Inertia vs Momentum: What’s the Key Difference?

[Mozart]

Are momentum and inertia kind of the same thing? I don't understand the big difference between them. The only difference I can see is that for instance my chair isn't moving but it has inertia since I would have to apply such a force to get it moving. However, I don't think I can say it has momentum right now. If a ball is rolling towards me then I feel as if I can say it has momentum and it has inertia, and in my mind I can't see the difference between them.

Please help. Thanks

 

[Mk]

Inertia is a property of matter, but matter at rest has what momentum?

 

[Mozart]

What do you mean by at rest? Constant velocity or zero velocity.

 

[cepheid]

What do you mean by at rest? Constant velocity or zero velocity.

Only one of those two choices accurately describes a state of being "at rest." I'll give you two guesses which one...

 

[G01]

Inertia cannot be tranferred to another body while momentum can.

If you push something and get it moving it does not loose inertia, and you do not gain any inertia.

Where as when you push something forward, the object does gain positive momentum. You will also move the opposite way and gain negative momentum. And both object gain momentum and still adhere to the conservation of momentum.

 

[pmb_phy]

Inertia is a property of matter, but matter at rest has what momentum?

Inertia is that quantity which resists the changes in momentum of an object. A particle sitting still willl still resist changes in momentum.

Pete

 

[bobbytkc]

Inertia is the resistance of a massive object to changes in its acceleration. It is just a word used to say that it is difficult to make an object go faster, even though we don't really understand why.

Momentum, unlike inertia, is actually a vector quantity that gives measurement to the total amount of motion in a direction. An object twice as massive but moving in the same speed and direction has twice as much motion in that direction. An object moving twice as fast as another in the same direction, but have the same mass, has twice as much motion in that particular direction.

So in short, inertia is a property of massive objects, momentum is the measurement of a separate property (motion) of massive objects.

 

[lovetosinger]

Are momentum and inertia kind of the same thing? I don't understand the big difference between them. The only difference I can see is that for instance my chair isn't moving but it has inertia since I would have to apply such a force to get it moving. However, I don't think I can say it has momentum right now. If a ball is rolling towards me then I feel as if I can say it has momentum and it has inertia, and in my mind I can't see the difference between them.

Please help. Thanks

i am still wondering the same thing because i have this weird homework paper that's hard

 

[lovetosinger]

Inertia cannot be tranferred to another body while momentum can.

If you push something and get it moving it does not loose inertia, and you do not gain any inertia.

Where as when you push something forward, the object does gain positive momentum. You will also move the opposite way and gain negative momentum. And both object gain momentum and still adhere to the conservation of momentum.

thanks that really helps

 

[lovetosinger]

thanks go1 what you said about momentum and inertia helped me! :) !

 

[lovetosinger]

what school do youguys go 2

 

[willyadventur]

Um Ok

But if you push a ball it initially has some inertia to over come to get it moving, but once it is rolling, because it is now spinning around, doesn’t gain inertia (which it must give up/transfer to something when it comes to a rest)? Or am I way off here?

The three types of inertia are

(1) The general concept of inertia, according to Newton's first laws, concerning objects' masses when it comes to resistance.
(2) Rotational inertia
(3) Gyroscopic inertia

SO a ball rolling down a has gained inertia and momentum?

Willy

 

[russ_watters]

This thread is very old and we've had more recent discussions, but..

Um Ok

But if you push a ball it initially has some inertia to over come to get it moving, but once it is rolling, because it is now spinning around, doesn’t gain inertia (which it must give up/transfer to something when it comes to a rest)? Or am I way off here?

Objects do not gain inertia unless they gain mass.

SO a ball rolling down a has gained inertia and momentum?

No, it has only gained momentum.

 

[HallsofIvy]

"Inertia" is mass.

"Momentum" is mass times velocity.

 

[harrylin]

Are momentum and inertia kind of the same thing? I don't understand the big difference between them. The only difference I can see is that for instance my chair isn't moving but it has inertia since I would have to apply such a force to get it moving. However, I don't think I can say it has momentum right now. If a ball is rolling towards me then I feel as if I can say it has momentum and it has inertia, and in my mind I can't see the difference between them.

Please help. Thanks

Inertia and mass are nearly the same thing (although not exactly). And as you know, momentum is mass times speed.

That's even so in relativity if you use the relativistic mass definition: then "inertia" is simply the inertial property of mass when you try to change an object's velocity - it's the resistance to that attempt.
If you use the rest mass definition of mass, then "inertia" is the inertial property of mass times the relativistic gamma factor.I now see that it was a very old thread, here's a quick comment on the new post:

Um Ok

But if you push a ball it initially has some inertia to over come to get it moving, but once it is rolling, because it is now spinning around, doesn’t gain inertia (which it must give up/transfer to something when it comes to a rest)? Or am I way off here?
[..] according to Newton's first laws [..]
SO a ball rolling down a has gained inertia and momentum?

Willy

No, in classical physics it doesn't gain inertia. But see my comments here above.

Harald

 

[david90]

If an object has inertia of 10 kg*m^2, what does this physically mean? For example, if an object travels at 10 m/s, then in my head I can see that the object travels 10 m every sec. I guess I'm having problem understanding what kg*m^2 really mean.

