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Old 21st July 2018, 01:57 AM   #1
SDG
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Pendular Motion (And Relativity)

Mod InfoThis thread is split from The Theory of Relativity thread.
Posted By:Loss Leader




There is a thread on thenakedscientists forum about pendulum and conservation of energy.
The issue is rotational kinetic energy that 'apparently breaks' relativity.

There are many smart people on that forum but nobody is defending relativity.
What's going on? How to debunk the claim?
Some healthy skepticism is needed.

Last edited by Loss Leader; 22nd July 2018 at 05:01 PM.
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Old 21st July 2018, 02:49 AM   #2
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Originally Posted by SDG View Post
There is a thread on thenakedscientists forum about pendulum and conservation of energy.
The issue is rotational kinetic energy that 'apparently breaks' relativity.

There are many smart people on that forum but nobody is defending relativity.
What's going on? How to debunk the claim?
Some healthy skepticism is needed.
Interresting
Do you have a link
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Old 21st July 2018, 03:55 AM   #3
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No, I am a newbie, I cannot post links.
Just check the forum.
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Old 21st July 2018, 03:56 AM   #4
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Originally Posted by SDG View Post
No, I am a newbie, I cannot post links.
Just check the forum.
The rule is to prevent spam bots flooding the forum. If you post the link with full stops replaced by spaces, say, someone will convert it into a clickable link for you.
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Old 21st July 2018, 04:08 AM   #5
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thenakedscientists
com/forum/index
php?topic=73606

New lines are dots
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Old 21st July 2018, 04:11 AM   #6
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Originally Posted by SDG View Post
thenakedscientists
com/forum/index
php?topic=73606

New lines are dots
https://www.thenakedscientists.com/f...hp?topic=73606

Welcome to the forum.
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Old 21st July 2018, 04:13 AM   #7
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Originally Posted by Pixel42 View Post
Welcome to the forum.
Thank you!
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Old 22nd July 2018, 04:10 AM   #8
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Originally Posted by SDG View Post
There is a thread on thenakedscientists forum about pendulum and conservation of energy.
The issue is rotational kinetic energy that 'apparently breaks' relativity.

There are many smart people on that forum but nobody is defending relativity.
What's going on? How to debunk the claim?
Some healthy skepticism is needed.
I have not read all details, but it seems that the person asking is unable to cope with approximation. I can't see what it has to do with relativity.

As somebody remarks in that forum, either you use a model with a lot of approximations (like leaving out various negligible factors), or you use a model with a lot of complex math.

Hans
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Old 22nd July 2018, 08:51 AM   #9
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Originally Posted by MRC_Hans View Post
I have not read all details, but it seems that the person asking is unable to cope with approximation. I can't see what it has to do with relativity.

As somebody remarks in that forum, either you use a model with a lot of approximations (like leaving out various negligible factors), or you use a model with a lot of complex math.

Hans
Well, the only aspect of relativity I saw, MRC_Hans, on my quick perusal. Was a claim that due to the approximation and its limitations one could devise an experiment to detect constant linear motion without external references. However, as noted the approximation is just that, approximate, and used in reference to simplifying a rotating reference frame. So beside being just approximate it just wouldn't be applicable to simple linear motion. Again that's just my take from a quick scan of the link.
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Old 22nd July 2018, 12:47 PM   #10
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Originally Posted by MRC_Hans View Post
I have not read all details, but it seems that the person asking is unable to cope with approximation. I can't see what it has to do with relativity.
Have you checked the post #8 in that thred?
Is this what you are talking about?
Quote:

As somebody remarks in that forum, either you use a model with a lot of approximations (like leaving out various negligible factors), or you use a model with a lot of complex math.

