The conserved quantity arising from a rotational invariance. Combine with rotational-dynamics for the classical mechanics approach and quantum-mechanics for the QM interpretation

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6answers
843 views

Why does the Earth rotate? [duplicate]

Possible Duplicate: Why does every thing spin? So why would the Earth, or any planet for that matter, rotate along an axis? I know of no force which could come into play here, so i assume ...
3
votes
1answer
698 views

Conservation of angular momentum for a nonrigid body

Question: The sun is not a rigid body but a hot ball of gas. The period of rotation varies from 37 days at the pole to 26 days at the equator. The mean radius of the sun is $7\times 10^8\text{ ...
3
votes
1answer
518 views

Equation that tells me the rpm and mass of a spinning disk needed to keep a second large mass stable using gyroscopic effects

I am trying to figure out how large of a mass and how quickly I need to spin said mass to keep a two-wheeled robot stable. Ideally, I am looking for a formula that relates m1=mass of robot, m2=mass of ...
4
votes
2answers
359 views

Interference of EM Waves with Orbital Angular Momentum

If you have two coherent collinear e-m beams of same frequency and polarization, but 180 degrees out of phase, they will destructively interfere. If you introduce orbital angular momentum of L=3 ...
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votes
6answers
8k views

Why are some galaxies flat?

What is the explanation for the flatness of some galaxies? (If it's due to their rotation then why they are rotating, why some other galaxies are not flat etc., I would like to hear a nice and ...
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1answer
395 views

Measuring the mass using angular velocities

I have 2 objects which are intially connected together, $O_1$ and $O_2$. When they are connected together, they have a rotation rate about their center of mass of $w_1$. $O_2$ is cleanly released from ...
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1answer
482 views

Simultaneously commuting set

How does one determine the members of an simultaneously commuting set (of operators)? For example, I have read that for orbital angular momentum, the set is {$H,L^2,L_z$}. How does one know that these ...
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2answers
2k views

Why are our planets in the solar system all on the same disc/plane/layer?

I always see pictures of the solar system where our sun is in the middle and the planets surround the sun. All these planets move on orbits on the same layer. Why?
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vote
1answer
367 views

Where are the centers of mass for a baseball bat vs. a cricket bat?

My friend and I were comparing the rightness of a cricket bat versus a baseball bat for general violence purposes. (Eg, rioting.) Where are the centers of mass for these two instruments? Which would ...
5
votes
3answers
686 views

confused about ball rolling and rotational energy

I was solving a practice test problem and it was just a conservation of energy problem where a spherical ball is falls from a height h to the ground such that $$mgh = \frac{1}{2}mv^2 + ...
3
votes
1answer
40 views

What determines a progenitor's fate as a spiral or elliptical?

I was thinking about my answer to Are the inner planets on planar orbits because there was more dust in the inner solar system (early on in planetary accretion)? - when it occurred to me that maybe I ...
13
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3answers
938 views

Where the angular momentum has gone?

I came across an interesting problem when I prepared for the preliminary exam on electromagnetism. Below is the problem in its original words: A metallic sphere of mass, $m$, and radius, $a$, ...
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1answer
902 views

Spinning wheel on rotating stool - why am I also affected even when the wheel axis is horizontal?

So I can point the axis of spin in one horizontal direction - and then move it in another direction (so it stays horizontal - like the picture below). And that still changes the direction of spin (on ...
5
votes
2answers
1k views

How is angular momentum conserved when a spinning top finally stops spinning?

Where does the top's angular momentum get transferred to? Does it very slightly change the angular momentum of the table, and then the angular momentum of the Earth?
4
votes
2answers
199 views

Where does a star's angular momentum go as its spin slows down?

So we know that stars slow down as they age. But total angular momentum must be conserved. Where does that angular momentum go? The dissipation of Earth's tides somehow transfers Earth's angular ...
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vote
2answers
185 views

Converting Angular Momentum?

