Debunk this "unorthodox physicist", please

[Schnitte]

I’ve come across this website of a self-appointed researcher who claims that the law of preservation of angular momentum is wrong. He penned a large number of (poorly written) papers (and published them on his website, together with the rejection letters from the journals to which he submitted them) presenting his views. In a nutshell, they all boil down to the following arguments (at least that’s how I understand them; I’m paraphrasing here):

In the classic ball-on-a-string experiment that is used in high schools to illustrate angular momentum (ball rotates on a string, then the length of the string and thereby the radius of rotation is reduced, which accelerates the angular velocity of the ball), accepted physics say that angular velocity is inversely proportional to the square of the radius. So if you start with a given radius and a rotation of (his example) two revolutions per second, and then reduce the radius to a tenth of the initial radius, then the ball should now rotate at two hundred revolutions per second, or 12,000 revolutions per minute, which is more than what one observes in these experiments. Additionally, he appears to be making a conservation of energy argument: When the ball is now going at 200 rather than 2 revolutions per second, with a radius (and hence perimeter) of its circular orbit now a tenth of what it was before, then the non-angular velocity (in metres per second) has increased by a factor of ten. That means kinetic energy (E = 0.5mv²) also increases, violating the law of conservation of energy.

Surely this guy is wrong somewhere, but I can’t spot where exactly, and I’d love to know why - not for online debating purposes but out of a layman’s curiosity.

[LowSignalToNoise]

moment of inertia:
a quantity expressing a body’s tendency to resist angular acceleration. It is the sum of the products of the mass of each particle in the body with the square of its distance from the axis of rotation.

https://en.wikipedia.org/wiki/Moment_of_inertia

Linear momentum is mass times velocity.

Angular momentum is moment of inertia times angular velocity.

Guessing this “unorthodox physicist” is doing something with mass times angular velocity. And/or thinking the ball on the string has zero size (i.e. is a point mass.)

[rat_avatar]

1. For the same reason firing a shotgun doesn’t end in the same result as being fired at by a shotgun. (physical problem even with intro level math)
2. He is using a formula that uses the cross product and not the exterior product. (not using anything modern)
3. He is using formulas from an intro to physics textbook that apply to point masses. (note his cites)
4. His theory would be using tensors if it was modern, or even likely to be correct. (see 2&3)

Basic *‘My first physics coursesub[/sub]’ *mistakes really.

[Quercus]

He is of course, wrong about conservation of momentum (really, he thinks nobody else could have noticed this stuff?)

Now, it is true that with a ball rotating on a string, if it ends up in a smaller orbit with the same angular momentum, the ball has more energy. But that’s because by pulling on the string to shrink the orbit, you’ve added energy to the ball. Since the force is along the line from the center point of the rotation, you’re not changing the angular momentum, but that doesn’t mean the energy isn’t changed.

I’m not going to bother reading the links to see how he’s misrepresenting the experimental data, except to point out that yes, 12,000 rpm sounds like a lot compared to 2 revolutions per second, but that’s why dishonest people shift units without warning.

[Chronos]

If you do the actual experiment, then you’re likely to get significant air drag for something moving that fast, and so no, the resulting speed won’t be quite as high as you would predict if you neglected air resistance. Do it in a vacuum, though, and mitigate other sources of friction as much as possible, and you will get an answer very close to what’s predicted by conservation of angular momentum.

And yes, if you shorten the string, of course the energy of the system will increase. That’s exactly what you would expect to happen, when you add energy to a system. You’ll need to exert a force on the string to pull the weight in, and you need to exert it over some distance, so you’re doing work (which is to say, adding energy)

[Chronos]

Oh, to address another situation that students sometimes notice: Suppose that we’re not adding energy to shorten the string. Suppose instead that the string is shortening itself, by wrapping around a spool or shaft. Why isn’t that a problem? There, the answer is that the string is not completely radial: It’s shifted by some small angle backwards, and so there’s some component of the tension force that’s pulling back on the ball. In that case, the string is exerting a torque on the mass, with the net effect that angular momentum of the system is not conserved (because it’s transferred to whatever is holding the spool in place), but the energy is.

