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.

Post a reply to this message