Darren New wrote:
> Paul Fuller wrote:
>> If 'No' then please provide an explanation or link explaining how any 
>> form of energy can be turned into angular momentum in a closed system.
> 
> Hold your cat upside down, then drop him. ;-)
> 
Is that with or without buttered toast attached to its back :)

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Paul Fuller <pgf### [at] optusnetcomau> wrote:
> Sorry but you are just wrong.

  It's easy to say "you are just wrong" without actually explaining why.

> In this case you assert that there is a point at which the cables can be 
> attached that will prevent the stopping action from imparting any spin 
> to the parent body.

  Attach the cable to the opposite side of the parent body. What happens?

  Besides, we can just forget the cable: Simply shoot the projectile and
that's it. With the correct amount of speed it will stop the object from
rotating. Where did the angular momentum go?

> No system of cables, pulleys, magnets, gyroscopes, friction, 
> electricity, radiation, carbon nonotubes, superconductors or whatever 
> can alter that.

  Since a spinning object can be used to produce energy (eg. by friction)
you are effectively saying that a spinning object is an infinite source
of energy because its angular momentum will never disappear.

-- 
                                                          - Warp

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Paul Fuller <pgf### [at] optusnetcomau> wrote:
> >   In order for the rotating secondary object to affect the primary object's
> > rotation, it has to be connected to the primary object somehow. This
> > connection causes friction.
> It has to exert a force and I agree that some energy will be lost in any 
> practical system.  You are just not getting the point that friction 
> itself has nothing to do with angular momentum.

  So you are effectively saying that regardless of heat produced by
friction, angular momentum is always conserved. This would effectively
make a spinning object an infinite source of energy.

> >   This would be true in a completely friction-free system. The thing is,
> > friction dissipates part of this energy.
> Still hung up on friction !

  A spinning object can be used to produce heat by friction.

> True enough.  Friction is the mechanism that takes energy from the 
> spinning Earth.

  Where does this energy come from?

>  At the same time there is a change elsewhere in the 
> system that conserves angular momentum overall.

  Which means that the energy was produced completely for free?
Isn't that kind of the definition of a perpetual motion machine?

> The tidal locking effect is well known and you have described it 
> reasonably well.  However you are wrong to say that angular momentum is 
> converted to heat by friction.

  Then what is it that is converted to heat by friction?

> Angular momentum is a different thing to energy.  Sorry but there is no 
> known way to convert one to another.  You can certainly use energy to 
> start one mass spinning.  Thing is that there must be an opposite amount 
> of angular momentum showing up somewhere else.

  Two objects with no angular momentum at all collide off-center, and
they get stuck to each other. The resulting union of masses will start
spinning because of the collision.

  Somewhere else in the universe something else starts spinning in the
opposite direction due to a magical universal conservation of angular
momentum law.

  Yes, I understand perfectly now. Thanks for clearing that up.

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
>   Besides, we can just forget the cable: Simply shoot the projectile and
> that's it. With the correct amount of speed it will stop the object from
> rotating. Where did the angular momentum go?

  I thought about this and became to a conclusion. You could have explained
it if you knew it instead of just saying "you are wrong" without any
explanation.

  The answer is that the object-projectile system still has the angular
momentum. If we calculate the angular momentum of this system after the
firing, ie. the how the system is oriented with regard to the center of
mass of the system and the distance between the two objects, we will
probably get an angular momentum equivalent to the original one.

  The same is probably true for two approaching objects which collide.
Even though each object by itself didn't have any angular momentum, the
two-object system did. The entire two-object system is actually rotating
around the center of mass of the two objects (even though they two objects
are travelling almost rectilinearly; this is because they are not travelling
along the same line in space). When they collide and stick to each other,
the "speed of rotation" they had just before they collided will be kept. The
angular momentum will be unmodified. Only if the two objects were travelling
exactly on the same line in space will there be no rotation because there's
no angular momentum.

-- 
                                                          - Warp

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scott <sco### [at] laptopcom> wrote:
> > http://www.xkcd.com/162/

> "Each turn robs the planet of angular momentum"

> Unfortunately not...

  Maybe the idea was that *while* she is spinning, the Earth rotates more
slowly, making the day longer? When she stops spinning the rotation of the
Earth may return to normal, but that day will still have been longer
nevertheless.

-- 
                                                          - Warp

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On Sun, 28 Oct 2007 11:00:57 +0100, Warp <war### [at] tagpovrayorg> wrote:
>   Maybe the idea was that *while* she is spinning, the Earth rotates more
> slowly, making the day longer? When she stops spinning the rotation of  
> the
> Earth may return to normal, but that day will still have been longer
> nevertheless.