[rat_avatar]

Drag doesn’t need to even be involved,

Note how he is using the formula for a point particle, “L = rp sin θ”

Yet there is nothing even close to a derivative when he changes the radius?

http://www.baur-research.com/Physics/MPS.pdf

He simply doesn’t understand the basic math here.

[rat_avatar]

Looking through the book it is quite clear he is using an example of an ice-skater, which is typically simplified to the concept of a cylinder rotating around it’s own center.

This example is given because it allows the math to ignore torque to simplify the problem. This assumption will not work with a yo-yo which doesn’t have a mass that is centered around the point of rotation.

[Chronos]

Ice skaters aren’t simplified to cylinders, and even if they were, that would be irrelevant to the question of whether they have any torque.

[rat_avatar]

As it is not legal I will not cite the text book. (OK I am not looking at the 2nd edition)

But you are right in on aspect the the total angular momentum of the system is a conserved quantity ONLY if there is zero net external torque.

Simply watch his video of his “experiment” and how he is twirling the pen to get the yo-yo to wrap around, which is adding net external torque

The claim just has so many problems it is hard to point them all out.

[rat_avatar]

OK. To be clear this guy is right on one point but his conclusions are wrong.

With this demonstration:

Orbiter

1. If the string is gradually lengthened by letting it out through the hole.
   [ul]
   [li]Energy changes, Angular momentum centered on post remains the same.[/li][/ul]

2. If the string is gradually shortned by pulling it in through the hole.
   [ul]
   [li]Energy is increased, Angular momentum centered on post changes.[/li][/ul]

3. If you perform the same experiment, allowing the string to wrap around the post like a tetherball:
   [ul]
   [li]Energy is constant, Angular momentum centered on post changes.[/li][/ul]

While this demonstration is never offered as proof of the conservation of momentum, but merely as an example here is why.

#2 and #3 The tension force points towards contact point, resulting in a non-zero torque; thus angular momentum about central point is not constant.
#2 Pulling in on the string is performing “work” which adds energy to the system.

It seems the initial error the maintainer of this site committed is assuming that a tool that Newton was describe as using for conceptualization a problem was the proof and the only proof.

The issues surrounding flaws in the experiment and the implementation of an experiment explain his confusion. But in general exclaiming you have proven well tested physics wrong by using introductory Physics textbooks won’t typically end in you winning any awards. In this case the key is keeping torque about central point at zero.

Had he calculated an increasing orbit with a string coming out of a tube the error bars would have been closer. But these basic formula are also quite dated at this time and have been replaced with much better models.

[Jackmannii]

His web page claims he has not even gotten to peer review at a journal but the rejection letters he published contradict him. My favorite succinct rejection:

*"To be publishable in this journal, articles must be of high quality and scientific interest, and be recognised as an important contribution to the literature.

Your Paper has been assessed and has been found not to meet these criteria."*

Ouch.

[Schnitte]

@Chronos

If you do the actual experiment, then you’re likely to get significant air drag for something moving that fast, and so no, the resulting speed won’t be quite as high as you would predict if you neglected air resistance. Do it in a vacuum, though, and mitigate other sources of friction as much as possible, and you will get an answer very close to what’s predicted by conservation of angular momentum.

And yes, if you shorten the string, of course the energy of the system will increase. That’s exactly what you would expect to happen, when you add energy to a system. You’ll need to exert a force on the string to pull the weight in, and you need to exert it over some distance, so you’re doing work (which is to say, adding energy)

Ah, so the answer is: With respect to the first argument, he actually would get to 12,000 rpm in his scenario if friction were eliminated, and to the second argument that, as he reduces the radius, he is adding energy to the system from the outside? Thanks, that’s precisely the kind of succint debunking I was hoping for!

[Chronos]

That sounds to me like he’s never gotten to peer review. When you submit to a journal, the first step is that the editors look it over to weed out the obvious crackpots, cranks, and idiots, and then if it passes that first check, they send it out to a few reputable scientists working in the same field to give it a more detailed look. It’s that second step that’s referred to as peer review.

