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Nicolaas Vroom

Joined: 30 Apr 2005
Posts: 66

Posted: Thu Jul 20, 2006 4:00 pm    Post subject: Undestanding SR - examination time.

Today you are supposed to do the written examination
in SR physics course 2006.

Consider the thought experiment at
http://users.pandora.be/nicvroom/simultaneity.jpg
with the following modification:
A will be equidistant from the two Firing Devices,
but the distance from the track is zero.
(That means Observer A stands on the track)
You are supposed to do this experiment in real.
The speed of the train is 10 km /hour.
Question: Who will SEE the lights from the two
sources simultaneous ?
1. A
2. B
3. May be A, May be B, or maybe neither A or B,
but never both together.
4. Neither answer 1,2 or 3.

This is the second question.
Exactly the same experiment as above.
The speed is again 10 km/hour.
Assume that A sees the light from the two sources
simultaneous.
You increase the speed of the train.
You do not make any changes to the length of the train.
Question: At different speeds of the train will it be possible
to demonstrate Lorentz (Length) Contraction ?
1. Yes
2. No
3. Neither 1 or 2.

Third question
If Yes do you agree that this implies that the Observer A will
not see the lights simultaneous at different speeds of v ?
(The largest difference if v = c)
1. Yes
2. No
3. Neither 1 or 2.

1. One of the most important aspects of the two questions is that this
experiment is symmetrical. This maybe does not seem obvious at a first
glance. To explain the fact that it is symmetrical you have to compare
the experiment with the "hep" experiment:
http://web.hep.uiuc.edu/home/g-gollin/relativity/p112_relativity_8.html
Replace each antenna with two periscopes.
(One towards the front, one towards the back)
Replace each periscope with one antenna.

When you have made the modifications you can easily see
that the "hep" experiment is symmetrical.
Again you let the two ships approach each other but now you get
two collisions and two flashes (instead of one)
The Nostromo Observer at the centre with his two periscopes
becomes Observer A.
and the Sulaco Observer becomes Observer B

For this modified "hep" experiment you can ask the same questions as above.

2. The second question IMO is the simplest experiment to demonstrate
length contraction (if it is real)
There are no clocks involved.

3. The issue is not if the events ARE simultaneous.

4. Readers have responded that if A sees the events simultaneous
than the events are simultaneous in the reference frame of A.
The same for B.
That is true,
but I do not think that this fact or hypothesis will help you
to define what will be the result of question one and two.

5. In principle no mathematics is involved in this experiment.
Ofcourse you can use mathematics in order to explain the results.

6. Make a drawing.
I do not think that that is the correct way to find the answer.
Ofcourse you can make a drawing to explain that not both
A and B can see the light simultaneous, but again that is not
the complete answer on the question(s).

7. IMO the most common sense answer
for question one is answer 3
(i.e. most probably neither Obsever A nor B will SEE them simultaneous)
and for question two is answer 2 (No)

But this raises new questions.

Nicolaas Vroom
http://users.pandora.be/nicvroom/
dda1
science forum Guru

Joined: 06 Feb 2006
Posts: 762

 Posted: Thu Jul 20, 2006 4:54 pm    Post subject: Nicolaas Vroom - CRETIN. Persistent. Nicolaas Vroom wrote:
Sorcerer1
science forum Guru

Joined: 09 Jun 2006
Posts: 410

Sue...
science forum Guru

Joined: 08 May 2005
Posts: 2684

Posted: Thu Jul 20, 2006 5:59 pm    Post subject: Re: Undestanding SR - examination time.

Nicolaas Vroom wrote:
 Quote: Today you are supposed to do the written examination in SR physics course 2006. This is your first question.

The answer to the first question is:
Trains and lightning don't have any thing to with:
"The Apparent Incompatibility of the Law of Propagation
of Light with the Principle of Relativity"
http://www.bartleby.com/173/7.html

"Retarded potential"
http://farside.ph.utexas.edu/teaching/em/lectures/node50.html

Sue...

wrong question and wrong answer snipped
Nicolaas Vroom

Joined: 30 Apr 2005
Posts: 66

Posted: Thu Jul 20, 2006 6:05 pm    Post subject: Re: Understanding SR

"dda1" <rangeravenger@yahoo.com> schreef in bericht
 Quote: Nicolaas Vroom wrote: snipped due to OP's congenital cretinism

Apperently you know all the answers
but you do not want to share them with us.

Again, Thanks

Nicolaas Vroom
http://usres.pandora.be/nicvroom/
Nicolaas Vroom

Joined: 30 Apr 2005
Posts: 66

Posted: Thu Jul 20, 2006 6:10 pm    Post subject: Re: Undestanding SR - examination time.

