Equilibrium describes a state or process in that is in balance. When dealing with two or more opposing forces, a state of equilibrium specifies that the opposing forces balance. With regard to mechanics, at equilibrium there is zero net force on a body (i.e., the body must have constant velocity). In chemistry, equilibrium specifies a state where processes occur at equal rates, and result in zero net change in reactants and products. Static, rotational, and translational equilibrium all refer to the motion of objects. Thermal equilibrium is used when referring to temperature. Physical equilibrium deals with changes between gas, liquid, and solid states.

Static equilibrium is a state in which all the forces acting on an object are balanced so that the body experiences constant velocity (including, with regard to an appropriate reference frame, a state of rest). There are two physical conditions that must be met...