inertia

American  

[in-ur-shuh, ih-nur-] / ɪnˈɜr ʃə, ɪˈnɜr- /

noun

1. inertness, especially with regard to effort, motion, action, and the like; inactivity; sluggishness.

   Synonyms:

   laziness, inaction, torpor

2. Physics.

   1. 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.

   2. an analogous property of a force.

      electric inertia.

3. Medicine/Medical. lack of activity, especially as applied to a uterus during childbirth when its contractions have decreased or stopped.

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inertia British  

/ ɪnˈɜːʃə, -ʃɪə /

noun

1. the state of being inert; disinclination to move or act

2. physics

   1. the tendency of a body to preserve its state of rest or uniform motion unless acted upon by an external force

   2. an analogous property of other physical quantities that resist change

      thermal inertia

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inertia Scientific  

/ ĭ-nûr′shə /

1. 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.

2. See more at Newton's laws of motion See also mass

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inertia Cultural  

1. In physics, the tendency for objects at rest to remain at rest, and for objects in uniform motion to continue in motion in a straight line, unless acted on by an outside force. (See Newton's laws of motion.)

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Other Word Forms

• inertial
  adjective
• noninertial
  adjective

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.

Example Sentences

Professors who are Luddites or have used the same syllabus for years sometimes struggle to get out of that state of inertia, Cook said.

From The Wall Street Journal • May 18, 2026

Even if the state awards more funding for the tribe’s restoration efforts, he said, interruptions to science damage trust and relationships — creating setbacks and inertia that are difficult to recover from.

From Los Angeles Times • Apr. 4, 2026

The major human spaceflight programs are supertankers, with tremendous inertia.

From Slate • Mar. 13, 2026

While options exist already for individuals to open their own retirement plans through IRAs, people often get stymied by the administrative hurdles and their own inertia and fail to create such accounts, experts said.

From MarketWatch • Feb. 25, 2026

The same phrase is then employed by Newton in his definition of inertia; he evidently took the phrase from Descartes, and discovered only later that it originated in Lucretius.

From "The Invention of Science" by David Wootton

Related Words

• apathy
• laziness
• paralysis
• passivity
• sluggishness