Equilibrium, or BALANCE, is a state of stability in which opposing forces or influences are balanced. It is a concept used in many different fields, such as physics, chemistry, economics, and psychology. In physics, equilibrium is the state in which the sum of all forces acting on a body is zero, and the body is at rest or moving at a constant velocity. In chemistry, equilibrium is the state in which the concentrations of reactants and products remain constant over time. In economics, equilibrium is the state in which supply and demand are equal. In psychology, equilibrium is the state in which an individual's emotions, thoughts, and behaviors are in BALANCE.