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Date: Thu, 26 Nov 1998 17:12:17 +0000 (GMT)

Subject: Re: [FT] Railgun Goals

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On Wed, 25 Nov 1998, Thomas Barclay wrote:
> Thomas spake thusly upon matters weighty:
> > this may play well, but as physics it is pretty groundless.
> I'm skeptical about some of the math on the way here.
excellent! skepticism is the soul of rationality. or something. perhaps
the spleen.
> In truth, if your target envelope is a sphere, and your railgun burst
> through it has a spherical cross section (an approximation of sorts),
> is seems likely the burst will generate a truncated-tip conical path
> volume through the volume of space we call the target envelope. The
> ratio of the volume of this conical path to the total size of the
> target envelope volume may be something that defines the hit-miss
> result. It isn't that obvious though, because it isn't strictly a
> relation of these two volumes.
> But your intial work seems to assume
> no spread.
one of those unwritten assumptions, i'm afraid. at extreme range, the
spread will not be very much.
> > i don't see why massdrivers should be smaller than beam batteries;
if
> > anything, i would say they are larger but cheaper.
>
> Depends on relative energy requirements. Which I can't begin to
> caculate...
[rolls up sleeves] old hat; relativity is vital in fudging physics
experiment results!
E kinetic energy
m mass
M rest mass
v speed
c speed of light
k relativistic coefficient
E = mvv/2
m = M/k
k = (1 - vv/cc) ^ 1/2
E = mvv/2
= Mvv/2k
= Mvv/2((1 - vv/cc) ^ 1/2)
for a projectile travelling at half lightspeed (1.5 e 8 m.s), the
kinetic
energy is 13e5 joules per kilogram (if i have done the algebra and
arithmetic correctly, which, given past form, is unlikely).
Tom
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