Re: FLOW of energy

[William Beaty <billb@eskimo.com>]

On Mon, 1 Sep 1997, Jim Green wrote:

> But remember the problem which initiated this thread (this time) -- the
> block sliding on a "big" plate.  The tread was reduced to cacophony and as
> far as I can see a solution was never agreed to -- mostly I think because
> the language used was foggy and had stuff "flowing" -- all sorts of
> weirdness was introduced -- including "pseudo-work", etc.

How about a simpler situation.  Well, maybe not simpler, but one which
eliminates some hidden features and shines light on everything.

Eliminate gravity and don't concentrate too hard on one inertial frame.

I'm floating in space.  I have two very long rods lying parallel.  I grab
the two rods with my hands.  A block is attached to the far end of one
rod.  A plate is attached to the far end of the other.  A force is holding
the surfaces of the block and plate in contact.  (Perhaps a massless
rubber band binds them together, perhaps they are insulating materials
having opposite charge, I don't care.)

If I suddenly jerk the rods, pulling one rod and pushing the other, my
ends of the rods immediately move in response.  The rods are long, so the
propagation of pressure waves takes percievable time.  A positive wave
"flows" along one rod, a negative waves "flows" along the other.  When
these waves arrive at the far end, they cause the block to move in one
direction, while the plate moves in the other.  For convenience, lets say
that the mechanical propagation impedance of the rods matches that of the
block/plate system so that no wave reflections are created.  The block and
plate slide against each other, nano-mechanical and chemical bond
stick/slip processes occur on their surfaces which "twang" the electrons
in the surface atoms.  On the macro scale, this "friction" slows the
movements of the rods and absorbs the propagating wave.  The wave travels
into the plate and block, and is absorbed by the sliding surfaces.  Those
surface electrons broadcast high frequency acoustic and em vibrations into
the bulk of the plate and block.  Finally everything is still again.  The
temperature of the block and plate are higher than they were initially.
Some chemical fuel in my muscles has changed state.

I performed work upon the ends of the rods.  It seems (at least to me) 
that this "work" or "mechanical energy" or "acoustic energy" propagated or
"flowed" along the rods and through the bulk of the plate and block, and
was finally absorbed and converted into something else by the sliding
surfaces.  The sliding surfaces acted as a mechanical resistor, as a
transmission-line terminating impedance.  They did this in about the same
nonlinear way as a hair comb converts linear motion of a fingernail into
oscillating motion of many comb-tines.

If my entire thought-experiment is morphed to become a person who pushes a
book across a table, nothing fundamental changes.  Now, what's left to
misunderstand?  Work can flow.  Nonlinear processes can convert linear
relative motion into micro-scale atomic oscillations.  "Performing work" 
can become "broadcasting sound", which can become "heating objects."  The
physics of transmission lines is in there, as well as simple Newtonian
dynamics.

......................uuuu / oo \ uuuu........,.............................
William Beaty  voice:206-781-3320   bbs:206-789-0775    cserv:71241,3623
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