[Riemann]

@Chronos

That sounds to me like he’s never gotten to peer review. When you submit to a journal, the first step is that the editors look it over to weed out the obvious crackpots, cranks, and idiots, and then if it passes that first check, they send it out to a few reputable scientists working in the same field to give it a more detailed look. It’s that second step that’s referred to as peer review.

Yes, peer reviewers are an unpaid pool of experienced and busy scientists. They would look askance at any journal editor who didn’t filter out nonsense like this. A lot of scientists get sent stuff like this direct from cranks anyway.

[rat_avatar]

While this video is really a Tensor Calculus tutorial, he will go over a more realistic way to work with angular momentum.

Tensor Calculus For Physics Majors 005| Diagonalizing 2nd Rank Tensors

Note the work to even calculate that the direction of angular momentum. If you understand tensors and calculus it isn’t that overwhelming besides being tedious, but to show this isn’t cherry picking, here is another example of:

“Calculus 3: Tensors (17 of 45) The Inertia Tensor: A Simple Example”

Calculus 3: Tensors (17 of 45) The Inertia Tensor: A Simple Example

Both of those are basic examples but any “proof” that would demonstrate that momentum, energy, or angular momentum would look similar to that. Once again these expansions are tedious but not difficult.

*If a system experiences no torque, then its angular momentum is conserved. *proof would look closer to something like this:

Torque = dL/dt
L = Iω
p = mv

The angular momentum vector L =

/ L[sub]1[/sub]
| L[sub]2[/sub] |
\ L[sub]3[/sub] /

ω =
/ ω[sub]1[/sub]
| ω[sub]2[/sub] |
\ ω[sub]3[/sub] /

I[sub]1[/sub] = ∫ ρ |r[sub]1[/sub]|[sup]2[/sup]dτ
I[sub]2[/sub] = ∫ ρ |r[sub]2[/sub]|[sup]2[/sup]dτ
I[sub]3[/sub] = ∫ ρ |r[sub]3[/sub]|[sup]2[/sup]dτ

Where matrix I =

/ I[sub]1[/sub] 0 0
| 0 I[sub]2[/sub] 0 |
\ 0 0 I[sub]3[/sub] /

The intertia tensor Ι =

/ L[sub]11[/sub] L[sub]12[/sub] L[sub]13[/sub]
| L[sub]21[/sub] L[sub]22[/sub] L[sub]23[/sub] |
\ L[sub]31[/sub] L[sub]32[/sub] L[sub]33[/sub] /

Where:
Ι[sub]ij[/sub] = ∫ ρ(δ[sub]ij[/sub]∑[sub]k[/sub]x[sub]k[/sub][sup]2[/sup] − x[sub]i[/sub]x[sub]k[/sub])dτ

Which is not a proof, because I gave up on the formatting so it is just some basic ascii art to help show what basic matrix and tensor actions look like (don’t grade me too hard, it’s hard to do that in SDMB)

Angular momentum is a *(pseudo)*vector quantity, and none of his papers even have a single vector.

I would hope Riemann and Cronos wouldn’t waste their time on what that site offered, it is too hard to get peer reviewed to waste that kind of time.

If you are curious on why his math is wrong this is a hard forum to show but I encourage you to learn. Vector and matrix math is honestly insanely useful in the real world. We have computers which will protect you from a lot of the really boring expansions now too.

[Mandlbaur]

@LowSignalToNoise

moment of inertia:
a quantity expressing a body’s tendency to resist angular acceleration. It is the sum of the products of the mass of each particle in the body with the square of its distance from the axis of rotation.

https://en.wikipedia.org/wiki/Moment_of_inertia

Linear momentum is mass times velocity.

Angular momentum is moment of inertia times angular velocity.

Guessing this “unorthodox physicist” is doing something with mass times angular velocity. And/or thinking the ball on the string has zero size (i.e. is a point mass.)

