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Equilibrium

ee-kwih-LIB-ree-um /ˌiːkwɪˈlɪbriəm/

nounC1GRESAT

formaltechnicalgeneral

A state in which opposing forces or influences are balanced, resulting in a stable system.

In physics, equilibrium can be static (at rest) or dynamic (in constant motion, but with no net change). It implies a balance of forces and/or torques. In chemistry, it refers to a state where forward and reverse reaction rates are equal.

The story behind the word. The word 'Equilibrium' is a beautiful combination of Latin roots: 'aequus', meaning 'equal', and 'libra', meaning 'balance' or 'scales'. So, 'equilibrium' literally means 'equal balance'. This term has been used since the 17th century to describe a state where all forces are perfectly matched, leading to a stable and unchanging condition.

Word relationships

balance: Often interchangeable, but 'equilibrium' can imply a more precise or dynamic balance of forces.
stability: Stability is the quality of being resistant to change; equilibrium is the state where forces are balanced, leading to stability.

imbalance: A lack of balance or proportion.
instability: The state of being prone to change or collapse.

Commonly confused with

Stability: Equilibrium is the state of balanced forces; stability is the resistance to disturbance from that state.

Word family

equilibrate (verb): to bring to a state of equilibrium

Collocations

thermal equilibrium
chemical equilibrium
dynamic equilibrium
restore equilibrium
lose equilibrium

Idioms & expressions

strike an equilibrium

Example sentences

"A tightrope walker maintains their equilibrium by constantly adjusting their center of gravity." Describing a physical state.
"For a bridge to stand strong, all the forces acting upon it must be in a state of equilibrium." In a mechanical system.
"When a chemical reaction reaches equilibrium, the concentrations of reactants and products no longer change." In a chemical context.

Memory hook

Think of 'EQUI' (equal) and 'LIBRA' (like the scales of justice, representing balance). Equal balance. Perfect balance

When not to use

While 'equilibrium' can be used metaphorically for mental or emotional balance, be precise in scientific contexts to refer to a physical or chemical state of balance.

Fun facts

The concept of equilibrium is fundamental to statics, a branch of mechanics that deals with forces in systems at rest.
In economics, market equilibrium refers to a state where supply equals demand.