I am aware of three apparently different forms of angular momentum: spin, orbital and macroscopic, like a spinning crystal or baseball. Can angular momentum be transferred or converted from one of ...
6
votes
3answers
492 views

How does Hubble's constant affect the Earth's orbit

If Hubble's constant is $2.33 \times 10^{-18} \text{ s}^{-1}$ and the earth orbits the sun with average distance of 150 million kilometers; Does that mean the earth's orbital radius increases ...
3
votes
4answers
335 views

N particles, will there be any rotation after a period of time or everything will collapse

This is in context of classical Newtonian physics. Consider a system of n different point mass particles. Initially all are spread around on one plane. No particle possess any velocity to begin with. ...
32
votes
5answers
2k views

Why does everything spin?

The origin of spin is some what a puzzle to me, everything spin from galaxies to planets to weather to electrons. Where has all the angular momentum come from? Why is it so natural? I was also ...
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2answers
2k views

maximum rotational speed

I am wondering if there is a limit to rotational speed of an object just like there is one for translation speed ? what are the implications of general relativity for rotating objects ?
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2answers
278 views

Clebsch-Gordan Identity

I'm trying to take advantage of a particular identity for the sum of the product of three Clebsch-Gordan coefficients, however, the present form of my equation is slightly different. Is there a ...
3
votes
1answer
149 views

generalizing spin rotations

I have a question about the relation: $\exp(-i \vec{\sigma} \cdot \hat{n}\phi/2) = \cos(\phi/2) - i \vec{\sigma} \cdot \hat{n} \sin(\phi/2)$. In my texts, I see $\phi\hat{n}$ always as c-numbers. My ...
5
votes
1answer
121 views

Sum of angular momentum of all electrons in a magnet

Can the sum of angular momentum of all rotating electrons in all the aligned atoms in a permanent magnet have a significant contribution to the macro angular momentum of the magnet? If yes, why does ...
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2answers
1k views

How does one experimentally determine chirality, helicity, spin and angular momentum?

If I've got an instance of a fundamental particle, how can I separate out the measurements of these three concepts? (I think) I understand the theory behind them, and why the particles in the ...
14
votes
4answers
2k views

Why does each celestial object spin on its own axis?

AFAIK all the celestial objects have a spin motion around its axis. What is the reason for this? If it must rotate by some theory, what decides it's direction and speed of rotation? Is there any ...
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vote
3answers
678 views

QM interpretation of Larmor precession

Typically when I think of a spin moment in an external field, I visualize it classically in terms of a magnetic moment precessing around the external field vector. Now how is this described quantum ...
14
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1answer
3k views

How to define angular momentum in other than three dimensions?

In classical mechanics with 3 space dimension the angular momentum is defined as $\mathbf{L} = \mathbf{r} \times \mathbf{p}$ In relativistic mechanics we have the 4-vectors $x^{\mu}$ and $p^{\mu}$, ...
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1answer
917 views

Modeling and Simulating Pendulum Motion

I've been having difficulty creating a mathematical model of a pendulum in my code. While there is plenty of info on general equations describing a the motion of a pendulum, I seem to be having ...
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votes
8answers
6k views

How do you explain spinning tops to a nine year old?

Why don't spinning tops fall over? (The young scientist version) My nine year old son asked me this very question when playing with his "Battle Strikers" set. Having studied Physics myself, I am very ...
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vote
1answer
340 views

resistance of a flywheel to change of angular momentum

I've got a flywheel with angular momentum $\vec L$. Now I'd like to change the orientation of $\vec L$ by an angle $φ$ (in degrees). How do I calculate the angular momentum $\vec M$ for that change?
5
votes
2answers
2k views

Relation between total orbital angular momentum and symmetry of the wavefunction

My question essentially revolves around multi-electron atoms and spectroscopic terms. I understand the idea that the total wavefunction for Fermions should be antisymmetric. Consider as an example, ...
7
votes
3answers
418 views

Are there planetary systems where the planes of orbits vary greatly?

Inspired by this question, are there any known planetary systems with largely varying planes of orbit? For example a system where two planets have perpendicular planes?
10
votes
4answers
682 views

Why do all the planets of the solar system orbit in roughly the same 2D plane?

