Re: Spaceship Question


Henri Wilson wrote:
On Mon, 13 Feb 2006 23:17:49 +0100, "Paul B. Andersen"
<paul.b.andersen@xxxxxxxxxxxxxxxx> wrote:

Henri Wilson wrote:
On Sat, 11 Feb 2006 16:19:02 +0100, "Paul B. Andersen"
<paul.b.andersen@xxxxxxxxxxxxxxxx> wrote:


Yes Paul. You are slowly getting the idea.

Neither the rod nor the tape physically changes with movement. You assured me
that SR agrees with this.


So how do you propose to measure the length of a _moving_ rod, Henri?

Care to try again?
Think practical, Henri.
If you should measure the length of a train passing
by you at 200 km/h (but you don't know the exact speed),
how would you do it?


The easiest way would be to hop on board and pull out your tape again.

A more difficult way would be to place a line of detectors and W-synched clocks
along the track at known spacing and monitor the passage of the train's front
and back ends.

My first suggestion is by far the easiest.

OK, Henri.
I have got the message.
You don't know how to measure the length of a moving train.
You do not have to repeat it any more times now.

Paul, as I explained elsewhere, I would not be so stupid as to try to measure
the length of a train while it was moving. Only an SRian would even consider
such an exercise.

You and Seto and Greenfield share the opinion that measuring the length
of a moving object is impossible, not realizing of course that it's
done routinely.

PD


However if you asked me how I would measure the diameter of a distant galaxy, I
would probably take your question more seriously....the 'tape measure' method
being no longer practical.

Paul


HW.
www.users.bigpond.com/hewn/index.htm

.

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