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# Questions tagged [angular-momentum]

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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### How to understand zero elements in CG coefficient table?

I understand the standard theory of angular momentum and the reps. of SU(2). I found there are some zero elements in CG coefficient table. I can derive them by using the recurrence relations between ...
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### How much should the disk/wheel spin for gyroscopic-precession to take place? Is there a threshold?

Suppose we have a spinning gyroscope whose disk is of mass $m$, spinning at angular velocity $\omega$, and attached to a rod of length $r$. The precession of the gyroscope around the $z$-axis will be ...
1 vote
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### Does angular momentum of rotating body depend on its position?

This question might be silly. But angular momentum $\vec{L} = \vec{r} \times \vec{p}$. It always confuses me whether or not angular momentum depends on the origin because the position vector does ...
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### How do we argue that there are only integer-spaced $m$ values for angular momentum?

I am following the usual development using ladder operators (in Ballentine Chapter 7) for the angular momentum spectrum (for the joint eigenbasis $|j,m \rangle$ of $J^2$ and $J_z$) and I am satisfied ...
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### Does a rotating body resist acceleration in a direction that is perpendicular to the direction of the rotation of the body?

I would like to know if a rotating body resists acceleration in a direction that is perpendicular to the direction of the rotation of the body. Say for example there is a bicycle wheel with a tire on ...
1 vote
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### Gyrating proton near magnetic pole of the Earth

Imagine a proton from space which approaches the magnetic pole in the Northern hemisphere of the Earth. The proton spirals around the magnetic field lines. The $\vec{B}$-field is stronger near the ...
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### Angular distribution of two-body decay with orbital angular momentum

I'm currently studying the two-body decay where a particle (Be) with spin-1 decays into a pion (spin-0) and spin-1 particle $X$. The system is prepared so that the Be is polarized with a spin ...
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### Why dimension units of radius is not $\rm m/rad$ or $\rm cm/rad$? [duplicate]

Radius is not a just simple size or length between the two points. The radius shows the connection of linear and angular values. Something must indicate the information about a perpendicularity of the ...
1 vote
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### Torque on a rotating axle [closed]

The problem is from the book Classical Mechanics by David Morin. Here's my attempt One of the principal axes will be along the rod ($\hat x_1$) and other two will be passing through the center ...
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### $J=1/2$ and $J=3/2$ Baryons with $uds$ quarks

Why are there two different $J = \frac{1}{2}$ baryons with quark content $uds$ (the $\Lambda_{0}$ and $\Sigma_{0}$) but only one $J = \frac{3}{2}$ baryon (the $Σ_{*,0}$) with the same quark content? I ...
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### Ladder Operators for Quantum Angular Momentum

Consider the operators \begin{equation*} \mathbf{J}^{2} = J_{x}J_{x}+J_{y}J_{y}+J_{z}J_{z} \end{equation*} where the $J_{i}$ are the generators of infinitesimal rotations. Choosing $\mathbf{J}^{2}$ to ...
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### Angular momentum of $N$ particles

I am reading Goldstein's Classical Mechanics book; I have difficulty understanding these lines. Why do the last two terms vanish? I am reading this and thinking $r'$ is a null vector, but the second ...
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### Shape of atomic orbitals

I am a physics bachelor student and currently learning quantum mechanics. In my course we derived the wave function for the hydrogen atom. I know that the quantum number L is connected with the shape ...
1 vote
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### Intrinsic Parity of the $𝐾^+$ Meson

Why it is not possible to determine intrinsic parity of the $𝐾^+$ mesons from the $𝐾^+ → 𝜋^+ 𝜋^0$ decay?
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### Confused about angular momentum conservation from deflection angle derivation

I have started going through A. Zee's "Einstien Gravity in Nutshell" after a good number of years away from studying physics (perhaps too many) and I have been stuck on a derivation that I ...
1 vote
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### Under what conditions can we assume action-reaction force pairs are along the line joining two objects (strong form of Newton's third law)?

In many circumstances we take it that when object $A$ applies a force on object $B$ and vice-versa, the two forces are central forces or along the line joining $A$ and $B$. This is used to derive ...
1 vote
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### Can a body rotate indefinitely about its axis in space?

Wondering if a rigid body can keep rotating about its axis with constant angular velocity without the application of any force or torque, to the object. Assuming that the object is not in influence of ...
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### Angular Momentum Operator

Can a system be in an eigenstate of the total angular momentum operator $L^2$ without being in an eigenstate of any of $L_x$, $L_y$, and $L_z$? What would such a state look like?
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### From where does the perpendicular component of force arise in this lever? Does it conflict with the strong form of Newton's third law?

Newton's third law states that for every force applied by object $A$ on object $B$, there is an equal an opposite force by object $B$ on object $A$. The strong form of Newton's third law states that ...