L = r x p. That is the original definition. Newton’s concept of a point mass is perfectly validly applied to a ball on a string and has been done so by physicists for three hundred years. Stop guessing and rather go and read my work.

[Mandlbaur]

@rat_avatar

1. For the same reason firing a shotgun doesn’t end in the same result as being fired at by a shotgun. (physical problem even with intro level math)
2. He is using a formula that uses the cross product and not the exterior product. (not using anything modern)
3. He is using formulas from an intro to physics textbook that apply to point masses. (note his cites)
4. His theory would be using tensors if it was modern, or even likely to be correct. (see 2&3)

Basic *‘My first physics coursesub[/sub]’ *mistakes really.

1. Absolute nonsense.
2. Does “modern” mathematics for this system give a different result? This is also nonsense.
3. I am using my first year university physics text book and Newton’s concept of a point mass applied to a ball on a string are perfectly valid. More nonsense.
4. That is the most ridiculous claim I have ever heard in my life. Newton’s work which is far from modern, must be wrong by your nonsensical thinking.

[Mandlbaur]

@Quercus

He is of course, wrong about conservation of momentum (really, he thinks nobody else could have noticed this stuff?)

Now, it is true that with a ball rotating on a string, if it ends up in a smaller orbit with the same angular momentum, the ball has more energy. But that’s because by pulling on the string to shrink the orbit, you’ve added energy to the ball. Since the force is along the line from the center point of the rotation, you’re not changing the angular momentum, but that doesn’t mean the energy isn’t changed.

I’m not going to bother reading the links to see how he’s misrepresenting the experimental data, except to point out that yes, 12,000 rpm sounds like a lot compared to 2 revolutions per second, but that’s why dishonest people shift units without warning.

You immediately announce your prejudice and present ad hominem attack. What I “think” is not within your realm of knowledge.

The professor pulling on the string slightly harder than he was already pulling cannot affect the angular energy because centripetal force cannot apply torque as you have agreed. Angular energy is rotational kinetic energy, except that it is conserved instead of angular momentum. We know that angular energy is the sum of the work done by torque. Centripetal force applies no torque and therefore cannot affect the angular energy. Much like you mistakenly claim that it cannot affect the angular momentum, the reality is that it cannot affect the angular energy. Since angular momentum is defined as L = r x p, and centripetal force can affect the radius, centripetal force can have a direct affect on the angular momentum. Our thinking has been mistaken here.

How can you claim I am “misrepresenting” something if you refuse to address it? That is just false ad hominem attack.

12000 rpm is not a lot, it is the engine speed of a formula one race car on full throttle at 300 km/hr. This is massively incongruent with reality. The reason I shift from rps to rpm is because anybody who has ever driven a car has a concept of just how fast 12000 rpm is. Nobody has any idea how fast 200 rps is because they have nothing to relate to. This is not dishonest as you further your ad hominem with false nonsensical accusations. It is practical.

[Mandlbaur]

@Chronos

If you do the actual experiment, then you’re likely to get significant air drag for something moving that fast, and so no, the resulting speed won’t be quite as high as you would predict if you neglected air resistance. Do it in a vacuum, though, and mitigate other sources of friction as much as possible, and you will get an answer very close to what’s predicted by conservation of angular momentum.

And yes, if you shorten the string, of course the energy of the system will increase. That’s exactly what you would expect to happen, when you add energy to a system. You’ll need to exert a force on the string to pull the weight in, and you need to exert it over some distance, so you’re doing work (which is to say, adding energy)

For three hundred years, physicists have taught us that a ball on a string demonstration using an ad hoc mass and a random thread conducted in the bare hands of a professor in the open air will conserve angular momentum and that friction and hand wobble and gravity will have a negligible affect on the results.

Your claim that it will conserve angular momentum in a vacuum is speculation. Back up your claim with evidence or retract it because it is nonsense.

If we measure a ball on a string demonstration, without yanking on it, then it confirms with great accuracy that angular energy is conserved and angular momentum changes as the radius changes like it is defined to do (L = r x p).