# The Naked Scientists Forum

### Author Topic: MOMENTUM......what exactly is it ?  (Read 2859 times)

#### neilep

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##### MOMENTUM......what exactly is it ?
« on: 13/05/2007 23:10:48 »
Hi ya All,

Hope you're all well !!

Momentum is a thing that keeps things moving when they have been pushed to a velocity and then the force is stopped and they keep on moving yes ?

But....*frustrated at inability to explain adequately*.....what is it ?...is a like a light wave ?...can it exist without a thing for it to be associated with ?....why does it die out ?...where does it go ?

Does it then add weight/mass to the thing it is propelling  ?

Yours....(wishing I never attempted to ask such a thing)..Neil
xxx
« Last Edit: 13/05/2007 23:14:09 by neilep »

#### lyner

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##### MOMENTUM......what exactly is it ?
« Reply #1 on: 13/05/2007 23:36:41 »
Stick with the standard definition, rather than trying to get a 'feel' for what it is.
Momentum = mass times velocity
or - if it's a photon, you're talking about
Momentum = h/wavelength (where h is the planck constant)
The clever thing about using momentum in calculations is that it is 'conserved' in collisions, which allows you to  predict what will happen.
Trying to say what momentum 'is' is a bit like trying to define electrical resistance without just saying
resistance = Potential difference / current
It leads to a lot of chat without any useful  conclusion.

#### another_someone

• Guest
##### MOMENTUM......what exactly is it ?
« Reply #2 on: 14/05/2007 06:54:00 »
Hi ya All,

Hope you're all well !!

Momentum is a thing that keeps things moving when they have been pushed to a velocity and then the force is stopped and they keep on moving yes ?

But....*frustrated at inability to explain adequately*.....what is it ?...is a like a light wave ?...can it exist without a thing for it to be associated with ?....why does it die out ?...where does it go ?

Does it then add weight/mass to the thing it is propelling  ?

Yours....(wishing I never attempted to ask such a thing)..Neil
xxx

In essence, momentum is intimately bound with mass, and one cannot exist without the other.

Not sure what you mean by "why does it die out?" - it does not die out, it cannot be die out.  What it can do it be spread around a bit, so that what started out as being momentum associated with a large lump of lead, might end up being spread around all the atoms of air around the room; but it never dies out.

#### lyner

• Guest
##### MOMENTUM......what exactly is it ?
« Reply #3 on: 14/05/2007 10:41:55 »
Quote
..why does it die out ?.
Momentum is one of those things that really don't "die out".
It gets shared out, if you like, amongst other objects - like air molecules - that your object may bump into. BUT it is conserved, as they say.
When they look at pictures of 'fundamental'  particle collisions in particle accelerators, they  use this 'conservation law' to decide on the  masses / energies of particles which have left traces and particles that haven't, even.
When you watch snooker on TV you can see momentum conservation at work at every collision.  Over short distances, the friction doesn't reveal itself but, when it does, the momentum is being transferred to the table / world as the ball slows down.

#### The Naked Scientists Forum

##### MOMENTUM......what exactly is it ?
« Reply #3 on: 14/05/2007 10:41:55 »