inertia
Americannoun
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inertias
plural
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inertness, especially with regard to effort, motion, action, and the like; inactivity; sluggishness.
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Physics.
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the property of matter by which it retains its state of rest or its velocity along a straight line so long as it is not acted upon by an external force.
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an analogous property of a force.
electric inertia.
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Medicine/Medical. lack of activity, especially as applied to a uterus during childbirth when its contractions have decreased or stopped.
noun
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the state of being inert; disinclination to move or act
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physics
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the tendency of a body to preserve its state of rest or uniform motion unless acted upon by an external force
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an analogous property of other physical quantities that resist change
thermal inertia
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The resistance of a body to changes in its momentum. Because of inertia, a body at rest remains at rest, and a body in motion continues moving in a straight line and at a constant speed, unless a force is applied to it. Mass can be considered a measure of a body's inertia.
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See more at Newton's laws of motion See also mass
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of inertia
First recorded in 1705–15; from Latin: “lack of skill, slothfulness”; see inert, -ia
Explanation
Inertia is resistance to change. You hate looking at people's feet and yet you stay in your job as a shoe salesman year after year. Why? Inertia. Inertia is a physics term. Isaac Newtown discovered that a body at rest would stay at rest and a body moving through space would continue moving through space unless an external force (like friction or gravity) caused it to slow down or stop. Sometimes we need an external force to help us get going or to change direction, too, like a friend to tell us to get off the couch or to quit that job at the shoe store.
Vocabulary lists containing inertia
The Watsons Go to Birmingham
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The Things They Carried
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"The Hill We Climb," by Amanda Gorman
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
I still can’t say with certainty why this prosecution was perpetuated—what portion was attributable to the motivations of individual government agents and what portion to forces of institutional inertia.
From The Wall Street Journal ● Oct. 2, 2026
It’s about inertia and abdication, not solutions, and while I don’t entirely love this strange comedy, I’m giddy that it’s lurched into existence.
From Los Angeles Times ● Sep. 29, 2026
This inertia is terrible news for the Premier League as a competition.
From BBC ● Sep. 27, 2026
If it is as simple as directing your agent to find the highest yield, then the inertia that used to protect financial institutions is going away.
From The Wall Street Journal ● Sep. 24, 2026
Her voice had become sharp with overtones of bleakness as her soul congealed and she ceased to move, as the instinctive, omnipresent film of great weight, of an almost absolute inertia, settled over her.
From "Do Androids Dream of Electric Sheep?" by Philip K. Dick
The pigs on my either hand had by this time overcome their respective inertias and were chomping cheek-murdering chunks.
From The Enormous Room by E. E. (Edward Estlin) Cummings
That as the bird wing is a screw in action, and acts directly between the inertias of the load and the air, the position and operation of the screw, to the load, must imitate it.
From Scientific American Supplement, No. 443, June 28, 1884 by Various
We alternate between spasms of Virtue and comfortable inertias of Don't-care-a-Damn!
From Port O' Gold A History-Romance of the San Francisco Argonauts by Louis J. (Louis John) Stellman
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Get a wordDefinitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
