| Topic: |
Science > Physics |
| User: |
"Mark Teller" |
| Date: |
01 Jun 2007 06:49:08 AM |
| Object: |
Energy loss and momentum conservation |
I have read that in collisions and particle interactions, even if
energy loss takes place, momentum remains conserved.
In general how is energy loss handled in classical mechanics?
For example, two masses connected by a spring and at rest is hit by a
projectile at instant A. It hits one of the masses resulting in the
two mass object to spin.
It also sets up an oscillatory motion causing the masses to move
towards and away from each other.
Eventually due to energy losses in the spring the rotational motion
comes to a stop at instant B.
How would you explain the angular momentum difference between instant
A and B?
Thanks
Mark
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| User: "Greg Neill" |
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| Title: Re: Energy loss and momentum conservation |
01 Jun 2007 08:02:24 AM |
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"Mark Teller" <markteller2000@yahoo.com> wrote in message
news:1180698548.638936.146980@z28g2000prd.googlegroups.com...
I have read that in collisions and particle interactions, even if
energy loss takes place, momentum remains conserved.
In general how is energy loss handled in classical mechanics?
For example, two masses connected by a spring and at rest is hit by a
projectile at instant A. It hits one of the masses resulting in the
two mass object to spin.
It also sets up an oscillatory motion causing the masses to move
towards and away from each other.
Eventually due to energy losses in the spring the rotational motion
comes to a stop at instant B.
How would you explain the angular momentum difference between instant
A and B?
If the two object ensemble is in free space, it's not
clear that rotational motion will come to a halt at
any time, there being no mechanism to bleed off
angular momentum to the surroundings.
Any mechanism that removes momentum carries it away,
so momentum is conserved. This includes frictional
losses where the energy is lost to heat -- even
photons carry momentum.
.
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| User: "PD" |
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| Title: Re: Energy loss and momentum conservation |
01 Jun 2007 12:09:55 PM |
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On Jun 1, 6:49 am, Mark Teller <markteller2...@yahoo.com> wrote:
I have read that in collisions and particle interactions, even if
energy loss takes place, momentum remains conserved.
Energy is not lost. It is just transformed into one or more forms that
are not necessarily recoverable mechanical energy. Examples of the
latter are heat, sound, or structural deformation, all of which occur
in a car crash, for example.
What is different between momentum and energy is that the latter can
freely exchange among all the forms available to it, whereas the
former does no such exchange of form. For example, linear kinetic
energy can freely turn into rotational kinetic energy. However, linear
momentum does NOT exchange with angular momentum.
In general how is energy loss handled in classical mechanics?
For example, two masses connected by a spring and at rest is hit by a
projectile at instant A. It hits one of the masses resulting in the
two mass object to spin.
It also sets up an oscillatory motion causing the masses to move
towards and away from each other.
Eventually due to energy losses in the spring the rotational motion
comes to a stop at instant B.
How would you explain the angular momentum difference between instant
A and B?
The energy losses in the spring are not responsible for the stopping
of the rotation. They just happen to occur at the same time and likely
both due to a *third* and unaccounted-for influence, which could be
any number of things, including air drag or friction with a surface
that the spring-coupled masses are sitting on.
PD
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| User: "Mark Teller" |
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| Title: Re: Energy loss and momentum conservation |
03 Jun 2007 12:17:41 PM |
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On Jun 1, 10:09 pm, PD <TheDraperFam...@gmail.com> wrote:
On Jun 1, 6:49 am, Mark Teller <markteller2...@yahoo.com> wrote:
I have read that in collisions and particle interactions, even if
energy loss takes place, momentum remains conserved.
Energy is not lost. It is just transformed into one or more forms that
are not necessarily recoverable mechanical energy. Examples of the
latter are heat, sound, or structural deformation, all of which occur
in a car crash, for example.
What is different between momentum and energy is that the latter can
freely exchange among all the forms available to it, whereas the
former does no such exchange of form. For example, linear kinetic
energy can freely turn into rotational kinetic energy. However, linear
momentum does NOT exchange with angular momentum.
In general how is energy loss handled in classical mechanics?
For example, two masses connected by a spring and at rest is hit by a
projectile at instant A. It hits one of the masses resulting in the
two mass object to spin.
It also sets up an oscillatory motion causing the masses to move
towards and away from each other.
Eventually due to energy losses in the spring the rotational motion
comes to a stop at instant B.
How would you explain the angular momentum difference between instant
A and B?