Most images you see of the solar system are 2D and all planets orbit in the same plane. In a 3D view, are really all planets orbiting in similar planes? Is there a reason for this? I'd expect that ...
4
votes
1answer
368 views

Angular momentum in string theory

Since strings are extended objects, is all angular momentum in string theory essentially "orbital" angular momentum? Or is there still a kind of intrinsic angular momentum assigned to a string? ...
8
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2answers
779 views

Intrinsic angular momentum in classical mechanics

Please note, I am only interested in classical mechanics discussion on this. Please do not involve quantum mechanics. Inspired by this question: Is Angular Momentum truly fundamental? My question ...
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2answers
1k views

Mech stability through gyroscope

I recently read up about gyroscopes, angular momentum and mechs (the big Cockpit controlled robots) and was wondering if it would be possible to get a stable walking mech (only as example, not meant ...
1
vote
0answers
152 views

Will earth rotation be slowed down? [duplicate]

Possible Duplicate: Are tidal power plants slowing down Earth's rotation? Since we have various energy acquiring facilities that harvest energy from earth rotation. (e.g. wind, tidal ...
5
votes
1answer
699 views

Angular momentum and EM wave

Is there any sense in saying that circularly polarized EM waves have angular momentum?
2
votes
1answer
828 views

Does ABS cause a force that resists turning a car into a corner?

ABS systems work by allowing a tire to continue to rotate rather than "locking-up" (stop turning) due to loss of traction with the road surface. A rotating tire can influence the direction of the ...
3
votes
2answers
1k views

Dynamics of moment of inertia

I'd like to be able to determine the angular acceleration of a system of two rotating masses, which are connected so as to have a variable mechanical advantage between the two. My background with ...
2
votes
3answers
594 views

How long for a frictionless top to fall over?

We've previously discussed why it is that spinning tops do not fall over, see: Why don't spinning tops fall over? However, as the highest rated answer notes, the angular momentum of the spinning top ...
2
votes
2answers
515 views

Homework about spinning top [closed]

I have a top of unknown mass that has a moment of inertia $I=4\times 10^{-7} kg \cdot m^2$. A string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 ...
0
votes
1answer
209 views

Interaction of polarized beam to optical active substance

Kostyas question for angular momentum and half wave plates Half wave plate and angular momentum made me think a little bit. It took me some seconds to "swallow" the answer. :=) Then I started to ...
5
votes
2answers
637 views

Half wave plate and angular momentum

Given: A half wave plate freely floating in space. Circularly polarized light, falling perpendicularly to it. The plate changes polarisation of the beam to the opposite one. Therefore it ...
2
votes
3answers
1k views

Could life survive a pole shift caused by an asteroid collision?

Could life on earth survive a large pole shift caused by an asteroid collision? I became aware that there are people who believe that the earth's pole suddenly shifts. That is, its rotational ...
8
votes
2answers
452 views

Addition of Angular Momementa in deeply bound situations, proton spin crisis

In Landau and Lipshitz's introductory book on Quanum Mechanics, "Quantum Mechanics Non-Relativistic Theory, Third Edition: Volume 3", chapter XIV (page 433 in the edition on Amazon) is "Addition of ...
7
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5answers
13k views

Why does a ballerina speed up when she pulls in her arms?

My friend thinks it's because she has less air resistance but I'm not sure.
9
votes
1answer
1k views

Why do galaxies and water going down a plug hole spin?

We all experience things spinning, whether it's water down a drain, the earth on its axis, planets round the sun, or stars in a galaxy - even electrons round an atom. But why is spin so common in ...
22
votes
6answers
1k views

Rotation angle of a giant lily when a child crawls on its rim

Below is a picture of Giant Water Lily. Scientific Name: Victoria Amazonica. Leaves of some of these could be as big as 3 m diameter and carry a weight of 45kg spread evenly and can support a child. ...
10
votes
5answers
1k views

Why does a curling rock curl?

In the game of curling, players "curl" a granite "rock" (of precise size and roughly a flattened cylinder) down a "sheet" of ice towards a target; the "rock" will curve in its path in the direction of ...