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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1answer
42 views
interpreting aspects of rotational motion conceptually [closed]
Level - First Year Physics University
I don't understand the concept of angular momentum, conceptually. What is it? if I were to explain it how would I go about doing that? without having to explain ...
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0answers
54 views
Closed-form equation for orientation and angular velocity over time
If a rigid body, rotating freely in 3d, experiences no friction or other external forces and has an initially diagonal inertia matrix $\mathbf{I}_0$ (with $I_{11}>I_{22}>I_{33}>0$) and ...
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0answers
78 views
Conservation of Angular Momentum: atomic transitions vs exciton decay
I have a question about the role of photon angular momentum in two different sets of selection rules:
In atomic transitions within the dipole approximation, I've seen the selection rule as:
$\Delta ...
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2answers
122 views
Spin of a particle and spin quantum number [duplicate]
what actually does the spin quantum number of a particle describe about? What it means when we say photon has spin 1, Higgs boson has spin 0, etc..?? What actually does that numerical value explain? I ...
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0answers
122 views
How is multiplicity given by 2S+1?
Suppose there are two electrons in an atom with $s_1 = \frac{1}{2}$, $l_1 = 1$ and $s_2 = \frac{1}{2}$, $l_2 = 1$. Hence the total $S$ (of the atom) may be +1 or 0. And total $L$ is either $+2$, $+1$ ...
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1answer
50 views
Relationship between angular momentum of Earth and recession rate of the Moon
So the problem goes like this:
Two masses $m_1$ and $m_2$ orbit each other with semimajor axis $a$. The orbit is circular, and $m_1 \gg m_2$. The body $m_1$ has a rotational moment of intertia $I_1$ ...
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1answer
177 views
Having hard time with Angular Momentum and Parallel axis theorem
I'm having hard time with Angular Momentum and Parallel axis theorem.
Please explain these 2 formulas. Is one formula derived from the other?
$$J = J_{cm} + R_{cm} \times P_{cm}$$
$$I = I_{cm} + ...
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0answers
36 views
Calculate Rotational Intertia
If a can of soup, and a can of beans (tightly packed), are set in a race down a rough hill (has friction), the soup wins, because the inside of the can (soup) is not drawing energy from the system.
...
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0answers
47 views
Wigner $3j$ symbols
I am trying to determine the expansion that requires using $3j$ symbols; however, I am running into some conceptual snags. First, the expansion produces symbols that have m's that do not agree with ...
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2answers
192 views
How to write Schrodinger equation when a particle with some spin quantity and orbital angular momentum
Quantum mechanics: Suppose that there is a particle with orbital angular momentum $|L|$. But the particle also has spin quantity $|S|$. The question is, how do I reflect this into Schrodinger ...
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1answer
255 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 ...
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0answers
145 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 ...
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1answer
74 views
Vector cross product of $\mathbf{r}$ and $\ddot{\mathbf{r}}$ in polar coordinates
I'm struggling with the following question:
Question 6 A planet of mass $m$ moves under the gravitational attraction of a central star of mass $M$. The equation of motion of the planet is
...
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2answers
61 views
Is my physics correct or torque correct?
I would like to put this into a differential equation. This is what I have.
$$r \times F = I \ddot\theta + \mu \dot\theta + k \theta$$
What I need verified:
$\text{Torque} = I\ddot\theta + \mu ...
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1answer
575 views
Derivation of angular momentum commutator relations
I'm trying to understand the derivation of the angular momentum commutator relations. How is
$$[zp_y, zp_x] ~=~ 0?$$
How is
$$[yp_z, zp_x] ~=~ y[p_z, z]p_x?$$
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1answer
122 views
What is the meaning of change of angular momentum of a ballistic object during its flight?
In a 2D world, three stones, whose magnitude of initial velocities are 5000m/s, are thrown from the North pole towards the Equator with horizontal initial angles of 15o, 30o, 45o and 60o angles. Their ...
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1answer
87 views
Period of an Object in Periodic Motion
My attempt (if it matters):
The initial period is given by $T_X = \frac{2\pi X}{v}$ for some $v$.
The new period is given by $T_Y = \frac{2\pi Y}{v}$ for the same $v$.
$Y = \frac{X}{2}$, so ...
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1answer
182 views
Interaction of polarized beam to optical active substance
Kostyas question for angular momentum and half wave plates
Half wave plate and angular momentum
made me think a little bit. It took me some seconds to "swallow" the answer. :=)
Then I started to ...
0
votes
1answer
146 views
How is torque equal to moment of inertia times angular acceleration divided by g?
How is the following relation true
$$\tau = \large\frac{I}{g} \times \alpha$$
where $\tau$ is torque,
$I$ is moment of inertia,
$g= 9.8ms^{-2}$,
and $\alpha=$ angular acceleration.
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1answer
78 views
Calculating the moment inertia for a circle with a point mass on its perimeter
I want to calculate the tensor of the moment of inertia. Consider this situation:
The dot represents a points mass, in size equal to $\frac{5}{4}m$. $m$ is the mass of the homogenous circle. I'm ...
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1answer
85 views
A sphere rolling down a rough wedge which lying on a smooth surface
A sphere of mass $m$ and radius $r$ rolls down from rest on an inclined (making an angle $\phi$ with the horizontal ) and rough surface of a wedge of mass $M$ which stays on a smooth horizontal floor. ...
