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Re: Relative motion again

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On 6/11/2018 1:45 pm, benj wrote:
> On 11/5/2018 9:16 PM, Sylvia Else wrote:
>> On 6/11/2018 5:49 am, xip1415926@gmail.com wrote:
>>> Some guy walks out of a bar…
>>>
>>> Well, almost.
>>>
>>> Actually, two guys walk out of two bars, these guys being of about 
>>> equal weight, mass = 150 lbs, and equal walking speed, 2 mph. They 
>>> turn right and left on leaving doorways, thereby approaching each 
>>> other on the sidewalk.
>>>
>>> Walker-A has speed a = 2 and walker-B has speed b = 2, speeds 
>>> conveniently positive though of opposite directions.
>>>
>>> Relative motion of the walkers is convergence.  Walkers A and B 
>>> approach one another with speed v = a + b = 2 + 2 = 4.
>>>
>>
>> This is wrong. You are making the unfounded assumption that velocities 
>> combine by addition, when they do not. The difference is negligible 
>> for small velocities, but large when the magnitudes of the velocities 
>> approach the speed of light.
>>
>> Sylvia.
> 
> You are simply wrong Sylvia. By the principle of Galilean relativity, if 
> the two guys walk out of the bar and approach each other it would not 
> matter if both of them were traveling near the speed of light. To each 
> other they would be traveling slow. But to an observer across the street 
> things would appear quite different. And the reason would be retardation 
> not relativity. Or do you believe as they approach the speed of light 
> the sidewalk shortens?

If they're both travelling near the speed of light relative to the 
street in the same direction, but one is travelling slightly faster than 
the other relative to the street, then that would be true.

The OP's scenario relates to two people travelling in opposite 
directions relative to the street, and the OP then seeks to deduce the 
speed of one person relative to the other, and does so incorrectly based 
on the assumption that velocities combine by addition.

Sylvia

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Relative motion again xip1415926@gmail.com - 2018-11-05 10:49 -0800
  Re:Relative motion again Libor Striz <poutnik4REMOVEnntp@CAPITALSgmail.com> - 2018-11-05 20:16 +0100
    Re:Relative motion again Buck Dehner <uktea@yswdoiz.cp> - 2018-11-05 21:07 +0000
      Re:Relative motion again Libor Striz <poutnik4REMOVEnntp@CAPITALSgmail.com> - 2018-11-05 22:55 +0100
        Re:Relative motion again Buck Dehner <uktea@yswdoiz.cp> - 2018-11-05 22:46 +0000
          Re:Relative motion again Libor Striz <poutnik4REMOVEnntp@CAPITALSgmail.com> - 2018-11-06 01:22 +0100
            Re:Relative motion again Ntowicz Usarczyk <iswso@wioioksi.io> - 2018-11-06 20:27 +0000
  Re: Relative motion again Sylvia Else <sylvia@email.invalid> - 2018-11-06 13:16 +1100
    Re: Relative motion again benj <benj.fake@gmail.com> - 2018-11-05 21:45 -0500
      Re: Relative motion again Sylvia Else <sylvia@email.invalid> - 2018-11-06 14:57 +1100
    Re: Relative motion again xip1415926@gmail.com - 2018-11-05 19:58 -0800
      Re: Relative motion again xip1415926@gmail.com - 2018-11-05 21:24 -0800
      Re: Relative motion again Sylvia Else <sylvia@email.invalid> - 2018-11-06 18:10 +1100
      Re: Relative motion again Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-11-06 09:21 +0100
        Re: Relative motion again xip1415926@gmail.com - 2018-11-06 06:03 -0800
          Re: Relative motion again Tom Roberts <tjroberts137@sbcglobal.net> - 2018-11-06 08:41 -0600
            Re: Relative motion again Ntowicz Usarczyk <iswso@wioioksi.io> - 2018-11-06 20:32 +0000
              Re: Relative motion again Tom Roberts <tjroberts137@sbcglobal.net> - 2018-11-06 20:39 -0600
                Re: Relative motion again Ntowicz Usarczyk <iswso@wioioksi.io> - 2018-11-07 19:44 +0000
          Re: Relative motion again Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-11-06 22:32 +0100

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