Discussion in 'Physics & Math' started by renislaj, Apr 18, 2013.

1. ### TachBannedBanned

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You are repeating the same error posted by Undefined

You are under a very severe delusion that your post 151 proves anything.

3. ### Fednis48Registered Senior Member

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By insinuating that GR and SR are not equivalent in the appropriate limit, you're doing a serious disservice to any non-experts reading this thread.

And after half a dozen posts begging you to point out any error in post 151, your response is that I'm "delusional". It's been a while since I debated trolls on a forum, so thanks for reminding me why I don't do that, I guess.

5. ### TachBannedBanned

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Nah, I was just pointing out that you don't know what the weak limit means, that's all.

7. ### Fednis48Registered Senior Member

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Oh, ok. What does it mean?

8. ### TachBannedBanned

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Something totally different from what you think.

9. ### Fednis48Registered Senior Member

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Fair enough. I don't really know squat about metrics, so someone with more of a background in relativity would have to tell me whether a rod falling a few meters under Earth's gravity satisfies the low-field limit. Meanwhile, answer post 151. Your refusal to do so with anything other that condescending dismissals has gone from understandable, to frustrating, to simply childish.

10. ### TachBannedBanned

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You should learn. But first, some basic algebra.

11. ### Fednis48Registered Senior Member

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Cute. If you have a problem with something I wrote in the other thread, answer it in the other thread. Respond to post 151.

12. ### UndefinedBannedBanned

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I don't understand what you are saying. You confuse me because you say the rod frame is inertial? But if you said before that GR is involved, how can the rod frame be inertial? The only way the rod frame can be treated as inertial is if we do as I naively understood to be what physicists do when removing GR from consideration, by making it an insignificant GR field and go from there as SR and inertial rod frame is consistent with that. But you keep saying both train and platform frames are accelerated frames, even though rod frame is inertial. I am lost as to what you are saying should or should not be the "formalism", but you keep confusing me with all your mixing up of frames and formalisms like in the above quote about rod frame being inertial frames while train and platform being accelerated frames. I don't get what you mean yet. Confused more and more by that sort of explanation. Can anybody clear that up for me simply one way or the other formalism and frameworks involved?

13. ### TachBannedBanned

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Nope, the rod is free-falling. Free falling frames are inertial.
On the other hand, both the platform and the train are non-inertial frames (by virtue of being accelerated upwards).

You will need to learn that GR treats frames differently than Newtonian mechanics. You are using your Newtonian intuition in GR, it doesn't work this way.

14. ### UndefinedBannedBanned

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How are train and platform being "accelerated upwards"?

15. ### TachBannedBanned

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No more free lessons for you, find a class that you can take somewhere.

16. ### UndefinedBannedBanned

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Is it your secret? Why stop now? You say they are both accelerated upwards, the least you can do is support that before you sneak away with some excuse or other for not answering a question about why you think "train and platform are both accelerated upwards". Then I can answer agree or disagree and explain my reasons why. Just like real science debaters should do?

17. ### TachBannedBanned

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No, it's not a secret, anyone who studied GR learned about it. You should try it , too.

18. ### eramSciengineerValued Senior Member

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I think what he meant was, he wanted you to elaborate.

19. ### Fednis48Registered Senior Member

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In GR, an inertial frame is one that is freefalling under gravity. The rod is freefalling, so its frame is an inertial frame. On the other hand, the train and platform are not freefalling; they are staying at constant height. Classically, we would say their acceleration is zero. But in GR, the inertial frame is one that's accelerating down at a rate g, so a constant-height frame is accelerating up at a rate g by comparison.

A good way to think of it is to imagine yourself in the inertial frame. If you were freefalling, it would look like the ground was rushing up to meet you!

Last edited: Apr 23, 2013
20. ### TachBannedBanned

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"At rest with respect to gravity"? Did you read this somewhere or did you make it up all by yourself?

"A rest frame" for what? Your butchering of GR concepts is hilarious.

"rest frame", again?

You would benefit from taking a class before you start pretending to teach others.

21. ### Fednis48Registered Senior Member

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Whoops - egg on my face! In all instances where I said "rest frame", I should have said "inertial frame". My specialty is quantum mechanics, so I'm not very used to relativistic terminology.

I've edited the original post to make it right.

22. ### UndefinedBannedBanned

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You take time and trouble to make remarks to Fednis48, but you can't take one moment to support with explanation what you mean when you say "both train and platform frames are accelerated frames". If you don't support your argument then I cannot believe you know what you are saying. Please do me the special personal favor and kindly just explain that bit more so I can better understand the discussion from now on. Please please please?

23. ### UndefinedBannedBanned

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I naively understood that the situation is that both train and rod are inertial once motion of rod is established as a constant closing speed with the train floor (or relatively vice versa, but still inertial after whatever "starting impulse" created the relative motion of the rod towards the floor). No acceleration during the closing as far as I naively understand the exercise without GR or further input to rod or train, as the movements in transit are all relative not accelerated absolutes between rod and train roof/floor in both train and rod frames when gravity is effectively ignored in the very weak field case?

Last edited: Apr 24, 2013