Physics Emergency: Two Trains Moving Away at 51% Light Speed

  • Context: Graduate 
  • Thread starter Thread starter Rico Bamchug
  • Start date Start date
  • Tags Tags
    Physics
Click For Summary

Discussion Overview

The discussion revolves around the relativistic effects of two trains moving away from each other at 51% the speed of light, specifically addressing how their relative speeds are perceived from each train's frame of reference. The scope includes theoretical considerations of special relativity and the application of the relativistic velocity addition formula.

Discussion Character

  • Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions whether, from one train's perspective, the other train would appear to be traveling at 102% the speed of light.
  • Another participant responds by stating that the relativistic velocity addition formula must be used, calculating that the other train would actually be moving at approximately 80.946% the speed of light.
  • A further contribution emphasizes the importance of specifying the frame of reference when discussing speeds, suggesting that clarity is achieved by stating "as measured..." to indicate relative motion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial question posed, but there is agreement on the necessity of using the relativistic velocity addition formula and the importance of specifying reference frames.

Contextual Notes

The discussion does not resolve the implications of the relativistic effects in practical scenarios, nor does it address potential misunderstandings about the nature of speed in relativity.

Rico Bamchug
Messages
2
Reaction score
0
Okay, I made a statement in another forum completely unrelated to physics and I believe it to be wrong even though I made the statement in good faith. (Which is to say, I THOUGHT I knew what I was talking about.)

So please, if you can, bail me out.

Two trains are moving away from each other, both traveling at 51% the speed of light. In one train, viewing the other, would it appear to be traveling at 102% the speed of light?

Okay, that's it! Any help will be greatly appreciated!
 
Physics news on Phys.org
Rico Bamchug said:
Okay, I made a statement in another forum completely unrelated to physics and I believe it to be wrong even though I made the statement in good faith. (Which is to say, I THOUGHT I knew what I was talking about.)

So please, if you can, bail me out.

Two trains are moving away from each other, both traveling at 51% the speed of light. In one train, viewing the other, would it appear to be traveling at 102% the speed of light?
Nope, you have to use the relativistic velocity addition formula here--in one train's frame, the other train will be moving at (0.51c + 0.51c)/(1 + 0.51^2) = 0.80946c, i.e. 80.946% the speed of light.
 
Awesome! And thank you Jesse!
 
Whenever you talk about this kind of problem, it helps to always add "as measured ..." When you say a train is moving at 0.51c, state relative to what or measured relative to what. That helps keep things straight.
 

Similar threads

Undergrad Variation of the lightning train thought experiment
  • · Replies 26 ·
Replies
26
Views
5K
High School Thought Experiment: Behavior of shadow of object moving at speed c
  • · Replies 14 ·
Replies
14
Views
2K
Undergrad A problem with how the speed of light connects to special relativity
  • · Replies 12 ·
Replies
12
Views
2K
High School What Would Light Look Like If Train Moved at > Speed of Light?
  • · Replies 12 ·
Replies
12
Views
3K
Undergrad Can the intersection point of two light beams exceed the speed of light?
  • · Replies 9 ·
Replies
9
Views
1K
High School Train traveling near light speed
  • · Replies 18 ·
Replies
18
Views
3K
High School Train platform -- light speed and time quandry
  • · Replies 14 ·
Replies
14
Views
3K
High School Prove the velocity of a moving object is absolute in one IRF?
  • · Replies 22 ·
Replies
22
Views
2K
High School Constancy of the speed of light
  • · Replies 83 ·
3
Replies
83
Views
9K
Undergrad A question about the speed of light and electromagnetism
  • · Replies 51 ·
2
Replies
51
Views
5K