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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Spinning top moving in curved spacetime

If I have a spinning top in empty space, it would take work to change the orientation of the angular momentum vector of the top. Suppose I throw a spinning top in flat space such that the direction of ...
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The Fields of a Moving Point Charge and special relativity

David J. Griffiths Introduction to Electrodynamics page 456 shows the following figure: ... then page 461: ... and page 462: The following thought experiment has three electrons, negative charges, ...
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Why surface and bulk states of topological insulators (TI) have different topological invariants and how it leads to conductive states?

I am trying to understand how TIs work. Right now, the main thing I understand is that the surface states and bulk states have different topological invariants. This leads to spin orbit coupling being ...
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Angular Velocity of 3D object rotating in space

For a sphere rotating about z axis, its angular velocity is rate of change of angle of a radius vector in xy plane with x axis or y axis. I understand this clearly. But consider a 3d body which is not ...
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Can a translational torque cause a change in rotational angular momentum? gyroscope example

Please confirm if my understanding is correct: The example of a gyroscope suspended from a pivot is a case in which translational torque causes a change in the direction of rotational angular momentum:...
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How come the magnetic field disappears when a neutron star becomes a black hole, while the rotation remains?

The only question I found is this one, but this considers as non-rotating neutron star collapsing: Our final and most comprehensive test is represented by the collapse to a BH of a magnetized ...
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Does moving the idler in a wheel and disk CVT conserve energy or momentum? [closed]

Consider the wheel and disk CVTs (continuous variable transmissions) below. Configuration A comprises a CVT disk coupled to the "system under control" 's', whereby a control wheel 'cw' ...
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Does the direction of the torque acting on a car tire change depending on which direction the tire is rotating?

As I understand, the reason why unbolted car tires will fly off perpendicular to the direction of a moving car is because of the torque generated by the axel. This is unintuitive to me because there ...
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Photon wave function spontaneous emission

Consider some atom that decays from an $L = 1$ state to an $L = 0$ state, thereby emitting a photon. What would the photon's spatial wave function look like? I myself have considered two options: It ...
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Is intrinsic spin a quantum or/and a relativistic phenomenon?

Ok, this is my reasoning. I am probably making some wrong assumptions here, pls tell me where I am going wrong. Spin as a quantum phenomenon: Quantum phenomena disappear as the Planck constant goes to ...
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Energy loss on increasing moment of inertia

A body connected to a inextensible, massless string which is being spun around by a man in a circular path. The rope is then slowly released by the man from his fingers and stopped at a certain radius....
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If I define the operator L as: $$\vec{L}=\sum{\vec{l_i}}$$ where $\vec{l_i}$ is the operator of angular momentum of a single electron. How can I justify formally that $$\left[l_i ^2 , L^2\right]=0$$ ...