inertia
Americannoun
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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.
Inertia is the easiest and most likely choice in any polity, and sometimes not even a crisis is enough to dislodge a dysfunctional status quo.
From The Wall Street Journal • Feb. 12, 2026
Inertia on the issue of cats will lead to further extinctions.
From New York Times • Apr. 25, 2019
Inertia may be enough to keep a statue in the ground, but it’s not going to make anybody care about the president on that statue.
From Salon • Feb. 6, 2016
Inertia is the tendency of an object to remain at rest or remain in motion.
From Textbooks • Aug. 12, 2015
Inertia is possessed quite as much by a moving body as a body at rest.
From Aether and Gravitation by Hooper, William George
Definitions 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.
