equilibrium
Pluralequilibriums, equilibria
- 1The state of a system in which opposing influences balance one another, so that there is no overall change.
Wolves and deer in the valley eventually reached a natural equilibrium that held for decades.
Any new tax upsets the market's equilibrium, at least for a while.
Oppositeimbalance, instability, disequilibrium
Note
The word pictures a pair of scales hanging level: Latin aequilībrium joins the root for “equal” with lībra, “balance”. It has two plurals, and both are in use: equilibriums, and the Latin equilibria that Philip Miller's The Gardeners Dictionary applies to liquors.
- 2Mental balance; a steady, composed state of mind.
It took her a week of quiet to recover her equilibrium after the funeral.
One rude email can wreck my equilibrium for the whole morning.
Similarsanity
Oppositeinstability
- 3In physics, the state of a body at rest or moving uniformly, in which all the forces acting on it add up to zero.
A bridge is designed so that every joint stays in equilibrium under its expected load.
A car cruising at constant speed on a level road is in equilibrium, since the engine's push exactly matches drag and friction.
Similarbalance
Oppositedisequilibrium
Note
Physicists tell three kinds apart by what a small nudge does. In stable equilibrium the body comes back, like a ball at the bottom of a bowl; in unstable equilibrium it runs away, like a ball balanced on a hilltop; in neutral equilibrium it stays where it was pushed, like a ball on a level floor.
- 4In chemistry, the state of a reversible reaction in which the forward and reverse reactions proceed at the same rate.
At equilibrium, ammonia is formed and broken down at exactly the same rate.
Chemists raise the pressure to shift the equilibrium toward the product they want.
Note
Nothing stops at chemical equilibrium: molecules go on reacting in both directions, but because the two rates match, the amount of each substance holds steady. Change the temperature, the pressure or a concentration and the balance shifts until the rates match again at a new point.
Practice
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Origin
From Latin aequilībrium, formed from the word for "equal" and lībra ("balance").