Re: Please debunk the EmDrive for me

BellT <nonono@xxxxxxxx> wrote:
The short answer:
Newton's third law.

As for "jokers", how about the entire explanation of it.
I think every single sentence has an error. I don't want to elaborate,
because I bet the author of those stories will just cut and paste the
explanations into their story.

But...but...it's the cover story in this week's New Scientist! Could
they be wrong?

From the article:

"Take a standard copper waveguide and close off both ends. Now create
microwaves using a magnetron, a device found in every microwave oven. If
you inject these microwaves into the cavity, the microwaves will bounce
from one end of the cavity to the other. According to the principles
outlined by Maxwell, this will produce a tiny force on the end walls.

....[stuff about tuning the cavity for resonance skipped]...

"You might think the forces on the end walls will cancel each other out,
but Shawyer worked out that with a suitably shaped resonant cavity,
wider at one end than the other, the radiation pressure exerted by the
microwaves at the wide end would be higher than at the narrow one."

Hm, why bother with microwaves? Just fill the tapered cavity with
compressed air, and the force of the air on the big end will indeed be
greater than the force on the small end. This must be the reason that
compressed gas always comes in cylinders. If the ends weren't precisely
the same size, the unbalanced forces exerted by the gas would make the
cylinders whizz off in all directions.

--
Richard Kennaway
.

Relevant Pages

  • Re: Please debunk the EmDrive for me
    ... microwaves using a magnetron, a device found in every microwave oven. ... from one end of the cavity to the other. ... the radiation pressure on both sides ... What about a cone with a large angle, 170 or 179 degrees, still no force on the sides? ...
    (rec.arts.sf.science)
  • Re: Faulty Microwave Oven
    ... >>There may be some truth to this myth, but I've run microwaves without ... > so it all ends up going back into the magnetron. ... is put into the cavity, ... Modern ovens ...
    (sci.electronics.repair)
  • Re: Please debunk the EmDrive for me
    ... microwaves using a magnetron, a device found in every microwave oven. ... from one end of the cavity to the other. ... microwaves at the wide end would be exerted across a wider area than at ... the radiation pressure on both sides ...
    (rec.arts.sf.science)
  • Re: Please debunk the EmDrive for me
    ... Hm, why bother with microwaves? ... Ping-pong balls would work too. ... cavity" to put this thing on the same shelf as the Dean Drive and ...
    (rec.arts.sf.science)
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