mix...@bigpond.com wrote: > In reply to Stephen A. Lawrence's message of Sat, 28 Mar 2009 17:11:47 -0400: > Hi, > [snip] >> But inertial propulsion systems proposed here don't work with parts >> moving at relativistic speeds -- or at any rate nothing I've seen >> mentioned recently in this group did. But maybe I'm just confused about >> this. >> > All speeds are relativistic. The relativistic effect is the origin of kinetic > energy.
Ah, c'mon, you know what I mean.... "Relativistic speeds" are such that the terms which are second order in the velocity start to matter. To first order in (v/c)^2, gamma = 1/sqrt(1-(v/c)^2) ~ 1 + (1/2)(v/c)^2 and as long as v << c you can ignore the (v/c)^2 term and get answers which are accurate to within the errors in your measurements. When speeds are "relativistic" you can't ignore the (v/c)^2 term anymore, or risk getting results which are outside your error bars. And as long as we can ignore the terms in (v/c)^2 then the kinetic energy is close enough to (1/2)mv^2 that we can take that as exact. IOW it's only when v gets to a significant fraction of a percent of c that Newton's laws start to look blurred. Certainly, to pick one example (made purely of straw), the Dean drive didn't move anything nearly fast enough to qualify for the need for a relativistic correction. In general, anything made of macroscopic mechanical parts which you can actually operate in a laboratory is going to be operating in the domain where Newton's laws are (apparently) exact. > > Regards, > > Robin van Spaandonk > > http://rvanspaa.freehostia.com/Project.html > >
