Re: Summarry of the momentum wars and idea.

[Steve VanDevender <stevev@efn.org>]

KellySt@aol.com writes:
 > 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?  ;)

So what you are saying is that any gravitational source is a
supply of infinite energy.  All one need do is hang a weight from
a wire or stack up a bunch of bricks, attach a thermocouple to
the now warmer structure, and get free electricity, forever.

This is such an amazingly simple principle that I am surprised
such a method pf power generation has not been tapped already.
Who needs sunlight to evaporate water to fall as rain to flow
through rivers to run hydroelectric generators, when one could
use a farm of gravitationally stretched or compressed objects and
a heat exchanger to run a boiler to make steam to run the
generators instead?

The curvature of space also carries energy, but a finite amount.
Objects in a gravitational field can't dissipate heat forever;
the energy has to come from somewhere, and there is no such thing
as an infinite inexhaustible supply of energy in the universe.

 > 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.

Are these structures under true static stress?  Is the heat
coming from an overstressed, gradually elongating cable (in which
case work is being done on the cable material), or can you set up
such a structure and get heat from it forever without
degeneration of the structure?  If so, how do you explain getting
more heat from the structure than you put energy into it when you
built it?  If such a structure could persist indefinitely, how do
you explain where the energy came from when the structure has
been around long enough that the total dissipated energy exceeds
the energy equivalent of the mass of the structure and the
gravitational source?

 > 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?

If an electric motor is prevented from turning then the energy
that is not producing motion heats the motor windings; if the
motor does not turn then the windings are an electrical short
circuit.

An ideal electric motor draws no power if it does no work.  As
you should know as a student of engineering, ideal motors are as
common as unbending beams.  Any real motor has resistive and
mechanical losses that will cause it to draw power even if it
does no work.

I can keep this up for a long time, because I know what I'm
talking about.  You are making claims that would get you a lot of
stern looks from your physics professor, if not outright
laughter.

 > 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?

There is no power dissipation, because there is no motion.  Power
isn't going anywhere.

Power is work over time.  Work is force times distance.  A force
that is prevented from producing motion produces no work; no work
over any amount of time is no power.

You have equated work (or energy) with force, a mistake that
should have been corrected in your first class that covered
Newtonian physics.

 > 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.

You need to have a long, long talk with a physics professor.

 > 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.

That stress requires extension in space.  It is true that moving
up and down in a gravity field changes the energy of the object.
But if no motion occurs, there is no change in energy.  The
compression of the structure occurred once and added a finite
amount of energy to it.  There is no continuous dissipation of
energy as you seem to think; the bricks at the bottom of the wall
got warmer just after the other bricks were stacked on top of
them, but do not stay warmer forever, because no more work is
done on them.  No motion through the gravity field means no work;
no work is no energy.

 > 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.) 

You can reflect different parts of the beam in different
directions to produce sideways components of momentum that cancel
over the entire structure.  You cannot take forward momentum and
turn it into sideways momentum without giving the forward
momentum completely to something else.  When I say that momentum
is a vector quantity and is conserved as a vector quantity, what
I mean is that if you have a quantity of momentum, its direction
is as important as its magnitude, and although you can divide the
momentum up however you like, even split zero components into
complementary non-zero components aimed in opposite directions,
the sum of all the momenta of all the things you divide it up
among sums to momentum in the same direction with the same
magnitude.

The ship gets all of the forward momentum of each photon it
absorbs, no matter how the photon was reflected or redirected
before the ship finally absorbed it.  There is no other way to
satisfy conservation of momentum.

 > 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.

Frankly, your understanding of physics would get you marked as a
raving loon.

 >  > 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

How much math have I used to explain conservation of energy and
momentum here?  I think I have a clear and accurate understanding
of those concepts, which does not lead me to the contradictory
conclusions you are coming up with.  Your claims quite clearly
imply that you can get indefinite amounts of heat energy from an
unmoving structure in a gravitational field, because you say a
structure in a gravitational field is warmer and stays warmer
than an equivalent structure not in a gravitational field.  You
cannot claim to be playing by the same rules of physics that the
rest of us are trying to play by.  Your knowledge of physics has
flaws and gaps that I have already spent too much time trying to
correct and fill.