équilibre

Équilibre describes a condition in which opposing forces or influences are balanced, resulting in no net change in the system. The term is applied across disciplines to denote stability, harmony, or a state of rest, though the precise meaning varies with context.

In physics, equilibrium refers to a state in which the net forces acting on an object vanish. Static equilibrium occurs when an object at rest experiences zero net force and moments, while dynamic (or mechanical) equilibrium occurs when an object moves with constant velocity under balanced forces. Equilibria can be stable (small disturbances return to the initial state), unstable, or neutral.

In chemistry, chemical equilibrium arises when the rates of the forward and reverse reactions are equal, so the concentrations of reactants and products remain constant. It is described by an equilibrium constant and can be influenced by temperature, pressure, and concentration, in accordance with Le Chatelier's principle.

In biology and physiology, balance involves the integration of sensory information to maintain posture and spatial orientation. The vestibular system in the inner ear, together with vision and proprioception, supports postural control; homeostatic processes maintain internal stability such as temperature and pH.

In economics and social sciences, equilibrium refers to a state where supply equals demand or where competing interests or forces remain balanced over time. Prices, resource allocations, and social arrangements may shift with external pressures, yet a new equilibrium may emerge.