# Difference between momentum and linear inertia

• sycircle
In summary: I have never heard of 'linear inertia'. Is it a real thing? And if so, what does it mean?Linear inertia is a term used in Newton's Laws of Motion. It is the resistance an object has to changes in velocity.
sycircle
Hi everyone, I have always been confused by momentum and linear inertia. What exactly is the difference between them? Aren't them both resistance to change in motion? Its hard to explain what I am confused with so here's an example: if there are 2 moving cars traveling at the same speed and car A has a greater mass than car B, why would it be more difficult to stop car A than car B? Is it because car A has greater inertia or is it because car A has greater momentum? I can't distinguish between them two. Could someone please help me? and please explain why it is one but not the other.
Thank you so much!

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sycircle said:
Hi everyone, I have always been confused by momentum and linear inertia. What exactly is the difference between them? Aren't them both resistance to change in motion? Its hard to explain what I am confused with so here's an example: if there are 2 moving cars traveling at the same speed and car A has a greater mass than car B, why would it be more difficult to stop car A than car B? Is it because car A has greater inertia or is it because car A has greater momentum? I can't distinguish between them two. Could someone please help me? and please explain why it is one but not the other.
Thank you so much!

I must admit I never use the word "inertia". Inertia is simply mass by another name. It's not momentum anyway.

PeroK said:
I must admit I never use the word "inertia". Inertia is simply mass by another name. It's not momentum anyway.
But what's the difference between the two? Thank youu

sycircle said:
But what's the difference between the two? Thank youu

You mean the difference between mass and momentum?

sophiecentaur
PeroK said:
You mean the difference between mass and momentum?
I meant the difference between linear inertia and momentum. I thought linear inertia does exist though? and it's different from mass?? Please correct me if I am wrong I am really confused by linear inertia, momentum and mass...

sycircle said:
I meant the difference between linear inertia and momentum. I thought linear inertia does exist though? and it's different from mass?? Please correct me if I am wrong I am really confused by linear inertia, momentum and mass...

Well, if I've got to where I am and never heard of "linear inertia", it can't be very important! I suspect it's a fancy phrase for ... mass!

sophiecentaur
PeroK said:
Well, if I've got to where I am and never heard of "linear inertia", it can't be very important! I suspect it's a fancy phrase for ... mass!
I see... thank you for helping :)

Inertia is never defined in textbooks of basic mechanics so I am reluctant to use it or to have much of an opinion about it - other than it is often used instead of 'mass', but to sound more meaningful for some people.
Momentum is certainly not a 'reluctance to change Momentum but Mass could be though of as a reluctance to change momentum (In Newton's Laws of Motion - somewhere?)

In common usage, the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), or sometimes to its momentum, depending on the context. The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his First Law of Motion: that an object not subject to any net external force moves at a constant velocity. Thus, an object will continue moving at its current velocity until some force causes its speed or direction to change.

Above from wikipedia

sycircle
mathman said:
Above from wikipedia
The clue, here, is the phrase "In common usage". Physics terms are physics terms and common usage frequently gets it hideously wrong. By 'wrong' I mean that the terms do not follow consistent rules when 'used commonly' and cause confusion. This is an example where Wiki gets mixed with Dictionary definitions. Mostly, Wiki does better.

An object can have a lot of inertia even if it is not moving at all. It would resist any force to accelerate it. But it would have no momentum.

sycircle
FactChecker said:
An object can have a lot of inertia even if it is not moving at all. It would resist any force to accelerate it. But it would have no momentum.
Can you give a definition, which could be used in an equation of motion, for instance? What could be done to measure the inertia that the object you are quoting actually has? Without that, inertia is not a quantity that can be used, validly, in Physics.

Sounds to me like the tail wagging the dog.
We spent hundreds of years trying quite successfully to formalise our Science. What, then, is the point of trying to slot into that structure, a word that just doesn't fit? Who benefits from that?
If this were a creative writing forum, then I would be all in favour but PF is supposed to be a PF.

FactChecker
sophiecentaur said:
Sounds to me like the tail wagging the dog.
We spent hundreds of years trying quite successfully to formalise our Science. What, then, is the point of trying to slot into that structure, a word that just doesn't fit? Who benefits from that?
If this were a creative writing forum, then I would be all in favour but PF is supposed to be a PF.

sophiecentaur
sophiecentaur said:
Sounds to me like the tail wagging the dog.
We spent hundreds of years trying quite successfully to formalise our Science. What, then, is the point of trying to slot into that structure, a word that just doesn't fit? Who benefits from that?
If this were a creative writing forum, then I would be all in favour but PF is supposed to be a PF.
So, inertia does not exist as a physics term? It is mass that I am supposed to be concerning? and please correct me if I am wrong: mass is a resistance to acceleration and momentum is the tendency for an object to keep moving. If this is correct then what is the difference between mass and momentum? thank you

sycircle said:
what is the difference between mass and momentum?
Look at their precise mathematical definitions, instead of hand wavy descriptions.

sycircle said:
and momentum is the tendency for an object to keep moving
Why not look up the definition, rather than waving your hands about? Momentum is one of the very fundamental quantities in Physics and it is defined Exactly.

## What is the difference between momentum and linear inertia?

Momentum and linear inertia are two important concepts in physics that are often confused with each other. While they are related, they have distinct definitions and applications.

## How are momentum and linear inertia related?

Momentum is a measure of an object's motion, while linear inertia is a measure of an object's resistance to changes in motion. This means that the momentum of an object is directly related to its linear inertia.

## What is the formula for calculating momentum?

The formula for momentum is p = m x v, where p is momentum, m is mass, and v is velocity. This means that an object with a larger mass or a higher velocity will have a greater momentum.

## How is linear inertia affected by mass and velocity?

The linear inertia of an object is directly proportional to its mass and its velocity. This means that an object with a larger mass or a higher velocity will have a greater linear inertia, making it harder to change its state of motion.

## What are some real-world applications of momentum and linear inertia?

Momentum and linear inertia are important concepts in many fields, including sports, transportation, and engineering. For example, in sports, athletes use their momentum to increase their speed and power, while engineers use linear inertia to design structures and vehicles that can withstand different forces and motions.

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