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
4,274 questions
-3 votes
0 answers
49 views
Problem in understanding the proof of Wigner-Eckart in Sakurai [closed]
In the book of sakurai Modern Quantum Mechanics they have this $$ \begin{aligned} & \sqrt{(j \mp m)(j \pm m+1)}\left\langle j_1 j_2 ; m_1 m_2 \mid j_1 j_2 ; j, m \pm 1\right\rangle \\ & =\sqrt{...
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2 votes
0 answers
53 views
Is angular momentum generator a tensor in the Poincare group?
According to Weinberg' QFT vol I, (2.4.8), the generator of angular momentum $J^{\rho\sigma}$ transform as $$U(\Lambda, a) J^{\rho \sigma} U^{-1}(\Lambda,a) =\Lambda_\mu^{\,\,\rho} \Lambda_\nu^{\,\,\...
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1 vote
0 answers
104 views
If the universe is spinning now was it spinning faster in the past to conserve angular momentum?
If the universe is rotating once every 500 billion years, as some researchers think, and angular momentum is conserved, then when the universe had a smaller radius was it spinning faster?
user550784
0 votes
2 answers
112 views
Veritasium rotating wheel angular momentum
In this Veritasium video, there is a rotating wheel attached to a rope hanging from ceiling by a rod connecting end of the rope to the center of the wheel. I understand that if you know that a priori ...
- 536
2 votes
1 answer
468 views
Can spin really be measured in an arbitrary direction?
If I am in the computational basis (given by unit vector ${z}$) and have a ket $|0\rangle$, and I have $\sigma = (\sigma_x, \sigma_y, \sigma_z)$, the Pauli matrices, then my ket is an eigenfunction of ...
- 413
2 votes
3 answers
90 views
Observing $L_x$ of a particle which is present in an eigenstate of $L_z,L^2$
I wonder what will be the probability of finding the particle in a particular $L_x,L^2$ state after we know its $L_z,L^2$. Definitely,the $L^2$ value will not change. Here is what I tried: First of ...
- 105
1 vote
0 answers
91 views
Intuition about the angular momentum term in GR gravity
Using the Schwarzchild solution and taking proper units to make $r_s=c=1$, we can obtain that the geodesic of a test object orbiting a non-rotating uncharged black hole can be seen as being attracted ...
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0 votes
1 answer
135 views
Problem involving two rotating discs [closed]
Two discs of radii $R$ and $2R$ are pressed against each other. Initially the disc with radius $R$ was rotating with angular velocity and other disc was stationary. Both discs are hinged at their ...
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