 

[PeterBo]

The higher Inertia an object has the more force you need to apply to alter it's velocity / placement in space.
Simply put.

 

[Ryan_m_b]

Yes;

Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass.

http://en.wikipedia.org/wiki/Inertia

EDIT: Peterbo I didn't realize that you had posted on an old thread when I replied. Looking back you can see that this thread is many years old. In future if you want to ask something feel free (in fact it is preferred) to start a new thread rather than resurrecting an old one.

 

[russ_watters]

If an object has inertia of 10 kg*m^2, what does this physically mean? For example, if an object travels at 10 m/s, then in my head I can see that the object travels 10 m every sec. I guess I'm having problem understanding what kg*m^2 really mean.

That is moment of inertia, which is resistance to angular acceleration. It has nothing to do with linear speed.

 

[PeterBo]

Yes;

http://en.wikipedia.org/wiki/Inertia

EDIT: Peterbo I didn't realize that you had posted on an old thread when I replied. Looking back you can see that this thread is many years old. In future if you want to ask something feel free (in fact it is preferred) to start a new thread rather than resurrecting an old one.

I did notice it was started a long time ago.
How ever others have been replying to it recently :)
Im new in the forums as you can see, my first post. Just wanted to post a reply to this rather simple question, since some posters in it couldn't see the awnser when told in it's mathmatical form.

Thank you
/Peter

 

[sophiecentaur]

A rolling stone gathers no inertia?

For classical mechanics, who needs ever to use the word 'inertia'? 'Inertia' is so near 'mass' so why not just use the term Mass? There is enough misuse of mechanics terms and ideas that we should try to avoid confusion when we can by limiting the number of terms we use.

 

[Oldfart]

A rolling stone gathers no inertia?

For classical mechanics, who needs ever to use the word 'inertia'? 'Inertia' is so near 'mass' so why not just use the term Mass? There is enough misuse of mechanics terms and ideas that we should try to avoid confusion when we can by limiting the number of terms we use.

What, specifically, are the differences between inertia and mass?

 

[sophiecentaur]

Dunno. I tend only to deal with classical mechanics, with any amount of confidence, and i never use the word Inertia.
What a whimp!

 

[aman kapoor]

Are momentum and inertia kind of the same thing? I don't understand the big difference between them. The only difference I can see is that for instance my chair isn't moving but it has inertia since I would have to apply such a force to get it moving. However, I don't think I can say it has momentum right now. If a ball is rolling towards me then I feel as if I can say it has momentum and it has inertia, and in my mind I can't see the difference between them.

Please help. Thanks

I
Inertia is the property of a body to resist the change in its state of motion or the rest, but momentum is the amount of motion contained the body.
Suppose a there is body ,if it is moving it has an inertia of motion , and if it is a static body then it ,has an inertia of rest .
Both have two different forms of inertia but the momentum is only with a moving body.
Inertia only depends upon the mass but the momentum not only depends on the mass but also the velocity.
Basically inertia of motion is to resist the change in state of motion, that is why you have to apply the force to stop or change the direction of that body but momentum is the measure of that motion , which telly you how much force you should apply and in which direction to change that state of motion.
When a bullet is moving , to stop it we do not require a lot of force . Even a hanging block of wood would do , because its mass is not very big , but it pierce through the wood due to its velocity , not the inertia.

 

[sophiecentaur]

I think the above is very much a personal view. Is there anything you could quote as a reference for it?

 

[willyadventur]

My basic question is when a moving object collides with a stationary object, in a non elastic collision, how much mass does the stationary object have to have to cause both objects to remain stationary after impact; cause the colliding object to rebound, cause the colliding object to remain stationary and the at rest object to rebound, for both objects to objects to rebound off of each other; and for both the at rest and colliding objects to both travel in the same direction.

Does this depend on the mass of the stationary object compared to the mass of the colliding object only, or is it the total momentum of the colliding object irrespective of its mass?

Also for an object to move their must be an imbalance in force, correct. So an impulse of 9.8 N.s = a momentum change of 9.8Kg.M/s and an acceleration force of 1Kgm/s^2 which equals 9.8 Newtons of force.

To answer my own question I think it only depends on the mass of the stationary and colliding objects (see example below). But I can’t account for at what point both objects will rebound off each other? (So If I consider the total inertia of the colliding object compared to the mass of the stationary object, it must have something to do with the length of time the shock wave (impusle) takes to ‘reflect’ of the opposite end of the stationary object and transfer back to the colliding object and with enough force (in N.s or N or Pa pressure?) to overcome the Mass of the colliding object and/or any left over momentum, aftter collision, of the coliding object?)

- Mass colliding object < Stationary objects mass (Kg) + static friction = colliding object rebound
- Mass colliding object = Stationary object mass (Kg) + static friction = both objects remain stationary.
- Mass colliding object > Stationary object mass + static friction + = both stationary and colliding objects to move in the direction of applied force together.

- In the absences of friction, if the both objects remained stationary after collision, or did not deform, then the force of the impulse wave would cause either, or both objects, to disintegrate, so the did move, for wants of better words.

 

[sophiecentaur]

No amount of mass will keep the stationary object exactly stationary. Momentum is conserved in any collision. So one small object with mass m at big velocity V will result in small and big object (mass M) moving off at very small v
such that
mV = (M+m)v
v is always finite.