Question

What is the condition of equilibrium?

Answer 1

The two conditions that are important for equilibrium:

1. The sum or resultant of all external forces acting on the body must be equal to zero.
2. The sum or resultant of all external torques from external forces acting on the object must be zero.

The two conditions given here must be simultaneously satisfied in equilibrium. In essence, for an object to be in equilibrium, it should not experience any acceleration (linear or angular).

So both the net force and the net torque on the object must be zero.