Re: Summarry of the momentum wars and idea.

[KellySt@aol.com]

to:  stevev@efn.org

 > > If a static structure had to dissipate energy continuously to
 > > remain standing, where would such energy come from?  Why doesn't
 > > your house fall down?  Where are the batteries?
 > 
 > The energy is coming from the gravitational attraction of the earth.  It
is
 > disapated as heat in the structure of the house.  In a structure under
heavy
 > loads (too heavy) you can feel the heat in the structure.

Steve>> Really?  So when does the earth run out of gravity?

When space gets tired of curving?  ;)

Steve>> I think you've spent too much time in the Cartoon 
Steve>> Physics section of Acme Physics Warehouse.

Steve>> Tell me about one of these structures that I can go
Steve>>  visit, put my hand on, and feel the heat.

Over stressed cable stayed structures are about the only ones I've delt with
that I could feel the differnce in.  Others are too low to feel, but
insterments can detect it.


========================================================
:  stevev@efn.org

KellySt@aol.com writes:
 > >> Besides not treating momentum as a vector quantity, people are
 > >> making the mistake of thinking that lateral loading of the sail
 > >> assembly is a magical sink for momentum or energy.  The error is
 > >> in thinking that stress on a static structure absorbs energy or
 > >> momentum continuously over time.  If the sail does not move
 > >> relative to the ship, then it cannot absorb or dissipate momentum
 > >> separately from the ship.  It cannot absorb momentum if it does
 > >> not move, because momentum means motion.  ----
 > 
 > (??!)  <sigh>
 > Thats like the old argument that if a tractor is pushing against a wall
its
 > doing no work, since the wall isn't accelerated.  The sail is getting a
 > thrust that is perpendicular to the surface of reflection.  If you want to
 > describe the portion of the thrust that isn't accelerating the ship as
 > invalid, enjoy.

S >> The tractor is dissipating energy because it contains 
S >> moving parts in its engine and drive train that keep 
S >> moving even though the tractor chassis and the wall 
S >> are not.  

Now whos trying to talk their way out of a corner.  Try a direct drive
electric tractor.  Nothing turns unless the vehical moves.  So where does the
power go if nothing moves?

--

S >>  Lean a board against the wall.  Does it dissipate energy 
S >> because it can't move the wall?  Lean a heavy iron bar 
S >> against the wall.  Does it dissipate more energy than 
S >> the board?  

They are under a constant 1 g thrust.  They are under the load resisting that
takes.  Where do you think that power goes?

S >> Are the bricks at the bottom of the wall permanently 
S >> warmer than the bricks at the top because they are under 
S >> compression?

Yes.


S >> ---  You can't claim that gravity is continuously pumping
S >>  energy into the objects; you can't gain or lose energy if 
S >> you don't move up or down in a gravity field.

If non-moving structures are not continuously being subjected to a force,
what keeps them under continuous presure?  Something is crushing their
molecular structures enough to put them under a load.  If that presure was
removed, or droped, they would expand.  In the same way the structure in the
sail bracing is under continuous stress.


S >> My intention was to prove that Kevin's parasail design 
S >> couldn't absorb photons without absorbing their 
S >> momentum.  

But you can divert the thrust vectors to a non-forward direction. in a
reflection.  Its not going to buy you anything is you later absorb the
photons anyway, but it is a usefull trick to move the beam around without
geting shoved by it.  (Frankly with all the bouncing, have defined equations
getting tossed around I'm not sure if that was Kevins point anymore.) 


s >> You seem to have a real misunderstanding of the 
s >> difference between work and potential.  When you put a
s >>  structure under tension or compression, you do change 
s >> its energy, ONCE, when you slightly pull apart or scrunch 
s >> together 

Actually, I'm probably not being as clear as I might be.  However, the
differnce if fairly accademic as far as the ships concerned.

 > One very consistent problem in LIT over the last year has been
 > a very limited interest in the engineering realities of a
 > situation, and to much fondness for endless equation wars.


s >> These are not equation wars; as this message shows, you
s >>  don't always have to use math to talk about physics.  

But in the Equation wars, no one was using anything but equations (usually
not well explained or defined).  This not only caused confusion to everyone
else, it frequently tripped up the person making the statment

Kelly