Re: Guard and Driver - time difference


"Dirk Van de moortel" <dirkvandemoortel@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:_caye.7980$XS1.223@xxxxxxxxxxxxxxxxxxx
>
> "thomaswp" <william-powlettt763@xxxxxxxxxxxxxx> wrote in message
news:1120469074.587766.305790@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > I am a physics teacher. I need to teach relativity to my 17 year olds
> > next term and have been reading the Russel Stannard/Uncle Albert series
> > of books to get some ideas.
> >
> > Now, nothing has surprised me apart from one thing, I hope I can
> > explain it.
> >
> > I understand that in a tall building a clock on the top will run
> > "faster" than a clock at the bottom because the one at the bottom is in
> > a stronger gravitational field, hence spacetime is curved more.
> >
> > But Stannard says that this effect would also be seen in a rocket
> > accelerating fast - namely that a clock at the front of the spacecraft
> > would run faster than a clock at the rear (and that the driver of a
> > train's clock would run slower than the guards at the back of the
> > train).
> >
> > I am confused by the spaceship one - surely in the spacecraft, both
> > clocks are experiencing the *same* acceleration and therefore are
> > synchronised, although to an observer standing between them they would
> > *appear* to be running faster and slower because of red/blue shift.
> > In a train, the frount carriage does not accelerate slower than the
> > back carriage!
>
> If the front and back part of the spacecraft are to experience the
> same proper (felt) acceleration, then the spacecraft will be ripped
> apart after a while.
> See problem 25 pages X-51 and X-69 of
> <http://www.courses.fas.harvard.edu/~phys16/Textbook/ch10.pdf>
> So you want to work with a scheme called "Born rigid motion"
> where the length of the spacecraft will remain unchanged in its
> own frame. Only then will you have a situation that is "equivalent"
> with the tower on Earth.
> See section 13.3.2 pages XIII-6 and problems 5 and 6 of
> <http://www.courses.fas.harvard.edu/~phys16/Textbook/ch13.pdf>
> See also
> <http://www.mathpages.com/home/kmath422/kmath422.htm>
> <http://www.mathpages.com/home/kmath456/kmath456.htm>
> And
> http://groups-beta.google.com/group/sci.physics.relativity/msg/81a14233c7185dc5
> http://groups-beta.google.com/group/sci.physics.relativity/msg/acbd748eda592e27
> and etcera...
>
> Anyway, in both cases the clocks at the front and and the end will
> not remain synchronized.
>
> Perhaps it's not a good idea to talk about accelerated motion
> to 17 year olds. Apart from yourself, you might confuse them
> as well, and turn them into crackpots. as you can see, this
> place is full of people like that.

As you can see from the above, the relativity of accelerating
objects and reference frames is much more complicated than
of inertial objects and frames.

You need to study relativity in inertial frames before venturing
into accelerating frames.

Ignore all the other replies, as Dirk has said, this group is full
of crackpots.

Martin Hogbin



.

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