# Basic Special Relativity Question

Discussion in 'Physics & Math' started by Fednis48, Apr 22, 2013.

1. ### PeteIt's not rocket surgeryRegistered Senior Member

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Frustration is reaching a peak. Time to call a moderator. I'll message James and AN.

3. ### TachBannedBanned

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$y_B''(t'')-y_A''(t'')=-u\gamma'(t'' + \frac{Vx_B''}{c^2})+u\gamma'(t'' + \frac{Vx_A''}{c^2})$

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7. ### TachBannedBanned

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Reduce the like terms. Do you think you can do that all by yourself, without calling the mods? Looks like you already called them.

8. ### PeteIt's not rocket surgeryRegistered Senior Member

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I've done that, Tach. You can see my result in the opening post. I've checked it, and can see no mistake.

9. ### Fednis48Registered Senior Member

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Thank you for this. In my most recent post, I thought about writing that my primary goal had shifted from resolving this debate to getting Tach formally punished for trolling, but I thought that might be overstepping my bounds as a newcomer.

10. ### PeteIt's not rocket surgeryRegistered Senior Member

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Hi Russ, I don't know if you'll see this response with all the noise in between.

This is interesting because the rod is measured to be temporarily bent at times in the platform frame, after accounting for signal delays.

In the train frame, the rod falls level, like this:

In the platform frame, the rod falls at an angle, like this:

(The diagrams were constructed using Python. The distance and time scales are accurate.)

brucep,
No, this doesn't mean there is a paradox.
If you attach a bunch of strain gauges or other force-detectors to the rod, they'd show the same result in both reference frames.

Last edited: Apr 23, 2013
11. ### Fednis48Registered Senior Member

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Cool pics! Did you do that in MATLAB or something?

12. ### brucepValued Senior Member

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The results do agree in both reference frames after the appropriate transformations are completed. The remote coordinate frame measurements when transformed to the local proper frame agree. That's the basic concept of relativity theory. That includes when the bar was released completely in the invariant local proper frame.

13. ### TachBannedBanned

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$y_B''(t'')-y_A''(t'')=-u\gamma'(t'' + \frac{Vx_B''}{c^2})+u\gamma'(t'' + \frac{Vx_A''}{c^2})=\frac{Vu\gamma'}{c^2}(x_A''-x_B'')$

This is getting ridiculous, only because you are clearly unwilling to admit to error.

14. ### PeteIt's not rocket surgeryRegistered Senior Member

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I've learned some basic Python with Matplotib over the last week or two. Was kind of a steep learning curve, but I should be able to make animations much faster now.
I wrote some Python code to spit out a bunch of .png images, then used ImageMagick Convert to compile them into animated gifs.

15. ### Fednis48Registered Senior Member

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That is exactly what I have in post 44. I agree with it, assuming you do.

16. ### TachBannedBanned

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But Pete STILL doesn't see it. And you took forever to see it, once you figured out your basic errors, you became abusive. You should be upset with yourself, not take it on me.

17. ### PeteIt's not rocket surgeryRegistered Senior Member

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Thanks Tach, you're taking a different line of algebra than I did. I'll check it out.

18. ### TachBannedBanned

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Maybe you should call off the mods, eh?

19. ### RJBeeryNatural PhilosopherValued Senior Member

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Ahh! See, that's how Tach thinks he "wins". He's not an elitist; he's a sad little man. It's possible that a mistake exists, but it's also possible that Tach used a symbolic computation system to derive the WRONG answer and therefore cannot tell you where you went wrong. He did that very thing here and the proceeded to tout his wrong answer for an entire week, "challenging" others to duplicate it! Complete fraud. Anyway, don't base your progress whatsoever on Tach's responses (or lack of them...which will occur as soon as he has nowhere else to run).

20. ### Fednis48Registered Senior Member

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Ah, I see it now. Pete: the problem is that, in your original post, you incorrectly plug in the values of $x''$ and forget to distribute a minus sign. If you look at post 27, where I break things down into steps, it's going from $3\rightarrow 4$ (specifically, the second term in 4) that is wrong. When done right, we do indeed get $-\frac{Vu\gamma'}{c^2}$, like Tach said.

Tach: I didn't get abusive after I found my error. I just now found my error. I got abusive because it's taken four pages to find an error that should have been found in 10 posts or less. In over a dozen posts, you've never actually pointed to the specific line in Pete's calculation that was wrong. Instead you've asked us over and over to calculate $\frac{y''_B-y''_A}{x''_B-x''_A}$ according to our own expressions, when the error was actually in calculating $y''_B$ itself.

21. ### TachBannedBanned

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Fail. Again. Troll.

22. ### Fednis48Registered Senior Member

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I know, I know

. In this case, it looks like there was a mistake, and I'm glad Tach "helped" me find it. But you're quite right - he seems to enjoy watching others struggle to reproduce his conclusions more than he enjoys helping them do so. That's why I say he's elitist. (And for what it's worth, that's not mutually exclusive with being a sad little man.)

23. ### TachBannedBanned

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There is no excuse for you to become abusive, especially since you were wrong all along.

There is value in learning how to find your own errors. It is not my fault that you two are so blind to your faults. Maybe next time around you will learn how to follow the hints, they were pretty basic.

I narrowed down the calculations for the you two by eliminating the line in error. Still took 9 hours to even accept that your result is wrong. Pete hasn't even acknowledged yet.