* Mechanical Equilibrium: This means the object is at rest or moving with a constant velocity.

* Newton's First Law: This law states that an object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

* Acceleration: Acceleration is the rate of change of velocity. If the velocity is constant (or zero), then the acceleration is also zero.

In simpler terms: If an object is in mechanical equilibrium, it's not speeding up or slowing down, and it's not changing direction. This means its acceleration is zero.