When a body in a selected inertial frame of reference neither rotates nor moves in translational motion, we say the body is in static equilibrium in this frame of reference A body is in equilibrium when it remains either in uniform motion (both translational and rotational) or at rest.

Conditions for equilibrium require that the sum of all external forces acting on the body is zero (first condition of equilibrium), and the sum of all external torques from external forces is zero (second condition of… If one of them is not satisfied, the body is not in equilibrium

equilibrium — body is in equilibrium when its linear and angular accelerations are both zero relative to an inertial frame of reference. static equilibrium — body is in static equilibrium when it is at rest in our selected inertial frame of reference. elastic — object that comes back to its original size and shape when the load is no longer present. free-body diagram for a body — a useful tool that allows us to count correctly all contributions from all external forces and torques acting on the body.