Hans
Can we go slowly?
Is there any issue with the post #1 in the thread?
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Old 22nd July 2018, 12:53 PM   #11
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Originally Posted by The Man View Post
Well, the only aspect of relativity I saw, MRC_Hans, on my quick perusal. Was a claim that due to the approximation and its limitations one could devise an experiment to detect constant linear motion without external references. However, as noted the approximation is just that, approximate, and used in reference to simplifying a rotating reference frame. So beside being just approximate it just wouldn't be applicable to simple linear motion. Again that's just my take from a quick scan of the link.
I am not sure you understand the issue here.
There is no talk about the rotating reference frame.
It appears you need to put more effort to understand what is at stake here.
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Old 22nd July 2018, 01:30 PM   #12
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Originally Posted by SDG View Post
I am not sure you understand the issue here.
There is no talk about the rotating reference frame.
It appears you need to put more effort to understand what is at stake here.
Well, why don't you explain it?

Hans
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Old 22nd July 2018, 01:38 PM   #13
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Originally Posted by SDG View Post
I am not sure you understand the issue here.
There is no talk about the rotating reference frame.
It appears you need to put more effort to understand what is at stake here.

Nope, I put in all the effort it was worth. As I recall the pendulum is freely rotating so in a reference frame rotating with the pudendum it would just be swinging back and forth like a non-rotating pendulum. Someone even makes, as I recall, the comparison to a train wheel where in one frame the wheel just rotates while in another a point on the wheel would have a sinusoidal motion. I see nothing "at stake here".

ETA:
Heck, it was the freely rotating and train wheel parts that brought this type of pendulum to mind...

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as the situation being discussed.
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Old 23rd July 2018, 01:16 AM   #14
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Originally Posted by MRC_Hans View Post
Well, why don't you explain it?



Hans


It appears there are two reference frames: ground and moving train, in the post #8.
The rotating wheel does circular motion in the train frame and it does cycloidal motion in the ground frame.

Where is the rotating reference frame?


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Old 23rd July 2018, 01:26 AM   #15
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Originally Posted by The Man View Post
Nope, I put in all the effort it was worth. As I recall the pendulum is freely rotating so in a reference frame rotating with the pudendum it would just be swinging back and forth like a non-rotating pendulum. Someone even makes, as I recall, the comparison to a train wheel where in one frame the wheel just rotates while in another a point on the wheel would have a sinusoidal motion. I see nothing "at stake here".

ETA:
Heck, it was the freely rotating and train wheel parts that brought this type of pendulum to mind...

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE


as the situation being discussed.


You lost me.
Quote:
As I recall the pendulum is freely rotating so in a reference frame rotating with the pudendum it would just be swinging back and forth like a non-rotating pendulum.
I have no idea what you are saying here.


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Old 23rd July 2018, 05:26 AM   #16
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Originally Posted by SDG View Post
It appears there are two reference frames: ground and moving train, in the post #8.
The rotating wheel does circular motion in the train frame and it does cycloidal motion in the ground frame.

Where is the rotating reference frame?


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Let me recap ...

You, SDG, wrote: "I am not sure you understand the issue here.
There is no talk about the rotating reference frame.
It appears you need to put more effort to understand what is at stake here.
"

To which MRC_Hans said "Well, why don't you explain it?"

I too am puzzled; when you wrote "what is at stake here", what did you mean? Likewise, "understand the issue here"

What, specifically, is "at stake"? What is "the issue here"?
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Old 23rd July 2018, 08:37 AM   #17
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Originally Posted by JeanTate View Post
Let me recap ...

You, SDG, wrote: "I am not sure you understand the issue here.
There is no talk about the rotating reference frame.
It appears you need to put more effort to understand what is at stake here.
"

To which MRC_Hans said "Well, why don't you explain it?"

I too am puzzled; when you wrote "what is at stake here", what did you mean? Likewise, "understand the issue here"

What, specifically, is "at stake"? What is "the issue here"?
There is no analysis from within the accelerated rotating reference frame.
The rotating reference frame has nothing to do with the analysis of the ground and moving frame. This is a demonstration that the poster does not understand post #8 from the other forum.

