Equilibrium is the condition when the motion of a body does not change with time. It can be categorized as static or dynamic equilibrium. In static equilibrium, the object is at rest. Whereas, if it is moving with constant velocity, the object is said to be in dynamic equilibrium. For a system to be in static equilibrium, it should satisfy two conditions simultaneously. First, its translational velocity should be zero, for which there should be no net external force acting on the body. Second, its rotational velocity must be zero. This is satisfied when net torque due to all the external forces acting on it is zero. Consider a freely-moving weighing balance having equal masses on each side. A static equilibrium is established when the net force and the net torque acting on the system are balanced.