Are Inertia and Momentum the Same in Physics?

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Discussion Overview

The discussion revolves around the relationship between inertia and momentum in physics, exploring their definitions, properties, and whether they can be considered the same. The scope includes conceptual clarifications and technical explanations.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that momentum is defined as the product of mass and velocity (p = mv).
  • Others argue that inertia is more closely related to mass and is a property of an object that resists changes in its state of motion or rest.
  • One participant suggests that momentum can be seen as a measure of inertia, while noting that inertia itself does not have a numerical value.
  • There is a claim that inertia is unchanging, whereas momentum can vary, particularly in classical mechanics.
  • Another participant questions whether velocity should be considered part of inertia, reasoning that an object's speed affects how difficult it is to change its state.
  • One participant challenges the idea that inertia can be equated with momentum, emphasizing that a stationary object has less momentum despite potentially being equally hard to stop as a fast-moving object.
  • A formal definition for inertia is proposed, relating it to the force or torque required to change an object's velocity or angular velocity.
  • One participant disputes the notion that velocity is a component of inertia, referencing Newton's second law (f=ma) to argue that it does not include velocity terms.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between inertia and momentum, with no consensus reached on whether they are the same or how they should be defined. The discussion remains unresolved regarding the definitions and implications of both concepts.

Contextual Notes

Some limitations include the dependence on definitions of inertia and momentum, as well as the potential implications of relativity, which are noted but not explored in detail.

student85
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Are they the same thing?
momentum = p = mv
 
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Inertia is more like m
 
Interia has no numerical value unlike momentum. It's just a property of an object based on its mass.
 
Ok, that's what I thought. But then, how would you define momentum? (in words)
 
"momentum is the measure of inertia "
and inertia is the property of the system or the object to resist a change in its state i.e either the state of motion or of rest
 
"momentum is the measure of inertia "

Inertia is unchanging whereas momentum can be changing. (for all classical approx.)

momentum is concerned with moving things.
 
Inertia is related to mass. Momentum is related to mass and speed (as the equation shows).
 
Virtual said momentum is the measure of inertia.
Then, velocity must be part of inertia. I think it makes sense since the faster the object is going, the harder it is to change its condition...am I right?
 
student85 said:
Virtual said momentum is the measure of inertia. [That] makes sense since the faster the object is going, the harder it is to change its condition...

I wouldn't equate inertia with momentum. It's just as hard to stop a fast object as it is, after stopping it, to then speed the object back up again, however the stationary object has infinitely less momentum.

Perhaps a formal definition for inertia (or moment of inertia) should be the force (or torque) with which an object resists a change in its velocity (or in its angular velocity). Consequently, the SI unit for inertia would be kg (or, er, kgm^2/rad).
 
  • #10
student85 said:
Virtual said momentum is the measure of inertia.
Virtual was wrong to say that because...
Then, velocity must be part of inertia. I think it makes sense since the faster the object is going, the harder it is to change its condition...am I right?
No, you are clearly not right as f=ma doesn't say anything about velocity, does it? If it got harder to change velocity when speed was higher, those terms should appear in that equation.

(caveat: relativity not needed here)
 

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