[Phys-L] Re: "moving clock runs slower" (yes)

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

> I was sort of following along until John Mallinckrodt wrote:
>
> >  Both twins determine the time for the trip by dividing the
> >  distance traveled by the relative velocity.  Since the stay
> >  at home twin determines that it is "really" a larger
> >  distance, he finds that the trip "really" takes longer.  Q.E.D.
>
> The time is measured as the distance divided by the relative velocity?
> How do you measure the relative velocity?  Now I'm lost.

There is only one possible relative velocity (perhaps I should have
said "speed" since you can't divide a length by a velocity, but I'll
operate on the assumption that that wasn't the point of
confusion)--that between the reference frame in which the planets and
the "stay at home" twin are at rest and the reference frame in which
the "traveling" twin is at rest.  Either twin can measure it by
determining how fast the other one is moving using, for instance, a
Doppler radar.

John Mallinckrodt
Cal Poly Pomona
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