The energy losses in the spring are not responsible for the stopping
of the rotation. They just happen to occur at the same time and likely
both due to a *third* and unaccounted-for influence, which could be
any number of things, including air drag or friction with a surface
that the spring-coupled masses are sitting on.
PD
Whatever be the form of energy loss, if you agree that the rotation
does stop after sometime, how do you explain the momentum loss?
Thanks
Mark
.
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| User: "Eric Gisse" |
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| Title: Re: Energy loss and momentum conservation |
03 Jun 2007 01:11:16 PM |
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On Jun 3, 10:17 am, Mark Teller <markteller2...@yahoo.com> wrote:
On Jun 1, 10:09 pm, PD <TheDraperFam...@gmail.com> wrote:
On Jun 1, 6:49 am, Mark Teller <markteller2...@yahoo.com> wrote:
I have read that in collisions and particle interactions, even if
energy loss takes place, momentum remains conserved.
Energy is not lost. It is just transformed into one or more forms that
are not necessarily recoverable mechanical energy. Examples of the
latter are heat, sound, or structural deformation, all of which occur
in a car crash, for example.
What is different between momentum and energy is that the latter can
freely exchange among all the forms available to it, whereas the
former does no such exchange of form. For example, linear kinetic
energy can freely turn into rotational kinetic energy. However, linear
momentum does NOT exchange with angular momentum.
In general how is energy loss handled in classical mechanics?
For example, two masses connected by a spring and at rest is hit by a
projectile at instant A. It hits one of the masses resulting in the
two mass object to spin.
It also sets up an oscillatory motion causing the masses to move
towards and away from each other.
Eventually due to energy losses in the spring the rotational motion
comes to a stop at instant B.
How would you explain the angular momentum difference between instant
A and B?
The energy losses in the spring are not responsible for the stopping
of the rotation. They just happen to occur at the same time and likely
both due to a *third* and unaccounted-for influence, which could be
any number of things, including air drag or friction with a surface
that the spring-coupled masses are sitting on.
PD
Whatever be the form of energy loss, if you agree that the rotation
does stop after sometime, how do you explain the momentum loss?
Thanks
Mark
Look up friction in an introductory physics text. Folks here seem to
like Haliday and Resnick.
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| User: "PD" |
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| Title: Re: Energy loss and momentum conservation |
03 Jun 2007 03:01:12 PM |
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On Jun 3, 12:17 pm, Mark Teller <markteller2...@yahoo.com> wrote:
On Jun 1, 10:09 pm, PD <TheDraperFam...@gmail.com> wrote:
On Jun 1, 6:49 am, Mark Teller <markteller2...@yahoo.com> wrote:
I have read that in collisions and particle interactions, even if
energy loss takes place, momentum remains conserved.
Energy is not lost. It is just transformed into one or more forms that
are not necessarily recoverable mechanical energy. Examples of the
latter are heat, sound, or structural deformation, all of which occur
in a car crash, for example.
What is different between momentum and energy is that the latter can
freely exchange among all the forms available to it, whereas the
former does no such exchange of form. For example, linear kinetic
energy can freely turn into rotational kinetic energy. However, linear
momentum does NOT exchange with angular momentum.
In general how is energy loss handled in classical mechanics?
For example, two masses connected by a spring and at rest is hit by a
projectile at instant A. It hits one of the masses resulting in the
two mass object to spin.
It also sets up an oscillatory motion causing the masses to move
towards and away from each other.
Eventually due to energy losses in the spring the rotational motion
comes to a stop at instant B.
How would you explain the angular momentum difference between instant
A and B?
The energy losses in the spring are not responsible for the stopping
of the rotation. They just happen to occur at the same time and likely
both due to a *third* and unaccounted-for influence, which could be
any number of things, including air drag or friction with a surface
that the spring-coupled masses are sitting on.
PD
Whatever be the form of energy loss, if you agree that the rotation
does stop after sometime, how do you explain the momentum loss?
Thanks
Mark
Momentum is only conserved in *isolated systems*. In this case there
is an agent that is acting across the boundary of the system: friction
from an external surface. Now if you take the surface AND the
projectile AND spring-coupled masses, and those are isolated, then
angular momentum of that whole system will be conserved. For example,
in the interaction between the surface and the two-mass system,
whatever angular momentum lost by the two-mass system will be picked
up by the surface. Because the surface is so massive, this momentum
transfer will not necessarily result in a noticeable angular velocity.
PD
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