an object have a net value of zero, and there's no rotational acceleration. This occurs due to the rotational analogue to Newton's first law: an object at rest or in motion continues in the same state unless acted on by an unbalanced torque.

In rotational equilibrium, all torques that are acting on an object must be balanced. For example, a torque applied that would spin an object clockwise has to be counteracted by a torque of equal strength that would spin the object counterclockwise. This doesn't necessarily mean all torques acting on the object must be equal to each other, just that each torque needs its equal but opposite force. Although Newton's laws of motion describe the dynamics of linear motion and forces, the same laws govern rotational motion. Torque is the rotational equivalent of force, which causes an object to have rotational acceleration. In addition, torque occurs due to a force applied on a lever arm perpendicular to the axis of rotation. Rotational equilibrium can be seen where there are equal weights on a balanced plane spinning at a fixed speed.