"Sue..." <suzysewnshow@yahoo.com.au> schreef in bericht
 Quote: Nicolaas Vroom wrote: Today you are supposed to do the written examination in SR physics course 2006. This is your first question. The answer to the first question is: Trains and lightning don't have any thing to with: "The Apparent Incompatibility of the Law of Propagation of Light with the Principle of Relativity" http://www.bartleby.com/173/7.html "Retarded potential" http://farside.ph.utexas.edu/teaching/em/lectures/node50.html Sue... wrong question and wrong answer snipped

Questions can never be wrong.
Ofcourse not all qustions are clear.
If that is the case you ask for a clarification.

Nicolaas Vroom
http://users.pandora.be/nicvroom/
PD
science forum Guru

Joined: 03 May 2005
Posts: 4363

Posted: Thu Jul 20, 2006 6:17 pm    Post subject: Re: Undestanding SR - examination time.

Nicolaas Vroom wrote:
 Quote: Today you are supposed to do the written examination in SR physics course 2006. This is your first question. Consider the thought experiment at http://users.pandora.be/nicvroom/simultaneity.jpg with the following modification: A will be equidistant from the two Firing Devices, but the distance from the track is zero. (That means Observer A stands on the track) You are supposed to do this experiment in real. The speed of the train is 10 km /hour. Question: Who will SEE the lights from the two sources simultaneous ? 1. A 2. B 3. May be A, May be B, or maybe neither A or B, but never both together. 4. Neither answer 1,2 or 3.

1.

 Quote: This is the second question. Exactly the same experiment as above. The speed is again 10 km/hour. Assume that A sees the light from the two sources simultaneous. You increase the speed of the train. You do not make any changes to the length of the train. Question: At different speeds of the train will it be possible to demonstrate Lorentz (Length) Contraction ? 1. Yes 2. No 3. Neither 1 or 2.

1.

 Quote: Third question If Yes do you agree that this implies that the Observer A will not see the lights simultaneous at different speeds of v ? (The largest difference if v = c) 1. Yes 2. No 3. Neither 1 or 2.

1.

Sorcerer1
science forum Guru

Joined: 09 Jun 2006
Posts: 410

Posted: Thu Jul 20, 2006 7:54 pm    Post subject: Re: Undestanding SR - examination time.

"PD" <TheDraperFamily@gmail.com> wrote in message
|
| Nicolaas Vroom wrote:
| > Today you are supposed to do the written examination
| > in SR physics course 2006.
| >
| > This is your first question.
| > Consider the thought experiment at
| > http://users.pandora.be/nicvroom/simultaneity.jpg
| > with the following modification:
| > A will be equidistant from the two Firing Devices,
| > but the distance from the track is zero.
| > (That means Observer A stands on the track)
| > You are supposed to do this experiment in real.
| > The speed of the train is 10 km /hour.
| > Question: Who will SEE the lights from the two
| > sources simultaneous ?
| > 1. A
| > 2. B
| > 3. May be A, May be B, or maybe neither A or B,
| > but never both together.
| > 4. Neither answer 1,2 or 3.
|
| 1.
|
| >
| > This is the second question.
| > Exactly the same experiment as above.
| > The speed is again 10 km/hour.
| > Assume that A sees the light from the two sources
| > simultaneous.
| > You increase the speed of the train.
| > You do not make any changes to the length of the train.
| > Question: At different speeds of the train will it be possible
| > to demonstrate Lorentz (Length) Contraction ?
| > 1. Yes
| > 2. No
| > 3. Neither 1 or 2.
|
| 1.

ROFLMAO! You can't read, Phuckwit Duck.

"You are supposed to do this experiment in real."
Question: At different speeds of the train will it be possible
to demonstrate Lorentz (Length) Contraction ?

Since you've done it "in real", describe how you demonstrated
cuckoo contraction for a train moving at 10 km/hour. Put the details
in, like location where you performed this experiment, time of day, etc.,
etc.

Androcles.
rotchm@gmail.com
science forum Guru Wannabe

Joined: 14 May 2005
Posts: 111

Posted: Thu Jul 20, 2006 8:14 pm    Post subject: Re: Undestanding SR - examination time.

 Quote: This is your first question. Consider the thought experiment at http://users.pandora.be/nicvroom/simultaneity.jpg

Ambiguity in the question:

"...two electrical devices on the track which are the lenght of the
carriage appart and equidistand from A...."