What is at stake? The poster claims the experiment in the post #8 can detect linear straight motion without any signal from the outside. The relativity says this is not possible! If that experiment turns out to be true then the relativity as we know it is dead. This is what is at stake here.

As I said in the OP, there are many smart people on that forum and nobody jumps into the defense of the relativity. How come? What is going on?

So can we come up with something? Healthy skepticism? Where is the mistake in the proposed analysis?
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Old 23rd July 2018, 08:41 AM   #18
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Originally Posted by SDG View Post
It appears there are two reference frames: ground and moving train, in the post #8.
The rotating wheel does circular motion in the train frame and it does cycloidal motion in the ground frame.

Where is the rotating reference frame?


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What has this to do with the theory of relativity?

In any complex motion scenario, you can arbitrarily assign reference frames at your choice.

I think the reason skeptics don't address the problem is that there isn't a problem.

Hans
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Old 23rd July 2018, 09:02 AM   #19
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Originally Posted by SDG View Post
You lost me.


I have no idea what you are saying here.


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Again as I recall one of the posters remarked one of the ways to break down the pendulum motion into approximations was to treat the pendulum as the rigid non-rotating form and then consider the rotation separately as just basic angular momentum or velocity. The two approximations combined should be a good overall approximation of the motion dynamics.

Again, the discussion seems to be centered on mathematical methods for modeling motion not specifically relativity.

The only mention of relativity that I saw was the claim that there should be a way to detect constant linear motion without external reference. Which is plainly deficient just on its face. If I'm in my car moving 5 MPH South relative to another car yet 5 MPH North relative to a third. What or which constant linear motion should one be able to detect without external reference? 5 MPH South, 5 MPH North, both which sum to 0 or any one or number of the multitude of other cars I'd be in constant linear motion relative to? The claim just represents a basic misunderstanding of how motion is defined in general.

Perhaps there is some other claim, something else you feel is at stake in regard to relativity. As noted by others you're going to have to try to clue us in there. As the basic claim you were making here, about that thread there, is "nobody is defending relativity". Who needs to defend relativity if nothing is actually attacking relativity? As the discussion there seems to be centered on modeling motion it doesn't even look like those posters are perceiving a reason to defend relativity.

ETA
OH and a hint about the train example. The wheels only represent an external reference to the ground only with an external observation of the ground in relation to the wheels. Otherwise they could just be spinning freely indicative of no relative motion other than just their own.
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Old 23rd July 2018, 09:24 AM   #20
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I haven't looked at the thread in the other forum and have no intention of doing so. I am responding here to explain to SDG why he needs to be more precise when explaining what is at stake in that discussion.

Originally Posted by SDG View Post
What is at stake? The poster claims the experiment in the post #8 can detect linear straight motion without any signal from the outside. The relativity says this is not possible! If that experiment turns out to be true then the relativity as we know it is dead. This is what is at stake here.

There are at least two different ways to interpret the phrase I highlighted.

(1) If the highlighted phrase is taken to mean it is possible to distinguish geodesic "linear straight motion" from accelerated (that is, non-geodesic) motion, then the highlighted phrase is indeed possible and entirely consistent with Einstein's theories of relativity.

(2) If the highlighted phrase is taken to mean it is possible to distinguish one geodesic "linear straight motion" from other geodesic motions without referring to any non-local information such as a "signal from the outside", then the highlighted phrase is not possible according to relativity.

On the basis of what SDG has written, I cannot tell whether he is disagreeing with the basic fact of relativity stated in interpretation (1) or defending the basic fact of relativity stated in interpretation (2).
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Old 23rd July 2018, 09:29 AM   #21
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I'm staring to think that part of the confusion might be due to inertial and non-inertial reference frames. Since non-inertial frames can result in inertial forces those forces can be translated to motions which might represent just changes in motion.