Yeah, but she will have spent it spinning...



-- 
FE

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Warp wrote:
> Warp <war### [at] tagpovrayorg> wrote:
>>   Besides, we can just forget the cable: Simply shoot the projectile and
>> that's it. With the correct amount of speed it will stop the object from
>> rotating. Where did the angular momentum go?
> 
>   I thought about this and became to a conclusion. You could have explained
> it if you knew it instead of just saying "you are wrong" without any
> explanation.
> 
>   The answer is that the object-projectile system still has the angular
> momentum. If we calculate the angular momentum of this system after the
> firing, ie. the how the system is oriented with regard to the center of
> mass of the system and the distance between the two objects, we will
> probably get an angular momentum equivalent to the original one.
> 
>   The same is probably true for two approaching objects which collide.
> Even though each object by itself didn't have any angular momentum, the
> two-object system did. The entire two-object system is actually rotating
> around the center of mass of the two objects (even though they two objects
> are travelling almost rectilinearly; this is because they are not travelling
> along the same line in space). When they collide and stick to each other,
> the "speed of rotation" they had just before they collided will be kept. The
> angular momentum will be unmodified. Only if the two objects were travelling
> exactly on the same line in space will there be no rotation because there's
> no angular momentum.
> 
Several times, as carefully as I could I explained that angular momentum 
is conserved in a closed system.  That is a general principle that is 
apparently fundamental to the way the universe works.  Apart from 
stating the principle which you will find in any physics textbook that 
touches on the subject and on many websites, I also explained as 
carefully as I could in this medium where the angular momentum was 
transferred from and to in several examples.

Sorry but you continued to assert that friction could cancel out angular 
momentum and that a spinning closed system could be brought to rest 
without any external force.

When I asked plainly is angular momentum conserved in a closed system 
you replied:

 >>Angular momentum can be lost by converting it to heat (or other forms
 >>of energy for that matter), so the answer is no, unless you don't 
 >>consider it a "closed system" anymore if there's heat dissipation 
 >>(OTOH, this heat could theoretically be collected and stored, keeping 
 >>the whole thing a closed system).

I'm still unclear from your other posts as to whether you still maintain 
this position.  Perhaps you have taken some time to research the facts 
and would recant your statement?

I'll admit to being a poor instructor.  I think you have to admit to 
being a) wrong and b) pig-headed about it.

I will reply to your other posts to try to clear up some of the wrong 
assertions that you continue to make in them.  It would be nice if you 
could reply in one coherent go though rather than in dribs and drabs of 
silliness.

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Warp wrote:
> Paul Fuller <pgf### [at] optusnetcomau> wrote:
>> Sorry but you are just wrong.
> 
>   It's easy to say "you are just wrong" without actually explaining why.
I actually do explain more after that one line that you quoted.
> 
>> In this case you assert that there is a point at which the cables can be 
>> attached that will prevent the stopping action from imparting any spin 
>> to the parent body.
> 
>   Attach the cable to the opposite side of the parent body. What happens?
When the cable goes taut the projectile will exert a force on the body 
(and vice versa) that will be off centre and will cancel the rotation. 
Of course things will bump around but once that is finished the net 
rotation will be as before the projectile was fired.  At every stage if 
you care to add up the angular momentum of the system it will be constant.

I can't reply with numbers and formulae unless you can give a diagram 
with distances, masses and velocities.
> 
>   Besides, we can just forget the cable: Simply shoot the projectile and
> that's it. With the correct amount of speed it will stop the object from
> rotating. Where did the angular momentum go?
It is carried in the off centre velocity of the mass of the projectile.
> 
>> No system of cables, pulleys, magnets, gyroscopes, friction, 
>> electricity, radiation, carbon nonotubes, superconductors or whatever 
>> can alter that.
> 
>   Since a spinning object can be used to produce energy (eg. by friction)
> you are effectively saying that a spinning object is an infinite source
> of energy because its angular momentum will never disappear.
> 
Absolutely not and it is revealing that you misunderstand or 
misrepresent the argument to that degree.  I'm not talking about the 
rotation of any single part of the system being constant.  I'm talking 
about the sum of the angular momentum of the whole system.

As the rotation of a mass A is reduced, an opposite change in angular 
momentum occurs somewhere else in the system.  And not by magic.  simply 
ask what is exerting the tangential force to slow down A and you'll find 
an equal and opposite force acting on that other thing.  And please 
don't say friction is exerting the force!  Some other part of the system 
must be applying the force be it via friction or any other means.

That you make just nonsense statements on my behalf then tear them down 
is poor style.

