Rotational equilibrium is a state of a system in which the total angular acceleration is zero. It is when a system has constant rotational velocity and a net torque of zero. In physics, equilibrium refers to a balance of forces, and rotational equilibrium is when all the torques acting on an object are balanced. An object is in rotational equilibrium if its angular velocity is constant, the object is at rest or moving at a constant angular velocity, and the sum of all torques acting on the object is zero. This means that all clockwise and counterclockwise forces are equal. For a system to be at rotational equilibrium, the sum of all torques acting on the system must equal zero. Torque is the rotational equivalent of a force, and it quantifies the turning effect of a force applied to an object. The formula for torque is torque = (moment of inertia) * (angular acceleration) or torque = (force) * (lever arm) .