The very basis of inertial navigation.

https://en.wikipedia.org/wiki/Inerti...igation_system
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Old 23rd July 2018, 10:22 AM   #22
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Originally Posted by MRC_Hans View Post
What has this to do with the theory of relativity?

In any complex motion scenario, you can arbitrarily assign reference frames at your choice.

I think the reason skeptics don't address the problem is that there isn't a problem.

Hans
Hans, you do not see the problem, that's fine.
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Old 23rd July 2018, 10:31 AM   #23
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Originally Posted by SDG View Post
What is at stake? The poster claims the experiment in the post #8 can detect linear straight motion without any signal from the outside. The relativity says this is not possible! If that experiment turns out to be true then the relativity as we know it is dead. This is what is at stake here.
Relativity is too well understood, and too well observed across too wide a range of observations, to be killed by this experiment. There is actually nothing at stake here. The most reasonable assumption is that the experiment is poorly formulated, and that nobody yet cares enough about it to try to fix it.

Someone who does care that much may come along, but even if they don't, there's still nothing at stake.

Is this your experiment we're talking about? Are you thinking you may have disproven relativity?
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Old 23rd July 2018, 10:46 AM   #24
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Originally Posted by W.D.Clinger View Post
I haven't looked at the thread in the other forum and have no intention of doing so. I am responding here to explain to SDG why he needs to be more precise when explaining what is at stake in that discussion.




There are at least two different ways to interpret the phrase I highlighted.

(1) If the highlighted phrase is taken to mean it is possible to distinguish geodesic "linear straight motion" from accelerated (that is, non-geodesic) motion, then the highlighted phrase is indeed possible and entirely consistent with Einstein's theories of relativity.

(2) If the highlighted phrase is taken to mean it is possible to distinguish one geodesic "linear straight motion" from other geodesic motions without referring to any non-local information such as a "signal from the outside", then the highlighted phrase is not possible according to relativity.

On the basis of what SDG has written, I cannot tell whether he is disagreeing with the basic fact of relativity stated in interpretation (1) or defending the basic fact of relativity stated in interpretation (2).

Let us imagine a big spaceship with a big long cargo space floating (not accelerating) in the intergalactic space.
There is 'a train car' in the cargo space flying/floating at constant velocity as described in the other thread.
There is the wheel as described in the other thread rotating as described over there in that thread.
If the big spaceship frame is like 'the ground reference frame' and 'the train car reference frame' is like the moving frame so the math should apply here as well for this scenario.
It appears to me this is the case (2).

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Old 23rd July 2018, 10:51 AM   #25
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Originally Posted by theprestige View Post
Relativity is too well understood, and too well observed across too wide a range of observations, to be killed by this experiment. There is actually nothing at stake here. The most reasonable assumption is that the experiment is poorly formulated, and that nobody yet cares enough about it to try to fix it.

Someone who does care that much may come along, but even if they don't, there's still nothing at stake.

Is this your experiment we're talking about? Are you thinking you may have disproven relativity?
Very proficient skeptic statement.
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Old 23rd July 2018, 11:14 AM   #26
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Originally Posted by SDG View Post
Very proficient skeptic statement. : )
Thanks! I also asked a question, though.
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Old 23rd July 2018, 11:49 AM   #27
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it's a complete non-discussion at naked, the guy just does not want to make approximations, fine, he will have to do the hard work, lost interest after his endless complaining
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Old 23rd July 2018, 12:29 PM   #28
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Originally Posted by tusenfem View Post
it's a complete non-discussion at naked, the guy just does not want to make approximations, fine, he will have to do the hard work, lost interest after his endless complaining


What are you talking about?
What approximation he is supposed to do?
If I understand correctly the argument is that the balls will 'absorb' different amount of energy into the rotational kinetic energy at different points of the cycloid. This would lead to different velocity on the cycloid as compared to what is expected by the relativity.

