Re: Distance-dependent time contraction

From: mich (mich_at_efni.com)
Date: 06/25/04 

Date: Thu, 24 Jun 2004 22:38:43 -0400

Thanks for your help Dirk; I really appreciate it.If I have some other
problems, I'll let you know.

Andre

"Dirk Van de moortel" <dirkvandemoortel@ThankS-NO-SperM.hotmail.com> wrote
in message news:IIICc.165373$%q1.8157290@phobos.telenet-ops.be...
>
> "mich" <mich@efni.com> wrote in message
news:10dmka6o8pn4215@corp.supernews.com...
> >
> > "Dirk Van de moortel" <dirkvandemoortel@ThankS-NO-SperM.hotmail.com>
wrote
> > in message news:rvxCc.4639$9t2.1064@news.cpqcorp.net...
> > >
> > > "mich" <mich@efni.com> wrote in message
> > news:10dkeib1unj4db4@corp.supernews.com...
> > > >
> > > > "Dirk Van de moortel" <dirkvandemoortel@ThankS-NO-SperM.hotmail.com>
> > wrote
> >
> > > > in message news:u%gBc.161297$Yb2.8243253@phobos.telenet-ops.be...
> > > > >
> > > > > "mich" <mich@efni.com> wrote in message
> > > > news:10db3ut6mqs0g97@corp.supernews.com...
> > > > > >
> > > > > > "Dirk Van de moortel"
<dirkvandemoortel@ThankS-NO-SperM.hotmail.com>
> > > > wrote
> > > > > > in message
news:0gYAc.160388$BL2.8269913@phobos.telenet-ops.be...
> >
> > I went through our posts and I found something that you wrote:
> >
> > ________________________________________________________
> > You wrote
> > Remark:
> > In order to measure lengths you don't actually need rods.
> > You can measure lengths with light and a clock only,
> > using the assumed fact (postulate) that light speed is
> > always the same. Send a signal, wait for the echo, find
> > the time between sending and receiving, and you know
> > how far away (and when) the signal hit the target.
> > To use this system for measuring a moving rod requires
> > two signals and echoes, in such a way that the front and
> > the back of the moving rod are hit by your signals at the
> > same time (time measured by yourself of course!).
> >
> > _______________________________________________
> >
> > The second explanation I wrote seems to match yours, although I may not
have
> > been as clear.
> > _____________________________________________
> >
> > a quote from you:
> >
> > "To use this system for measuring a moving rod requires
> > two signals and echoes, in such a way that the front and
> > the back of the moving rod are hit by your signals at the
> > same time (time measured by yourself of course!)."
> > _________________________________________
> >
> > The reason why I elaborated a little bit is due to the difficulty of
knowing
> > whether the two signals hit the front and back of the moving rod at the
same
> > time.So here's my second explanation again, and I'll wait for your
response.
>
> Very good! You found exactly what you needed to solve it,
> and there really is no need to repeat that explanation.
> You just found it!
>
> Look:
> "To use this system for measuring a moving rod requires
> two signals and echoes, in such a way that the front and
> the back of the moving rod are hit by your signals at the
> same time (time measured by yourself of course!)."
> That's all there is to it.
> You can measure the distances and the times of the reflection
> events on both sides of the rod, so just make sure that both
> times are the same, and then you take the difference of the
> distances of the reflection events, and hey presto!
>
> Recall the definition of "the time of an event" as
> t = (te+ts) / 2
> and distance as
> x = c*(te-ts)/2.
>
> So for the reflection event on the near side of the rod you
> calculate
> t1 = (te1+ts1)/2 and x1 = c*(te1-ts1)/2
> and likewise for the other reflection event on the far side
> t2 = (te2+ts2)/2 and x2 = c*(te2-ts2)/2 .
> So, if you arrange for things such that
> t1 = t2 [ in other words delta(t) = t2-t1 = 0 ],
> then the length of the rod is given by the difference of the
> distances of the near and far side:
> delta(x) = x2 - x1
>
> It works for a moving rod, and for a non-moving rod it works
> just as well of course. It's *that* simple.
> Nice, isn't it?
>
> Dirk Vdm
>
>

Relevant Pages

  • Re: Distance-dependent time contraction
    ... > the back of the moving rod are hit by your signals at the ... You can measure the distances and the times of the reflection ... So for the reflection event on the near side of the rod you ...
    (sci.physics.relativity)
  • Re: Distance-dependent time contraction
    ... To use this system for measuring a moving rod requires ... the back of the moving rod are hit by your signals at the ... The second explanation I wrote seems to match yours, ... >> At the instant I stop receiving the reflected signal, ...
    (sci.physics.relativity)