Mechanical equilibrium occurs when an object is at rest or moving at a constant velocity, meaning the net force acting on it is zero. In this state, all the forces acting on the object balance each other out, resulting in no acceleration. This principle is essential in understanding how structures like bridges and buildings maintain stability. There are two types of mechanical equilibrium: static and dynamic. Static equilibrium refers to objects at rest, while dynamic equilibrium involves objects moving at a constant speed in a straight line. Both types are governed by Newton's laws of motion, which describe the relationship between forces and motion.