The carriage is moving...then,

Is it meant that the proper length of the carriage and the proper
length (distance) of the electrical devices are the same? Or does it
mean that the length of the moving carrige (wrt A) is the same length
(distance, wrt A) between the electrical devices?
cirejcon

Joined: 27 May 2005
Posts: 62

Posted: Thu Jul 20, 2006 9:52 pm    Post subject: Re: Undestanding SR - examination time.

Nicolaas Vroom wrote:
 Quote: Today you are supposed to do the written examination in SR physics course 2006. This is your first question. Consider the thought experiment at http://users.pandora.be/nicvroom/simultaneity.jpg

I don't know where this is copied from, but it is
incorrect as written, or at least not well worded.

We are told that the marks on the track are
"a carriage length apart", which I assume
to refer to the carriage length at rest. However,
if that is the case, then Lorentz contraction
will cause the train to shorten and trigger 1
will fire before trigger 2. That's in the
frame of A. In the frame of B, the track
is shortened and trigger 2 fires before 1.

The paragraph can only be correct
if the spacing of the triggers already includes
the effect of the Lorentz contraction,
which is mathematically possible, but
a strange way to set up the problem.
Nevertheless, if that's what was meant,
then A would indeed see the lights
fire simultaneously, but B would still
claim the track had shortened (even more)
and claim 2 fired before 1.

 Quote: with the following modification: A will be equidistant from the two Firing Devices, but the distance from the track is zero. (That means Observer A stands on the track) You are supposed to do this experiment in real. The speed of the train is 10 km /hour. Question: Who will SEE the lights from the two sources simultaneous ? 1. A 2. B 3. May be A, May be B, or maybe neither A or B, but never both together. 4. Neither answer 1,2 or 3.

As I said, depending on how the wording is interpreted,
it could be 1 (ie, the wording is incorrect), or 4
(the wording is correct but misleading).

 Quote: This is the second question. Exactly the same experiment as above. The speed is again 10 km/hour. Assume that A sees the light from the two sources simultaneous. You increase the speed of the train. You do not make any changes to the length of the train. Question: At different speeds of the train will it be possible to demonstrate Lorentz (Length) Contraction ? 1. Yes 2. No 3. Neither 1 or 2.

In order for one to assume the lights are simultaneous
when the train is moving 10 km/hr, then, as I said before,
the marks on the track would have to be corrected
for the Lorentz contraction at *exactly that speed*,
and they would not be simultaneous for any other
speed, so the answer is 1.

 Quote: Third question If Yes do you agree that this implies that the Observer A will not see the lights simultaneous at different speeds of v ? (The largest difference if v = c) 1. Yes 2. No 3. Neither 1 or 2.

1, in any case.

 Quote: Comments. 1. One of the most important aspects of the two questions is that this experiment is symmetrical.

It is not symmetrical.

What you are trying to do is set up a case where observers
A and B are in the same place when the lights fire, but that's not the
end
of the story. Remember, they are still moving, so regardless of
where they are when the lights trigger, *they will be in different
places when the light reaches them*. You have to take
that into account when working out when each of them will
"see" the lights fire.

-jc
PD
science forum Guru

Joined: 03 May 2005
Posts: 4363

Posted: Thu Jul 20, 2006 10:12 pm    Post subject: Re: Undestanding SR - examination time.

Sorcerer wrote:
 Quote: "PD" wrote in message news:1153419427.249519.254840@b28g2000cwb.googlegroups.com... | | Nicolaas Vroom wrote: | > Today you are supposed to do the written examination | > in SR physics course 2006. | | > This is your first question. | > Consider the thought experiment at | > http://users.pandora.be/nicvroom/simultaneity.jpg | > with the following modification: | > A will be equidistant from the two Firing Devices, | > but the distance from the track is zero. | > (That means Observer A stands on the track) | > You are supposed to do this experiment in real. | > The speed of the train is 10 km /hour. | > Question: Who will SEE the lights from the two | > sources simultaneous ? | > 1. A | > 2. B | > 3. May be A, May be B, or maybe neither A or B, | > but never both together. | > 4. Neither answer 1,2 or 3. | | 1. | | | > This is the second question. | > Exactly the same experiment as above. | > The speed is again 10 km/hour. | > Assume that A sees the light from the two sources | > simultaneous. | > You increase the speed of the train. | > You do not make any changes to the length of the train. | > Question: At different speeds of the train will it be possible | > to demonstrate Lorentz (Length) Contraction ? | > 1. Yes | > 2. No | > 3. Neither 1 or 2. | | 1. ROFLMAO! You can't read, Phuckwit Duck. "You are supposed to do this experiment in real." Question: At different speeds of the train will it be possible to demonstrate Lorentz (Length) Contraction ?

