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Equilibrium

ee-kwih-LIB-ree-um /ˌiːkwɪˈlɪbriəm/

nounC1GRESAT

FormalScientific

A state in which opposing forces or influences are balanced, resulting in no net change or motion.

In physics, equilibrium means the net force and net torque on an object are zero. This can mean the object is at rest (static equilibrium) or moving at a constant velocity (dynamic equilibrium).

The story behind the word. "Equilibrium" comes from the Latin "aequilibrium," meaning "an even balance." It combines "aequus" (equal) and "libra" (a balance, pair of scales). Thus, the word literally means "equal balance," perfectly describing a state where all forces are evenly matched.

Word relationships

balance: "Balance" is a general term for stability; "equilibrium" is the precise scientific term for a state of no net force/change.
stability: "Stability" implies resistance to disturbance, which is often a characteristic of a system in equilibrium.

imbalance: A state where forces are not equal or balanced.
disequilibrium: A lack of balance or stability.

Commonly confused with

Stasis: Stasis implies a complete halt or inactivity; equilibrium can involve constant motion (dynamic equilibrium).

Word family

equilibrate (verb): To bring into equilibrium.
equilibrant (noun): A force that produces equilibrium.

Collocations

static equilibrium
dynamic equilibrium
thermal equilibrium
chemical equilibrium
restore equilibrium

Idioms & expressions

upset the equilibrium

Example sentences

"The carefully constructed arch remained in perfect equilibrium, distributing its weight evenly." Describing a stable structure.
"In a perfectly competitive market, supply and demand will eventually reach a state of equilibrium." From an economic principle. (Principles of Economics)

Memory hook

EQUILIBRIUM means everything is EQUAL and balanced, like a LIBRA (scales). Equal Balance

When not to use

While "equilibrium" can be used metaphorically (e.g., "emotional equilibrium"), ensure the context is clear if you mean the physical state of balance.

Fun facts

A tightrope walker maintains dynamic equilibrium by constantly adjusting their center of mass.
The concept of equilibrium is vital in engineering, chemistry, and economics.