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1answer
67 views
Angular Momentum Addition Theorem
If I have, for example a particle with $s = 3/2$ and $\ell = 2$, what are the allowed values of $j$?
I'm slightly confused because I know that $j = \ell + s$, so surely there is only one allowed ...
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1answer
219 views
Angular Momentum of Diatomic Molecules
I have run into a problem trying to calculate angular momenta and I wonder if someone can set me straight.
I think I know that the lowest order rotational mode should have angular momentum of h, and ...
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2answers
556 views
Torque And Moment Of Inertia
I am reading the two concepts mentioned in the title. According to the definition of torque and moment of inertia, it would appear that if I pushed on a door, with the axis of rotation centered about ...
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1answer
338 views
Probability of getting a particular spin
I'm a beginner in quantum mechanics, and I'm a bit confused about states and the probability to measure certain values. I would like to understand at least the following simplified situation:
...
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3answers
3k views
Period of Precession
I'm trying to find the period of precession for a gyroscope. Now I was able to find the angular precession rate, which was 1.132 rad/s, but I have no idea how to convert this to a 'period', and google ...
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0answers
31 views
what happens to the angular velocity of star in star-black hole system?
What happens to the rotational and revolutionary angular velocities of star in star-black hole system as the star loses mass ?
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0answers
32 views
Confusion in connected pulleys problem
I'm having some troubles in understanding why my reasoning doesn't work in the following problem:
Problem Two pulleys of mass $m_1$,$m_2$ and radius $r_1,r_2$ are connected by a belt (like chain ...
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votes
0answers
54 views
Conservation of angular momentum tensor $L^{\mu\nu}$ in special relativity [duplicate]
I have edited this question because I don't think that the related post answers my question fully. It refers to Noether's theorem but I would like an explicit illustration in an easier fashion: The ...
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2answers
99 views
Internal/Rotational angular momentum
I have some difficulties to understand the relation between the internal and the rotational angular momentum of a rigid body which is also known as König's theorem, so what physical intuition lies ...
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0answers
46 views
What exactly is the spin of a particle? [duplicate]
Possible Duplicate:
What is spin as it relates to subatomic particles?
I'm having a hard time grasping the concept of spin, my textbook describes it very vaguely:
Stable matter contains ...
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votes
1answer
283 views
How do I find the eigenvalues for the angular momentum ladder operators?
I am trying to calculate the normalising constants for the angular momentum ladder operators but am stuck when I need to calculate expected values.
How can I find the expected values
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votes
0answers
67 views
Help course exercises vol.1 Cap Berkeley. 6 [closed]
1 2. Angular momentum of tetherball. The object of the game
tetherball (Fig. 6.24) is to hit the ball hard enough and fast
enough to wind its tether cord in one direction about the
vertical post to ...
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0answers
222 views
Moment of Inertia Tensor about non-principal axis
I'm part of the Western Martial Arts/Historical European Martial Arts community, and a debate that often comes up is parrying with the edge vs parrying with the flat of a blade. I want to do some ...
0
votes
0answers
102 views
Why angular momentum applies to emitted photons, and how it affects the emitting atom's quantized system
From what I've read, photons have spin of 1 (I guess possible by their relativistic mass), and when a photon is emitted from an atom, the production of this spin affects the balance of the atom's ...
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0answers
837 views
Moment of Inertia problem [closed]
I'm revising for my exam and there's this one problem where I can't get the correct answer, so I'd like to know how to solve it. The problem is:
Two boys, each with a mass of 30kg, are sitting ...
0
votes
0answers
69 views
How to control heavy ball in x and y direction? [closed]
I'm trying to build a device that holds a rather heavy ball and I want to be able to control it's "movement" in the X and Y directions (they are horizontal as well as orthogonal).
My current ...
0
votes
1answer
173 views
Angular momentum conservation in a central field through the Hamiltonian
In my teacher's notes there is a discussion of the Hamiltonian for a central force field with potential $V(r)$.
The Hamiltonian is formulated in spherical polar coordinates:
...
0
votes
0answers
192 views
Am I doing this conservation of angular momentum problem correctly? [closed]
I am doing some calculations for a practical project of mine. Basically I have a levitating sphere with gravity countered and close to 0 friction when the sphere rotates(due to airdrag). Inside the ...
-1
votes
1answer
557 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 ...
-1
votes
1answer
112 views
Can an electric motor force angular momentum not to be conserved in an isolated system?
An ice skater is in a spin, she pulls her arms in and she spins faster, she lets her arms extend outward and then she starts to slow down.
She will probably weigh on a weigh scale about the same ...
-1
votes
1answer
85 views
Implications of rotational invariance
The state
$$|\psi\rangle ={1\over \sqrt 2}(|+\rangle|-\rangle-|-\rangle|+\rangle)$$
of system made up of 2 spin-$1\over 2$ particles is invariant under the operator
$$\exp{i\theta S_y}.$$
What ...
-2
votes
0answers
46 views
Rotating pipe with bug [closed]
A thin mass less horizontal pipe rotates about a vertical axis with angular speed $ω$ as shown in the figure. A small bug, located at a distance $r$ from the axis, starts crawling inside the pipe at ...
