Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Shawyer's EMdrive

  1. Sep 11, 2006 #1
    http://www.shelleys.demon.co.uk/fdec02em.htm" [Broken]
    And check out new scientist's issue last week if you have subscription, http://www.newscientist.com/data/images/archive/2568/25681401.jpg" [Broken]

    What do you guys think of the science behind this? He says with a superconducting cavity he could get 30,000 newtons per kilowatt - enough to lift(hover) a large car.

    He says it wouldn't be useful for propulsion but if it can lift a car againts gravity for a long period of time.. remove that gravity (such as in space) would it not go flying? And would it not be able to achieve at least 1g acceleration? (ie eath-to mars(median 280mil km) in just under 4 days including turnaround)

    Thanks, (whats my nick again?):confused:

    P.S btw sry if this has been posted before, I searched.. nothing .. im new..
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Sep 20, 2006 #2
    It seems to violate conservation of momentum, but I'm a bit rusty as to taking into account the momentum contained in the EM field. Also, I don't think the radiation pressure on one side of the cavity would be smaller than the other since the effective areas are the same once you take into account the sloped inner surface.
  4. Sep 20, 2006 #3


    User Avatar

    Staff: Mentor

    From the diagram, it is pretty simple to understand why it doesn't work: radiation pressure is what he's talking about and pressure is force over area. The pressure on one side would be higher than the other, but the net force is the same in both directions.

    In the photo of his demonstration device, I notice there is something sitting under the side of the balance that his device is sitting on...
    Last edited: Sep 20, 2006
  5. Dec 21, 2008 #4
    What does Lorentz Force have to do with this machine? In his paper, he uses a shortened version for the force which neglects the cross-product between velocity and the magnetic field. In Shawyer's formulation the force is just placed there without regard for the direction.
  6. Dec 22, 2008 #5

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    By all appearances, this is a crank claim and not worth discussing. The paper has never been published in a peer-reviewed journal.

    This thread should have been locked long ago.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook