What are the units for inertia?

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    Inertia Units
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Discussion Overview

The discussion revolves around the units of inertia and the distinction between inertia and moment of inertia. Participants explore the definitions and implications of these concepts within the context of physics.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that inertia does not have specific units, while others claim it is equivalent to mass (kg), and moment of inertia is expressed in kg·m².
  • Inertia is described as the resistance to linear acceleration by a force, whereas moment of inertia is characterized as the resistance to angular acceleration by torque.
  • There is a discussion about the ambiguity of the term "inertia," with some participants questioning whether it refers to mass or momentum.
  • One participant emphasizes that inertia and moment of inertia have different definitions and units, arguing that inertia is a distinct property despite sharing units with mass.
  • Another participant suggests that the units for inertia could be expressed as kg·m²/s², although this claim is not universally accepted in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on whether inertia has units and what those units might be. There is no consensus on the definitions and implications of inertia versus moment of inertia, leading to ongoing debate.

Contextual Notes

The discussion highlights the potential confusion surrounding the terminology used in physics, particularly regarding the terms "inertia" and "moment of inertia," and their respective definitions and units.

miniradman
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Hello there, there have been a lot of conflicts between my physics teachers and university lecturers about the the units for intertia. Some say there aren't any units for inertia, and others say that it's in n/s. However, I don't know who to believe anymore... that's why I'm here :smile:

Also, if there aren't any units for inertia, why is that? Also, does "moment of inertia" differ from "inertia"? If so, how and why?

cheers - miniradman
 
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The unit for inertia is the same as the units for mass, kg, the unit of moment of inertia is $$ kg.m^{2}$$

Inertia is the resistance to linear acceleration by a force applied to the body.

Moment of inertia is the resistance to angular acceleration by torque applied to the body.
 
Last edited:
Or as they say: "Mass is a measure of inertia"
 
rollcast said:
Inertia is the resistance to linear acceleration by a force applied to the body.

Moment of inertia is the resistance to angular acceleration by torque applied to the body.

Miniradman: I find it surprising your professors find the point debatable. I think rollcast's answer is pretty unambiguous.

If you find it easier to start with a slightly less mathematical definition, mass determines how hard it is change a body's translational motion. Moment of inertia is determines how hard it is to change a body's rotational motion.
 
Fewmet said:
Miniradman: I find it surprising your professors find the point debatable. I think rollcast's answer is pretty unambiguous.
rollcast's answer may be unambiguous, but the term "inertia" is not. Does it mean mass or momentum? That's why you won't see the term used much in physics texts. Why use an ambiguous term when there are perfectly good, unambiguous alternatives (i.e., mass and momentum)?
 
Hear hear.
 
inertia is unambiguous

D H said:
rollcast's answer may be unambiguous, but the term "inertia" is not. Does it mean mass or momentum? That's why you won't see the term used much in physics texts. Why use an ambiguous term when there are perfectly good, unambiguous alternatives (i.e., mass and momentum)?

First there are two terms: Inertia vs. Moment of Inertia
Second, they have different units: kg vs. kg*m2 as rollcast posted.
Third, they are different from mass or anything else:
Inertia - The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force
Mass - a collection of incoherent particles, parts, or objects regarded as forming one body
Fourth, they are not mass or momentum, it has its own property. Even though the Inertia has the same unit as mass, the concept is different. The Moment of Inertia does not even have the same unit as momentum.
 

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