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Warp wrote:
> Paul Fuller <pgf### [at] optusnetcomau> wrote:
>>>   In order for the rotating secondary object to affect the primary object's
>>> rotation, it has to be connected to the primary object somehow. This
>>> connection causes friction.
>> It has to exert a force and I agree that some energy will be lost in any 
>> practical system.  You are just not getting the point that friction 
>> itself has nothing to do with angular momentum.
> 
>   So you are effectively saying that regardless of heat produced by
> friction, angular momentum is always conserved. This would effectively
> make a spinning object an infinite source of energy.
I am saying that angular momentum is conserved.  As I have replied 
elsewhere to you this does not make your tacked on sentence about 
infinite energy true.  I am not saying that but you have added it 
because you misunderstand or want to misrepresent what I am saying.
> 
>>>   This would be true in a completely friction-free system. The thing is,
>>> friction dissipates part of this energy.
>> Still hung up on friction !
> 
>   A spinning object can be used to produce heat by friction.
Yes.  So can rubbing sticks together.  Neither will in any case alter 
the total angular momentum of a system.
> 
>> True enough.  Friction is the mechanism that takes energy from the 
>> spinning Earth.
> 
>   Where does this energy come from?
There is a spinning mass.  That stores energy in kinetic form.  Slowing 
it down by friction converts stored kinetic energy to heat energy.  It 
does not convert angular momentum into heat.  There will be an effect 
elsewhere that causes a matching change to the angular momentum of 
another part of the system.  Look I even said that in the next paragraph.
|
V
> 
>>  At the same time there is a change elsewhere in the 
>> system that conserves angular momentum overall.
> 
>   Which means that the energy was produced completely for free?
> Isn't that kind of the definition of a perpetual motion machine?
No it is transferred.  Please stop making silly assertions on my behalf.
> 
>> The tidal locking effect is well known and you have described it 
>> reasonably well.  However you are wrong to say that angular momentum is 
>> converted to heat by friction.
> 
>   Then what is it that is converted to heat by friction?
Energy stored in the rotation of the Earth, Moon and both around each 
other.  Lots of energy there!  And if you care to read on the subject 
you'll find that the rotation of the Earth has slowed and the separation 
of the Earth and Moon has increased over time.  The energy has been 
transferred into heat by friction as you say.
> 
>> Angular momentum is a different thing to energy.  Sorry but there is no 
>> known way to convert one to another.  You can certainly use energy to 
>> start one mass spinning.  Thing is that there must be an opposite amount 
>> of angular momentum showing up somewhere else.
> 
>   Two objects with no angular momentum at all collide off-center, and
> they get stuck to each other. The resulting union of masses will start
> spinning because of the collision.
As I think you have realised elsewhere the system comprising the 
original two masses does already have angular momentum.  This then shows 
up as the rotation of the combined body.
> 
>   Somewhere else in the universe something else starts spinning in the
> opposite direction due to a magical universal conservation of angular
> momentum law.
> 
>   Yes, I understand perfectly now. Thanks for clearing that up.
> 
No.  You are just being silly again trying to paint my arguments and 
make them appear ridiculous.  There is no magic and something 
unconnected does not start spinning.  Any change to the rotation of one 
part of a system must be caused by a force exerted on it by another 
part.  That is where you will find the corresponding change in rotation 
that balances out the angular momentum.

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Warp wrote:
> Warp <war### [at] tagpovrayorg> wrote:
>>   Besides, we can just forget the cable: Simply shoot the projectile and
>> that's it. With the correct amount of speed it will stop the object from
>> rotating. Where did the angular momentum go?
> 
>   I thought about this and became to a conclusion. You could have explained
> it if you knew it instead of just saying "you are wrong" without any
> explanation.
So now you're saying that *I* don't understand the topic.  Very, very rich.
> 
>   The answer is that the object-projectile system still has the angular
> momentum. If we calculate the angular momentum of this system after the
> firing, ie. the how the system is oriented with regard to the center of
> mass of the system and the distance between the two objects, we will
> probably get an angular momentum equivalent to the original one.
Sounds like you are coming around to the correct view that total angular 
momentum is conserved.
> 
>   The same is probably true for two approaching objects which collide.
> Even though each object by itself didn't have any angular momentum, the
> two-object system did. The entire two-object system is actually rotating
> around the center of mass of the two objects (even though they two objects
> are travelling almost rectilinearly; this is because they are not travelling
> along the same line in space). When they collide and stick to each other,
> the "speed of rotation" they had just before they collided will be kept. The
> angular momentum will be unmodified. Only if the two objects were travelling
> exactly on the same line in space will there be no rotation because there's
> no angular momentum.
> 
Yes.  Angular momentum is conserved.

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