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From: ables@mcc-db.UUCP (King Ables)
Newsgroups: net.space
Subject: Re: Speed Of Light
Message-ID: <184@mcc-db.UUCP>
Date: Thu, 9-May-85 15:25:10 EDT
Article-I.D.: mcc-db.184
Posted: Thu May  9 15:25:10 1985
Date-Received: Sat, 11-May-85 08:24:46 EDT
References: <2073@decwrl.UUCP>
Organization: MCC (Austin, TX)
Lines: 22

The thing you're missing here is that as you begin dealing with speeds
which are significant next to the speed of light, you can't add
them linearly (actually, you can't *really* add ANY velocities linearly).
If you throw a ball ahead of you at 10 mph from a car going 30 mph, we
say the ball has a velocity of 40mph relative to the stop sign you
just ran ( :-) ).  However, that's not *exactly* true.  It's VERY nearly
40mph, but speeds do not add linearly.  It's just that when you're
this far from the speed of light, they add extremely close to linearly.
As you get up to .5C, you begin to see things like (this is an
approximation) .5C +.5C = .75C.  There is a formula (which I cannot
remember right now, unfortunately) which shows how to calculate
vt = v1 + v2 and it has v/C worked into it somewhere.  For velocities near
0.0, v/C is so small that it isn't significant, but as v gets significant
next to C, the v/C value begins to have an effect on vt.

If I can find the formula at home, I'll post it tomorrow, otherwise, I'm
sure someone else knows it and will post it (they may beat me to it, anyway).
Hope this helps.

-King
ARPA: ables@mcc
UUCP: {ihnp4,seismo,ctvax}!ut-sally!mcc-db!ables