[Physics] Physics Digest, Vol 19, Issue 5

[carmam at tiscali.co.uk]

Tuffail, read "Relativity The Special And The General Theory" by A Einstein (or your favourite reference book - but I prefer it straight from the horse's mouth), chapter XII, first paragraph. First sentence :- "I place a meter rod in the x' axis of K' in such a manner that one end (the beginning) coincides with the point x' = 0, while the other end (the end of the rod) coincides with the point x' = 1. What is the length of the meter rod relative to the system K?"
This clearly indicates that the rod is positioned radially to the origin (the observer) ie one end is positioned with the observer, and the other end away from him.

"...the values of these two points at the time t = 0 can be shown to bex (beginning of rod) = 0 sqrt( 1 - ( v^2 / c^2 )) x(end of rod) = 1 sqrt( 1 - sqrt( 1 - ( v^2 / c^2 )) the distance between the two points being sqrt( 1 - ( v^2 / c^2 )) " 
All items between quotation marks are a direct quote from the book. His thought experiment with the railway line, the carriage, and lightning strikes also uses only radial velocity. 
I am guilty of simplification in my description of transverse velocity. If the object is in a perfectly circular orbit around the observer, ie the observer is at the centre of the orbit, the radial (relative) velocity is zero. If the object is travelling at right angles to the vertical above the observer, and in a straight line, yes there will be some radial velocity. However, if the object chosen is far enough away, and we choose the observation zone to be limited in length to just a few degrees either side of vertical, the radial velocity will be so minute that it can be ignored.  
Tom.  
----Original Message----
From: tufail.abbas at gmail.com
Date: 01/12/2018 19:43 
To: <carmam at tiscali.co.uk>, "General Physics and Natural Philosophy discussion list"<physics at tuks.nl>
Subj: Re: [Physics] Physics Digest, Vol 19, Issue 5

Tom,
I did not commented on your words, because I don't know what you intend to say. You said 
Einstein's relativity deals with relative motion, which is movement to or from the observer.

I am sorry, but  relative motion does not mean "movement has to be TO OR FROM observer". It can be in any direction provided we are doing correct vector maths.
And then you said "An object with transverse velocity to me has no relative velocity"

Again I have to say that traverse velocity is also a relative velocity, even as per high school level physics,
Perhaps, you mean something else, which I am unable to understand.
Regards,
Tufail Abbas 










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