In reply to Craig Haynie's message of Sun, 10 May 2015 23:43:04 -0400: Hi, >" IOW he creates a force, but as long as that force doesn't act over a >distance, then it need do no work." > >I'm the one who suggests that the thrust created by the EM Drive could be >used to levitate an object. Shawyer is saying that the EM Drive could >create 1 tonne of thrust for 1 kilowatt of power, implying that this thrust >would be used to accelerate a spacecraft. He's not siting these numbers as >an example of levitation. So he's implying that the thrust will be used to >do work, and therefore should not be able to violate a theoretical amount >of power needed to do that work.
...but he isn't stating how much work is done, and hence how much power would be required. He is just saying that his device even at it's most efficient still requires that some power be expended to create a force, even though in theory no power expenditure is required to create a force, see e.g. gravity , or even a simple spring, which will happily create a constant force, without expending any energy. IOW the (in)efficiency of the device is what causes the power requirement. What I am trying to say is that the power requirement that he gives, is for a device doing no work. If it has to do work as well, then the power requirement will increase accordingly. Consider for a moment the ultimate form of the drive, which is constructed from a perfect superconductor with a consequent infinite Q. As the Q increases so does the force. Or looked at from a different perspective, the power requirement to obtain a given force decreases as the Q increases. IOW in a perfect device, the power requirement would approach zero (as long as no additional work need be done). Which is exactly what a spring does. (And also a current in a superconducting loop BTW.) BTW, IIRC (it was some time ago that I read this) he does say somewhere that the power consumption changes as work is done, and that consequently the limits on the input power also limit the amount of work that can be done. Note also that the tests to date, have been done on stationary devices, i.e. anchored to the work bench, so that they could not move (as I understand it), and hence did no work. [snip] Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
