Re: Spaceship Question
- From: "Paul B. Andersen" <paul.b.andersen@xxxxxxxxxxxxxxxx>
- Date: Mon, 13 Feb 2006 23:17:49 +0100
Henri Wilson wrote:
On Sat, 11 Feb 2006 16:19:02 +0100, "Paul B. Andersen"
<paul.b.andersen@xxxxxxxxxxxxxxxx> wrote:
Henri Wilson wrote:
On Mon, 06 Feb 2006 23:22:57 +0100, "Paul B. Andersen"
<paul.b.andersen@xxxxxxxxxxxxxxxx> wrote:
Henri Wilson wrote:
On Wed, 01 Feb 2006 15:32:42 +0100, "Paul B. Andersen"
<paul.b.andersen@xxxxxxxxxxxxxxxx> wrote:
Henri Wilson wrote:
If you want to measure the length of a moving object, I suggest you simply take
your tape measure to it and make a reading. You can be quite confident that your tape hasn't changed in any way.
Please explain in detail how to do it.
If I am to measure the length of a _moving_ rod,
I can obviously not run after it with my tape.
Then get in your car and chase it.
When level, check its length with your tape.
Remember to keep one eye on the road though. :)
So how do I use my stationary tape to measure the _moving_ rod?
I see.
You don't know how to do it.
After catching it, you hook one end of your tape onto one end of hte rod then
unwind your tape until part of it reaches the rod's other end and simply read
the scale.
I see.
So you think that a tape stationary to the rod measures
the length of a _moving_ rod?
Of course you don't.
You are evading the question.
You might as well have said:
"Let an observer on the rod measure the length of
the stationary rod, and ask him what the length is."
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
.
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