Comments about "Angular_momentum" in Wikipedia

This document contains comments about the article Angular_momentum in Wikipedia
In the last paragraph I explain my own opinion.




The article starts with the following sentence.
In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum.
By itself, this sentence does not say anything.
It is an important quantity in physics because it is a conserved quantity—the total angular momentum of a closed system remains constant.
What does that mean? Does that implies that a spinning wheel always spins?

1. In classical mechanics

1.1 Definition

1.1.1 Orbital angular momentum in two dimensions

1.1.2 Scalar—angular momentum from Lagrangian mechanics

1.1.3 Orbital angular momentum in three dimensions

1.2 Discussion

1.2.1 Angular momentum and torque

1.3 Conservation of angular momentum

The conservation of angular momentum explains the angular acceleration of an ice skater as she brings her arms and legs close to the vertical axis of rotation.
Experiments show that the rotating speed of an rotating object is a function of the shape of a rotating object. This should be the start of any explanation and the bassis for the laws that describe this behaviour.

1.4 Angular momentum in orbital mechanics

1.5 Solid bodies

1.6 Collection of particles

1.6.1 Center of mass

1.6.2 Simplifications Single particle Fixed center of mass

2 Angular momentum (modern definition)

3 In quantum mechanics

3.1 Spin, orbital, and total angular momentum

3.2 Quantization

3.3 Uncertainty

It should be mentioned that within the evolution of physical processes there exist no uncertainty. As such uncertainty is not an inherent part of our understanding nor of any physical law. Uncertainty is only part of human capabilities to measure anything exactly.
Scalars (counts) can be measured exactly. Positions can be measured exactly if they are related to object at rest in a reference frame. Velocities of objects can not be measured exactly.
However, the Heisenberg uncertainty principle tells us that it is not possible for all six of these quantities to be known simultaneously with arbitrary precision.
This has nothing to do with any principle. Human capabilities have their limitations.

3.4 Total angular momentum as generator of rotations

4 In electrodynamics

5 In optics

6 History

6.1 The Law of Areas

6.1.1 Newton's derivation

6.1.2 Conservation of angular momentum in the Law of Areas

6.2 After Newton

7. See also

Following is a list with "Comments in Wikipedia" about related subjects

Reflection 1 - Understanding

The central theme of my homepage is about understanding. The more I try to understand - the evolution of the universe - the more I realise how important experiments are. Experiments are the bases of our understand. In fact you can learn something from each new experiment.
The central reason specific this review about "Angular_momentum" is the review of the book "Synchronicity: Epic Quest to understand the Quantum Nature of Cause and effect" in Nature. See: When quantum physics met psychiatry . In that article 'Conservation of angular momemtum' is also discussed. This immediate makes a link to the behaviour rotating objects, specific in relation to the radius of an object. Experiments show when the radius becomes shorter the (rotating) speed becomes longer. The question is how do you explain this. The solution is to impose The Law of Conservation of Energy which states that the total amount of energy in a closed environment (my understanding) is always constant. The question is can you use that law to understand the bahaviour of a spinning object.
From a more philosophical perspective what you do: you replace something that you don't fully understand by something else that you also don't fully understand.

Reflection 2 - (Energy) Conservation Laws

Conservation Laws are not absolute.
Newton's Third Law which states that any action always involves a reaction does not say much. It is better to improve our understanding by means of experiments. Consider the next:
You kick against a ball and the ball starts to move. As a result the ball moves through space, touches the surface and after a certain distance comes to a hold.
Technical speaking when you kick the ball, you apply a force against the ball. At that same moment there is a transport of energy between you and the ball. (The total amount of energy stays the same).
After touching the surface the speed of the ball will decrease and the ball will stop, because of friction. During that period kinetic energy is exchanged with heat. A much more difficult question to answer what is period and what is this distance. To answer this question is only possible under very controlled situations. That means conservation laws are not very helpfull if you only want to study one specific type of energy.

The same is even more true when possible conservation rules of individual particles are studied. Spicific in relation to entanglement.

Reflection 3


If you want to give a comment you can use the following form Comment form
Created: 7 September 2020

Go Back to Wikipedia Comments in Wikipedia documents
Back to my home page Index