Rotational Motion and Equilibrium

A rigid body is an object or a system of particles in which the distances between particles are fixed. In pure rotational motion, all the particles of an object have the same instantaneous angular velocity. As with translational motion, a force is necessary to produce a change in rotational motion. Rotational acceleration is not always produced when a force acts on a stationary rigid body. Torque in rotational motion can be thought of as the analogue of force in translational motion. Unbalanced forces produce translational accelerations, but balanced forces produce the condition called translational equilibrium. The rotational “directions” are taken as clockwise or counterclockwise around the axis of rotation. Torque is the rotational analogue of force in linear motion, and a net torque produces rotational acceleration. A rigid body in mechanical equilibrium may be either at rest or moving with a constant linear and/or angular velocity.