When the wheel acceleration is observed from the moving reference frame then every point is supposed to obtain the same rotional kinetic energy for every single point on the circle trajectory.
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Old 23rd July 2018, 12:32 PM   #29
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Train motion relative to rails, wheel motion relative to train, The Theory Of Relativity has to be involved.
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Old 23rd July 2018, 12:37 PM   #30
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Originally Posted by SDG View Post
Let us imagine a big spaceship with a big long cargo space floating (not accelerating) in the intergalactic space.
There is 'a train car' in the cargo space flying/floating at constant velocity as described in the other thread.
There is the wheel as described in the other thread rotating as described over there in that thread.
If the big spaceship frame is like 'the ground reference frame' and 'the train car reference frame' is like the moving frame so the math should apply here as well for this scenario.
It appears to me this is the case (2).
I found that other thread/discussion to be quite confusing.

How about you write up what you consider to be the challenge to relativity here, without reference to that? If you do that, you can directly address any ambiguity or misunderstanding, and ISF members will know exactly what you mean.
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Old 24th July 2018, 05:04 AM   #31
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Originally Posted by tusenfem View Post
it's a complete non-discussion at naked, the guy just does not want to make approximations, fine, he will have to do the hard work, lost interest after his endless complaining


Is his complaint about the wrong pendulum conservation of energy equation justified?


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Old 24th July 2018, 05:10 AM   #32
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Originally Posted by JeanTate View Post
I found that other thread/discussion to be quite confusing.



How about you write up what you consider to be the challenge to relativity here, without reference to that? If you do that, you can directly address any ambiguity or misunderstanding, and ISF members will know exactly what you mean.


My post #28 is a summary of my understanding of the issue. If that doesn't help then I can't do any better.

I am quickly building a picture of this forum.
Leaders here do not understand cycloids.


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Old 24th July 2018, 07:41 AM   #33
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Originally Posted by SDG View Post
My post #28 is a summary of my understanding of the issue. If that doesn't help then I can't do any better.
I'm sorry to hear that.

If it's so, then I guess what you consider to be a serious problem with relativity will remain entirely with you.

Quote:
I am quickly building a picture of this forum.
Leaders here do not understand cycloids.
Have you been able to estimate how many ISF members, who post in threads in this section, are (or have been) teachers? University lecturers? How many do you think have a BSc, an MSc, a PhD? What fields of study do you think they specialized in? How many of those with an MSc or PhD in physics (or related field, such as astrophysics) do you think needed to address one aspect or other of relativity, as part of the work they did on their thesis? How about (advanced) degrees in other fields, such as engineering or mathematics (where an intimate understanding of cycloids is required), how many ISF members do you think there are with such degrees? In terms of their day-to-day work (or former, if retired), how many ISF members do you think need to deal with one aspect of relativity or another? How about cycloids (and related analytic forms)? And so on.

If you do not have at least some appreciation for answers to at least some of those questions, would it be a rational thing to conclude that you, SDG, do not understand your audience?
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Old 24th July 2018, 07:43 AM   #34
Roboramma
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Originally Posted by SDG View Post
My post #28 is a summary of my understanding of the issue. If that doesn't help then I can't do any better.
Given that post #28 was in response to someone who specifically said he wasn't going to look at the other forum and your summary included the phrase "as described in the other thread", I don't think your summary is adequate.

If you are incapable of doing better that's fine, but don't expect much discussion to ensue.

If you don't understand the issue well enough to describe it in your own words, maybe your understanding of what you consider to be a problem is also lacking.
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Old 24th July 2018, 07:47 AM   #35
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Originally Posted by SDG View Post
Is his complaint about the wrong pendulum conservation of energy equation justified?
Who cares?

Unless "he" is you, and until you post something here that's concise and conveys the key point unambiguously (without lots of unrelated stuff, for example), why should anyone who posts in this part of ISF care?

