When is an object considered to be in equilibrium?

An object is considered to be in equilibrium when the sum of all forces acting on it is zero, and the sum of all torques acting on it is also zero. This means that the object is not experiencing any net force, which results in no acceleration, and it is also not rotating, as there is no net torque causing rotation.

In practical terms, when an object is in equilibrium, it will either be at rest or moving at a constant velocity. In the context of mechanics, achieving this state involves balancing all the forces acting on the object, such as gravitational forces, normal forces, friction, and any applied forces, as well as ensuring that any moments (rotational forces) applied to the object also sum to zero.

This understanding of equilibrium is foundational in both static and dynamic situations in physics and engineering, hence why this answer correctly defines when an object is in equilibrium.