Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.physics.relativity > #428509

Re: The overpass

Show all headers | View raw

LuigiFortunati wrote:
^^^^^^^^^^^^^^
If “Luigi Fortunati” is your real name, you would be well-advised to insert 
a space. character

> On the overpass C the head A of the train AB encounters the head N of
> the train MN traveling in the opposite direction:
> -------------M------->N------------------------
> ----------------------C---------------------->x
> ----------------------A<-------B---------------
> 
> Since the two trains have the same length and speed, in the land
> reference also the tail B of the train AB encounters the queue M of the
> train MN on the same overpass C:
> ----------------------M------->N---------------
> ----------------------C---------------------->x
> -------------A<-------B------------------------
> 
> At that point, from the tail of both trains a bomb destroys the flyover
> but the trains are now gone and so they are safe.
> 
> Instead, in reference to both trains, the passage of trains on the
> overpass is no longer simultaneous and the train that passes first
> destroys the overpass while the other one has not yet passed.
> 
> So a train perishes.
> 
> In the AB train reference, the MN train is contracted and therefore the
> M tail passes on the overpass (and destroys it) while the tail B of the
> train AB has not yet passed.
> 
> In the AB reference you save the MN train (which passes first) and
> destroy the AB train:
> ----------------------M--->N-------------------
> ----------------------C---------------------->x
> -----------------A<-------B--------------------
> 
> In the MN reference you save the AB train (which passes first) and
> destroy the MN train:
> -----------------M------->N-------------------
> ----------------------C---------------------->x
> -----------------A<---B--------------------
> 
> Which of these scenarios is the right one?

[The proper term is “reference _frame_” or “frame of reference”; and one 
does not say “in reference to”, but “in the (reference) frame of” or “from 
the perspective of” or simply “for”.]

The first scenario is *basically* the right one (but see below), because you 
have not considered length contraction *properly* in the second and third 
scenario.

For AB, MN is shorter *all the way*, so if both trains start with their rear 
ends the same distance away from C (as measured by C), then MN’s front has 
not yet reached C when AB’s front already has.  Thus, AB has enough time to 
pass C:

1.
  -------------M--->N----------------------------
  ----------------------C---------------------->x
  ----------------------A<-------B---------------

2.
  ---------------M--->N--------------------------
  ----------------------C---------------------->x
  --------------------A<-------B-----------------

3.
  -----------------M--->N------------------------
  ----------------------C---------------------->x
  ------------------A<-------B-------------------

4.
  --------------------M--->N---------------------
  ----------------------C---------------------->x
  ---------------A<-------B----------------------

5.
  ----------------------M--->N-------------------
  ----------------------C---------------------->x
  -------------A<-------B------------------------

For MN, AB is shorter *all the way*, so AB’s front has not yet reached C 
when MN’s front has.  Thus, MN has enough time to pass C:

1.
  -------------M------->N------------------------
  ----------------------C---------------------->x
  --------------------------A<---B---------------

2.
  ---------------M------->N----------------------
  ----------------------C---------------------->x
  ------------------------A<---B-----------------

3.
  -----------------M------->N--------------------
  ----------------------C---------------------->x
  ----------------------A<---B-------------------

4.
  -------------------M------->N------------------
  ----------------------C---------------------->x
  --------------------A<---B---------------------

5.
  ----------------------M------->N---------------
  ----------------------C---------------------->x
  -----------------A<---B------------------------

However, you have also neglected length contraction from the perspective of 
an observer in C:

1.
  -------------M----->N--------------------------
  ----------------------C---------------------->x
  ------------------------A<-----B---------------

2.
  ---------------M----->N------------------------
  ----------------------C---------------------->x
  ----------------------A<-----B-----------------

3.
  -----------------M----->N----------------------
  ----------------------C---------------------->x
  --------------------A<-----B-------------------

4.
  -------------------M----->N--------------------
  ----------------------C---------------------->x
  ------------------A<-----B---------------------

5.
  ----------------------M----->N-----------------
  ----------------------C---------------------->x
  ---------------A<-----B------------------------

[You assumed the rest length of a train to be 10 characters, and the moving 
length in the other train’s reference frame to be 6 characters. So the 
moving length in C’s frame should be less then the rest length, but more 
than 6 characters; here, e.g., 8 characters.]

HTH

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

Back to sci.physics.relativity | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

The overpass LuigiFortunati <fortunati.luigi@gmail.com> - 2017-08-13 09:51 +0200
  Re: The overpass Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-13 15:53 +0200
    Re: The overpass Luigi Fortunati <fortunati.luigi@gmail.com> - 2017-08-13 19:13 +0200
      Re: The overpass The Starmaker <starmaker@ix.netcom.com> - 2017-08-13 11:02 -0700
  Re: The overpass Tom Roberts <tjroberts137@sbcglobal.net> - 2017-08-13 09:06 -0500
    Re: The overpass Luigi Fortunati <fortunati.luigi@gmail.com> - 2017-08-13 19:07 +0200
    Re: The overpass Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-13 19:40 +0200
      Re: The overpass Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-13 21:32 +0200
        Re: The overpass Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-13 21:45 +0200
          Re: The overpass Prudence Oppenheimer <phow@innfldo.sp> - 2017-08-13 21:32 +0000
            Re: The overpass Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-14 00:34 +0200
      Re: The overpass Tom Roberts <tjroberts137@sbcglobal.net> - 2017-08-13 23:03 -0500
        Re: The overpass Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-14 15:52 +0200
          Re: The overpass Tom Roberts <tjroberts137@sbcglobal.net> - 2017-08-14 15:21 -0500
            Re: The overpass Tom Roberts <tjroberts137@sbcglobal.net> - 2017-08-14 16:43 -0500
    Re: The overpass "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2017-08-13 17:14 -0700
      Re: The overpass Tom Roberts <tjroberts137@sbcglobal.net> - 2017-08-13 23:04 -0500
        Re: The overpass "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2017-08-14 19:55 -0700

csiph-web