I answered the question "will it be possible?". I did not say that it
had been done and therefore was shown to be possible, nor that I did it
myself with trains. You apparently can't read, Androcles.

 Quote: Since you've done it "in real", describe how you demonstrated cuckoo contraction for a train moving at 10 km/hour. Put the details in, like location where you performed this experiment, time of day, etc., etc. Androcles.
Martin Hogbin
science forum Guru

Joined: 30 Apr 2005
Posts: 366

Posted: Thu Jul 20, 2006 10:25 pm    Post subject: Re: Undestanding SR - examination time.

"Sorcerer" <Headmaster@hogwarts.physics_a> wrote in message news:bGOvg.413\$I9.65@fe2.news.blueyonder.co.uk...
 Quote: "Nicolaas Vroom" wrote in message news:zMNvg.547489\$ww7.12757024@phobos.telenet-ops.be... | Today you are supposed to do the written examination | in SR physics course 2006. | | This is your first question. | Consider the thought experiment at | http://users.pandora.be/nicvroom/simultaneity.jpg Solved at: http://www.androcles01.pwp.blueyonder.co.uk/Rocket/Rocket.htm Animations are better than still pictures, there is less to imagine.

Go gettim Androcles.

Martin Hogbin
Sorcerer1
science forum Guru

Joined: 09 Jun 2006
Posts: 410

Sorcerer1
science forum Guru

Joined: 09 Jun 2006
Posts: 410

 Posted: Thu Jul 20, 2006 10:54 pm    Post subject: Re: Undestanding SR - examination time. "Martin Hogbin" wrote in message news:IuKdnYrxOaMfn13ZnZ2dnUVZ8smdnZ2d@bt.com... | | "Sorcerer" wrote in message news:bGOvg.413\$I9.65@fe2.news.blueyonder.co.uk... | > | > "Nicolaas Vroom" wrote in message | > news:zMNvg.547489\$ww7.12757024@phobos.telenet-ops.be... | > | Today you are supposed to do the written examination | > | in SR physics course 2006. | > | | > | This is your first question. | > | Consider the thought experiment at | > | http://users.pandora.be/nicvroom/simultaneity.jpg | > | > Solved at: | > http://www.androcles01.pwp.blueyonder.co.uk/Rocket/Rocket.htm | > | > Animations are better than still pictures, there is less to imagine. | | Go gettim Androcles. | | Martin Hogbin You can't fault the derivation of the cuckoo transformations, Pigbin, they are Einstein's. All I did was make a picture of it to explain how the trick is done. Androcles.
Sue...
science forum Guru

Joined: 08 May 2005
Posts: 2684

Posted: Fri Jul 21, 2006 9:10 am    Post subject: Re: Undestanding SR - examination time.

Nicolaas Vroom wrote:
 Quote: "Sue..." schreef in bericht news:1153418349.067109.326330@i3g2000cwc.googlegroups.com... Nicolaas Vroom wrote: Today you are supposed to do the written examination in SR physics course 2006. This is your first question. The answer to the first question is: Trains and lightning don't have any thing to with: "The Apparent Incompatibility of the Law of Propagation of Light with the Principle of Relativity" http://www.bartleby.com/173/7.html "Retarded potential" http://farside.ph.utexas.edu/teaching/em/lectures/node50.html Sue... wrong question and wrong answer snipped Questions can never be wrong. Ofcourse not all qustions are clear. If that is the case you ask for a clarification. Only Answers can be wrong.

If a physics teacher said in a lecture "suppose
DHHell Courier uses near luminal aircraft..."

....Then proceeds scribbling time and distance
calulations on the chalk board. Sure, there is nothing
wrong with that.

But if you, as a student in the class, were then
tested on the technical details of the craft, fuel
skin temperature, landing gear etc, you would
scream bloody murder that the test is outside
the scope of the course material.

You are doing no less ill, focusing on the details of an
imginary train when the subject material is

---the isotropy of light propagation---

You are abusing the theorist's attempt to explain
something very complex, in lay terms and that is 'wrong'.
..
If you don't want to learn electromagnetism so you
can discuss the subject intellegently and you
just want to weseal-word and play semantics,
then you'll find nicer company in a group than
doesn't have 'sci' for the first three letters.

Sue...

http://www.bartleby.com/173/
http://farside.ph.utexas.edu/teaching.html
http://web.mit.edu/8.02t/www/802TEAL3D/teal_tour.htm

 Quote: Nicolaas Vroom http://users.pandora.be/nicvroom/

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