At 08:55 PM 11/6/2009, [email protected] wrote:
In reply to Kyle Mcallister's message of Wed, 4 Nov 2009 18:01:47
-0800 (PST):
Hi,
[snip]
>Any experiment report indicating that the
> thing's thrust is different in different directions, or varies
depending on some (possibly absolute) velocity is very interesting.
[snip]
I think the original author's intent was this (though I didn't study
it properly
and may have completely misunderstood):-
The drive consumes energy at a constant rate, because we supply energy at a
constant rate.
Who (and where) is "we"? I hate to be a stickler, but it's important
here to become very precise. Where is the energy coming from? It
makes a difference. It looks to me like the emdrive trick is a result
of mixing frames of reference.
Part of that energy goes into heating the device, and part goes
into propelling the vehicle.
Heat is the kinetic energy of individual particles or photons.
Kinetic energy requires a frame of reference. What's the frame? If it
is the "craft," which is where the energy conversion is taking place,
and there is no interaction ("reactionless") or emission of energy
(the same) then there is no kinetic energy at all, unless it is
entirely internal, i.e., heat or rotary inertia or oscillatory
inertia, or other contained forms of kinetic energy. Inside the "black box."
It's a bit depressing to see the arguments defending the emdrive. As
I've said, if someone has developed a method of reactionless force,
which is what the emdrive claim is, boiled down, and has demonstrated
it, there would be enormous implications to basic physics, and,
indeed, conservation of momentum is violated. Just take two
snapshots: the situation before the emdrive is turned on, and the
situation after it is turned off. Conservation of momentum is with
respect to a particular non-accelerated frame of reference, and with
respect to any contained system, any "black box" that is not
absorbing or radiating anything, or where the radiation is balanced.
Soppose we arrange the emdrive and power source a faraday cage inside
a sphere, such that the temperature of the sphere is uniform (done
with heat-sinking and radiation inside the sphere), and the sphere is
of uniform material. Likewise the environment is arranged to be
uniform in radiation pressure against all sides of the emdrive sphere.
This is all done in free fall in deep space, so that gravitational
fields are uniform. So the emdrive-sphere starts in the center of our
experimental space, no connections or contacts or interactions between them.
In our frame of reference, the experimental space, the net momentum
of the emdrive sphere begins at zero. The emdrive has a timer which
turns it on for a period then shuts it off, and the internal
components settle to zero motion (except for heat). What is the net
momentum of the emdrive sphere? If it is not still zero, then
conservation of momentum has been violated.
Yet Shawyer claims that conservation of momentum is not violated. He
is obviously contradicting his claim of acceleration!
If we assume that the energy that goes into
propelling the vehicle is converted into kinetic energy (of the vehicle), then
the *power* required is the time differential of kinetic energy i.e.
d(1/2*m*v^2)/dt. This is d(1/2*m*v^2)/dv * dv/dt, i.e. m*v*a (where a =
acceleration).
If we assume that pigs are fishes, then we can all breathe water.
Kinetic energy of the vehicle exists in our ("stationary") frame of
reference. If the vehicle accumulates kinetic energy in our frame,
then, sure, this energy must have come from some source, presumably
the power source inside the emdrive system.
Now, imagine a larger black box, it encloses our frame which encloses
the emdrive system. Call our frame the "room," perhaps it's a space
station experimental lab. And there is a hole in the wall of our lab.
And the emdrive shoots out that hole. What happens to the lab? Does
the lab move in the opposite direction? Regardless of internal
mechanism, in the larger frame, we have a object, the lab, which has
ejected a bit of mass. From normal physics, looking at this from the
larger frame, there is now kinetic energy in the emdrive system, is
there kinetic energy in the lab system?
Conservation of momentum would say, yes, and they balance. Net
momentum is zero. However, if the emdrive is reactionless, there is
no kinetic energy imparted to the lab system. So there is net kinetic
energy. No recoil. No equal and opposite reaction.
Now since the power input is constant, m*v*a should also be constant, which
means that as velocity increases, "a" decreases (assuming constant mass).
In F = ma, there is an assumed frame of reference. And it is assumed
that a force is acting on more than one body, there is no such thing
as a reactionless force in Newtonian mechanics, nor in any mechanics
as far as I know. "Force" means one body or system acting upon
another." A system can't push itself, and, to my knowledge, no
exception is known at any scale. He's claiming an exception, based on
some very shaky math and a very shaky experiment, with very little
detail provided and, given the length of time involved, very little
publication and no independent confirmation of even his small
reported effect. And the experimenter is a microwave engineer who
would not necessarily have any expertise in or experience with
calculating radiation pressure.
