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Relativity anyone? - RF Cafe Forums
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Jorrie
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Post subject: Relativity anyone?
Posted: Thu Jun 15, 2006 1:53 pm
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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If speeds in space one day get up to a significant
fraction of the speed of light, will the usual Doppler
radar solution: fractional frequency shift = twice
the relative speed (expressed as a fraction of the
speed of light) between the radar and the target
still hold? Stated differently: is (Delta lambda)/lambda
= 2v/c still valid?
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Jorrie |
Post subject: How about twin paradox?
Posted: Sun Jun 18, 2006 11:49 am
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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Since there was no response to the Doppler question,
how about the twin paradox? Do you believe the story
that if one twin sets out on a long, very fast return
trip, he/she will end up younger than the stay-home
twin?
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Kirt Blattenberger
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Post subject:
Posted: Mon Jun 19, 2006 8:14 am
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Site Admin |
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Joined: Sun Aug 03, 2003
2:02 pm Posts: 451 Location: Erie, PA
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Greetings Jorrie:
It is not really a question
of belief. Many experiments have been carried out
using atomic clocks in aircraft, as wellas in space
vehicles, that confirms absolutely the tenets of
general relativity. As an example, the effects of
both lower gravitation and relative speed are corrected
for in the GPS system. A Google Search on the topic
will yield a plethora of information on the topic.
Thanks for writing.
_________________ - Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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Jorrie |
Post subject: Converted relativist
Posted: Mon Jun 19, 2006 9:11 am
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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Hi Kirt,
Firstly, thanks for a great site
and forum! Secondly, thanks for replying.
I'm actually a "converted relativist" and made
the statement in my previous post only to try and
extract some reaction! I agree with all that you
said.
By the way, any ideas on my Doppler
radar question? (I know engineers don't need relativity,
but it's still intriguing!)
Jorrie
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nubbage |
Post subject: Relativity Anyone?
Posted: Mon Jun 19, 2006 9:54 am
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General |
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Joined: Fri Feb 17, 2006
12:07 pm Posts: 236 Location: London UK
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I've been idly sucking my thumb over the weekend
thinking of this one, without much result. One
of the thoughts that wafted my way was: if we observe
from earth using a spectrometer the collision betwixt
two very large objects, super-suns (as found in
colliding galaxies), occurring along our line of
vision, one will be receding from us and have a
red shift corresponding to say 60% of the VOL, and
the other approaching it and us with a blue shift
corresponding to 60% of the VOL.
Does that
mean the relative velocity between them is 120%
of the VOL? If not, why not?
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Jorrie |
Post subject: Addition of velocities
Posted: Mon Jun 19, 2006 10:17 am
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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Relativistic velocities measured in the same inertial
frame adds up as v = (v1/c+v2/c)/(1+v1v2/c^2). This
means that if an observer riding with your "super-sun"
A measures the velocity of "super-sun" B, the result
will be 1.2c/1.36 = 0.882c. The reasoning behind
the "relativistic addition of velocities" equation
is rather complex and requires some knowledge of
relativity.
Hope it helps. Jorrie
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Kirt Blattenberger
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Post subject:
Posted: Mon Jun 19, 2006 4:16 pm
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Site Admin |
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Joined: Sun Aug 03, 2003
2:02 pm Posts: 451 Location: Erie, PA
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Greetings Jorrie:
I thought you might be
tweaking us a little in order to provoke a discussion.
The subject of relativistic speed addition brings
to mind the old (well, it can't be too old) Einsteinian
Commandment, "Thou shalt not add thine own speed
directly to the speed of thine fellow traveler."
Since the relativistic addition of velocities
is given by
V = v1+v2/sqrt (1+ (v1·v2/c²)),
it can be seen that when v1 and/or v2 are very
small compared to c, the equation reduces to the
Newtonian form of
V= v1 + v2 QED (always
thought that QED thing looked scholarly).
_________________ - Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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Jorrie |
Post subject: Re: Addition of velocities
Posted: Tue Jun 20, 2006 2:32 am
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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Hi Kirt, a very nice Einstein Commandment!
To stick to it diligently, however, requires
some care with the formula.
The equation
that you gave [V = v1+v2/sqrt (1+ (v1·v2/c²))] 'sins'
heavily. The one that I gave [v = (v1/c+v2/c)/(1+v1v2/c^2)]
'sins' lightly, but sin is sin!
Can anybody
spot the two problems? Hint: relativistic addition
of velocities cannot result in a velocity greater
than c... And watch those units of measure!
Jorrie
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Jorrie |
Post subject: Tying Loose Ends
Posted: Fri Jun 23, 2006 1:23 pm
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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To guard against loose ends in threads, I'm stitching
this one up - the correct relativistic addition
of velocities is: v = (v1+v2)/(1+v1.v2/c^2),
where v, v1, v2 and c are in conventional SI
units of m/s. The 'sin' in my original formula was
units of measure. The r.h.s. implied that v1 and
v2 were SI velocites, while the left hand implied
velocity as a fraction of c, due to the lack of
the division by c (not intended as a test, but a
typo, I must confess). You can read more
on this and other special relativity formulae in
a download from my website
http://www.einsteins-theory-of-relativi ... ement.html
Jorrie
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Kirt Blattenberger
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Post subject:
Posted: Fri Jun 23, 2006 11:34 pm
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Site Admin |
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Joined: Sun Aug 03, 2003
2:02 pm Posts: 451 Location: Erie, PA
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Greetings Jorrie:
I took the occasion of
you posting your great Relativity 4 Engineers website
URL to give you a little extra promotion by listing
your site in the Recent Additions list on the RF
Cafe homepage.
I have always had a big interest
in relativity and used to do quite a bit of reading
on it back when I had more time (that would be about
20 years ago). My own attempt at a Relativity page
is pretty pathetic, but it will be vastly improved
as I go about updating material.
Thanks for
your contributions.
_________________ - Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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Jorrie |
Post subject:
Posted: Sat Jun 24, 2006 3:59 am
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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Hi Kirt
Thanks for the publicity. I was unsure
on the issue of free 'advertising'. Relativity 4
Engineers contains a lot of free content and, as
you perhaps spotted, no advertising other than promoting
the ebook-to-be, which will be sold from another,
more commercial website.
Keep up the good
work! I will post interesting relativity and cosmology
tidbits from time to time.
Regards, Jorrie
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Jorrie |
Post subject:
Posted: Sat Jun 24, 2006 4:02 am
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Joined: Tue Jun 13, 2006
4:22 am Posts: 10 Location: 25.9S 28.1E
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Hi Kirt
(Some hiccup on my side caused a
double post!)
Regards, Jorrie
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Posted 11/12/2012
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