If an object is at rest and is in a state of equilibrium, then we would say that the object is at 'static equilibrium.' 'Static' means stationary or at rest. This too extends from Newton's first law of motion. in motion and continuing in motion with the same speed and direction.But having an acceleration of 0 m/s/s does not mean the object is at rest. This extends from Newton's first law of motion. Objects at equilibrium must have an acceleration of 0 m/s/s. Thus, the net force is zero and the acceleration is 0 m/s/s. Balanced is the key word that is used to describe equilibrium situations. If an object is at equilibrium, then the forces are balanced. The 50 N force is not equal to the 30 N force. Note that the two objects are at equilibrium because the forces that act upon them are balanced however, the individual forces are not equal to each other.

Consider the two objects pictured in the force diagram shown below. This however does not necessarily mean that all the forces are equal to each other. The forces are considered to be balanced if the rightward forces are balanced by the leftward forces and the upward forces are balanced by the downward forces. When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium.

3d equilibrium statics problems