Consider this: in the waveguide, microwave energy is being reflected
back and forth. There will be pressure against the walls of the
guide, all the walls. normally, the pressure inside a cavity will be
equal, unless there is an outside force acting (such as gravity,
which would increase the pressure at the bottom and decrease it at
the top, generating a force equal to that of gravity on the contents.)
He claims that the pressure on the sides of the waveguide or cavity
can be neglected. Now, look at a photon, and let's suppose Q is
infinite, the walls of the cavity are perfect reflectors. Now
consider a microwave photon, it has momentum. It is reflected from
the side, a glancing blow (i.e., low-angle reflection). This will
create a force on the side. If the side is oriented in the direction
of the photons, this pressure would be minimal, but that would imply
that the cavity is the same size at both ends (assuming the ends are
parallel planes). Shawyer seems to assume constant radiation pressure
per unit area, but neglects the sides, so, of course, he ends up with
a net force in the direction of the larger area. In fact, if somehow
"friction" with the sides were avoided, if the waves or photons could
be conducted with no pressure on the sides, the pressure per unit
area on the smaller end cap would increase. Such that there is no net force.
More likely, there is some of both effects taking place; there is
pressure on the sides, and so there is a force acting on the sides
that partially balances out the force acting on the large top endcap,
and there is increase of pressure on the smaller endcap; my guess is
that the latter could be a small effect. If I imagine water waves,
focusing the wave on a small area could increase the pressure, indeed.
There are many possible explanations for some force to be detected in
Shawyer's demonstrated; any time you have a large mass and lots of
power, relatively subtle effects that might ordinarily be disregarded
or considered negligilbe, can be seen if you start to make very
subtle measurements. Dean drive. The effect of vibration on
scales.... Heat and effects on air....
If "a" decreases with velocity, then so does the thrust. Note that
relativity is
not taken into account here. All of this is true even at low speeds.
Essentially all they are saying is that at constant power input, the
incremental
change in velocity decreases as you go faster.
Now look at it from the emdrive system. There is no "velocity." While
the emdrive is on, if it's working, there is acceleration,
experienced as equivalent to gravity, right? An accelerometer will
measure this acceleration. Because there is no interaction between
the emdrive system and the outside frame of reference, and because we
can see the outside frame accelerating, we know the relationship
between the acceleration we experience and the apparent motion of the
external world.
But, with the emdrive operating, does the acceleration we experience
(which is precisely equivalent to the "force" acting on our emdrive
system) decline with velocity? If so, we now have a means of
detecting absolute motion.
Now, the energy poured into the cavity is allegedly converted to heat
and to kinetic energy. But from out local, alledgedly accelerated
frame, the is no kinetic energy. We can, however, assume that the
heat deficit is being transferred to our kinetic energy of motion,
but that assumes an external frame. With constant energy input, do we
observe a difference in the emdrive operation based on our velocity
in the external frame? Do we start out with maximum heat deficit and,
as we approach c, the heat deficit declines, i.e., more of the
generated energy is converted to heat.
No, I think, what was said above was that the energy input was
constant, and the loss of acceleration was due to the fact that
kinetic energy varies with the square of the velocity. Frames of
reference are being totally mixed. The velocity of the emdrive in the
external frame cannot affect the force of acceleration experienced by
the occupants of the emdrive frame, or else there is an absolute
external frame of reference, i.e., absolute velocity. Shawyer's
emdrive theory claims to satisfy conservation of momentum and the
theory of relativity, but, in fact, blatantly contradicts them.
That some here think that relativity isn't valid doesn't affect this.
Maybe it's not valid. But that doesn't make Shawyer's work valid, at
all. He has a bogus theory, and that's been largely acknowledged
here. If he has a bogus theory that he's working hard to prove, he's
quite likely to come up with small evidences. That's what people are
good at doing, finding facts that confirm what they believe. He's not
finding facts on a scale, however, that would be likely to convince
anyone who knows basic physics, and the real key, to me, to this
situation is that he's claiming compliance with physics, providing
hand-waving and clearly bogus explanations.
If he was claiming, "I've discovered this anomaly, and I don't know
why it's working, but it is," then I'd not at all be convinced of the
probable fraudulent nature of his work. His explanations are so
transparently hand-waving, however, that it's become, for me, very
difficult to believe that he doesn't know exactly what he's doing.
