Conservation of angular momentum was already mentioned in Newton's publication "Principia", nearly 340 years ago. No experimental observation has ever shown a violation of this law, even those made in the realm of Quantum Mechanics or General Relativity.
Yet, for nearly 10 years now, John Mandlbaur has been claiming in his peer-rejected publication which he qualifies as "the perfectly well written and undefeated proof of my historic discovery" that angular momentum is not conserved. He claims that a "ball on a string" (which we commonly call a conical pendulum) is enough to prove that it is angular energy" (which we commonly call rotational kinetic energy) that is conserved, not angular momentum.
For 10 years people attempted to explain him that the correct statement of the law is that "angular momentum is conserved if the external torque on the system is zero", but he refuses to understand that his yo-yo is undergoing a non negligible torque due to the air drag which increases quadratically with the speed of the bob. He claimed that no experiment with "a ball on a string" has ever supported conservation of momentum. In order to prove him wrong (one more time), the experiment of "a ball on a string" has been performed and video recorded, and measurements made directly on the video to prove that there is no fudge in the numbers. With no surprise, the experiment properly done proves that rotational kinetic energy is not conserved, and that supports the fact that angular momentum is conserved.
The experiment with "a ball on a string" properly done is available here:
https://youtu.be/abuPJesWQRY
In addition, an experiment of a rotational collisions is available here:
https://youtu.be/RE-6s1B-lc8
By direct calculation. It suffices to write the Lagrangian and show that the action is invariant under rotations of the coordinates and that this leads to conserved charges, which can be identified with the components of angular momentum. This is a standard exercise in any course on mechanics.
Of course, if one does impose a torque, then angular momentum isn't conserved.
Of course, but I doubt that John Mandlbaur could be able to understand Lagrangian mechanics. If you don't know who he is, take a look at this video that gives a short presentation before experimentally proving him wrong:
https://youtu.be/RE-6s1B-lc8
Then it just doesn't make sense granting him-or anyone else like him-the attention they actually are after. Such people are, just, looking for clicks and it's important not to give them clicks.
If that was possible then perpetual motion devices would've worked by now.
The fact that angular momentum is not conserved is the reason that perpetual motion is not possible.
If it were possible to pull in a ball on a string to 1/10th from an initial spin of 2 rps, and achieve 12000 rpm as predicted, then the massive increase in energy from what a five year old can do, would be free energy.
John Mandlbaur
Nope, the energy would not be free, the energy simply comes from the work done by pulling the string, as I have already told you and explained here: https://youtu.be/A2evqQ6nWoQ
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