For avoidance of doubt, the internet is replete with material that appears to be physics, but contains misunderstandings and errors, of many kinds, at many levels. If an ISF member is interested in discussing something in one of those places, fair enough; if no one is interested, why kick up a fuss?

tl;dr: life is too short to spend on what is almost certainly confused thinking (at best).
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Old 24th July 2018, 08:04 AM   #36
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SDG, is the relativity-breaking cycloid claim your claim?
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Old 24th July 2018, 08:23 AM   #37
The Man
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Originally Posted by SDG View Post
What are you talking about?
What approximation he is supposed to do?
If I understand correctly the argument is that the balls will 'absorb' different amount of energy into the rotational kinetic energy at different points of the cycloid. This would lead to different velocity on the cycloid as compared to what is expected by the relativity.
OK, what is "expected by the relativity" and what is the "different velocity on the cycloid"?

Again this seems to be a problem of mixing frames. Again breaking the motion down to rotational and lateral motions separately (as recommended by one of the posters on that thread) helps one to keep their frames straight. In a reference frame rotating with the wheel the wheel would just move laterally with no rotation and have some particular kinetic energy based on that motion.


Originally Posted by SDG View Post
When the wheel acceleration is observed from the moving reference frame then every point is supposed to obtain the same rational kinetic energy for every single point on the circle trajectory.
I expect by "the moving reference frame" you mean co-moving with just the lateral motion of the wheel. In that frame the wheel would simply rotate. It is basic rotational mechanics that dictates any equal portion of the wheel with equal mass and centered equal radius from the axis of rotation will have equal rotational kinetic energy, not relativity itself. So the wheel would have some total rotational kinetic energy in that frame.

In a frame neither co-moving laterally nor rationally with the wheel, the wheel would have a combination of such motions and kinetic energy. How or how much of that energy it could transfer to something else in that frame would depend on the dynamics of the interaction as the rotational motion has vector components that oppose, add to or have no effect on the lateral motion depending on the relative point of interaction with the wheel. Again really all just basic mechanics of motion stuff but just in a complex application. Again the real use of relativity here is to break down the motion to the lateral and rotational motion frames to reduce the complexity and chance to confuse frames and motions.
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Old 24th July 2018, 12:24 PM   #38
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Originally Posted by SDG View Post
My post #28 is a summary of my understanding of the issue. If that doesn't help then I can't do any better.

I am quickly building a picture of this forum.
Leaders here do not understand cycloids.


Sent from my iPhone using Tapatalk

As a cyclist, I'm offended. The cycloidal motion in one complete rotation of the wheel as viewed from the ground plane will be identical to previous wheel rotations and future wheel rotations. Therefore, you will not be able to detect a constant linear motion.

Last edited by Elagabalus; 24th July 2018 at 12:27 PM.
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Old 24th July 2018, 01:09 PM   #39
MRC_Hans
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Originally Posted by SDG View Post
My post #28 is a summary of my understanding of the issue. If that doesn't help then I can't do any better.
Well, it is OK if you don't understand the issue. Then you can't be expected to explain it.

Quote:
I am quickly building a picture of this forum.
Leaders here do not understand cycloids.
You are quickly building a reputation of someone who jumps to conclusions.

Hans
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Old 24th July 2018, 02:19 PM   #40
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Originally Posted by MRC_Hans View Post
Well, it is OK if you don't understand the issue. Then you can't be expected to explain it.



You are quickly building a reputation of someone who jumps to conclusions.

Hans

I think one of the points SDG is missing (as well as perhaps the original poster on the other thread) is that if you can observe the cycloidal motion of some point on the wheel then you can already directly observe the lateral motion of the wheel. The rotational motion just becomes superfluous. Were the train, bike, car or whatever to lock its brakes and skid on ice or say hydroplane the rotation of the wheel just stops but the lateral motion of the wheel continues. If you can't directly observe any lateral motion of the wheel then there is no cycloidal motion you can observe but just rotational motion of points on the wheel.
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