Einstein's Electrodynamics of moving Bodies

AI Thread Summary
The discussion revolves around understanding Einstein's theory of special relativity, specifically the concept of length contraction. The user expresses confusion about applying the equation L = L0√(1 - v²/c²) and identifying L0, which represents the length in the rest frame. Suggestions are made to consult additional resources, such as textbooks and lecture notes, to gain a clearer understanding of the topic. A recommendation is provided for a free book on special relativity that could help clarify these concepts. Overall, the user seeks guidance on how to approach problems related to moving bodies and their electrodynamics.
jselms99
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Homework Statement
Okay guys I’m lost:

I have a train measured as being 100 meters in length standing in the station. Once its pulled out and it reaches a constant speed, the length measured by observers who are alongside the tracks is 50 meters. How fast is it traveling?

I have to calculate this for different distances; for example, 10 meters, 50 meters, 100 meters and represent the answer as a fraction of c.
Relevant Equations
The problem is, I don’t know what equation I should be using!
Okay I’m assuming I have to use √1- v^2/c^2 multiplied by some coefficient of length but I don’t understand any of this and could really use help understanding the process and/or reference material that might point me in the right direction
 
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Hello @jselms99 ,
:welcome: ##\qquad## !​

Here at PF we have some rules and guidelines, which please read. In particular: we need some attempt from you before we can help.

jselms99 said:
The problem is, I don’t know what equation I should be using!

Okay I’m assuming I have to use √1- v^2/c^2 multiplied by some coefficient of length but I don’t understand any of this and could really use help understanding the process and/or reference material that might point me in the right direction
Do you have a textbook, lecture notes, anything relevant for this exercise ?
If not, why are you doing this ?

Perhaps you can read up on 'length contraction' ?

##\ ##
 
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BvU said:
Hello @jselms99 ,
:welcome: ##\qquad## !​

Here at PF we have some rules and guidelines, which please read. In particular: we need some attempt from you before we can help.Do you have a textbook, lecture notes, anything relevant for this exercise ?
If not, why are you doing this ?

Perhaps you can read up on 'length contraction' ?

##\ ##
I don’t have notes or anything except Einstein’s 1905 paper “On the Electrodynamics of Moving Bodies” which is currently breaking my brain…. From what I’ve read about length contraction, the equation L = Lo √1- v^2/c^2 may apply but I’m having difficulty identifying Lo
 
##L_0## is length in rest frame (i.e. when measured in frame where train stands still, for example standing at the station).
 
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BvU said:
##L_0## is length in rest frame (i.e. when measured in frame where train stands still, for example standing at the station).
How would I account for varying distances traveled though? I was thinking of using the equation x=vt and t=x’/(c-v) but I don’t know if that’s helpful
 
Could you transcribe the entire problem : as is, the "different distances... for instance...." makes no sense to me without quite a bit of context.
 
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jselms99 said:
I don’t have notes or anything except Einstein’s 1905 paper “On the Electrodynamics of Moving Bodies” which is currently breaking my brain…. From what I’ve read about length contraction, the equation L = Lo √1- v^2/c^2 may apply but I’m having difficulty identifying Lo
That's a great paper, but it's not a good source for you to learn SR from. As is evidenced by your helplessness in the face of a length contraction problem.

Try this. The first chapter is free.

https://scholar.harvard.edu/david-morin/special-relativity
 
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