Conditions for equilibrium

If the net torque acting on a rigid body is zero, the body will not rotate or continue to rotate with constant angular frequency. If the net force acting on the object is zero, it will stay at rest or continue to move with constant velocity. If both conditions are met, the object will be in equilibrium.

Being in equilibrium means the state of motion of the object (involving translational and rotational motion) does not change.

Conditions for equilibrium

An object will be in equilibrium if both of the following conditions are met:

the net external force is zero,

\[\sum\mathbf{F} = 0,\]

and the net external torque about any axis is also zero,

\[\sum\mathbf{τ} = 0.\]