0
votes
0answers
5 views

hamiltonian in a rotating frame

ˆ H0 = h(ωopt − Gx)a†a + hΩb†b··· this is the hamiltonian of optomechanical system how this can be solve after switching to a frame rotating at the incomming frequency ωL.
0
votes
0answers
2 views

Mass density of a cylinder increasing with the square of the radius

I’ve had to deal with a question like this on a test on friday and I just can’t get it out of my mind. I was supposed to calculate the moment of inertia of a cylinder with an inhomogenous yet ...
0
votes
0answers
13 views

High School Physics-Electromagnetism

An insulated smooth square frame ABCD of side a is able to rotate about one of its side taken as positive axis. The plane is initially located at x-z plane. A magnetic field present in the region ...
0
votes
0answers
7 views

magnetization curve for motors

I have query that if you observe magnetization graphs they are plotted between flux and armature induce voltage keeping speed constant but how does it happen ? Did every time to keep speed constant ...
-2
votes
2answers
23 views

Origin of time or origin of space-time?

This might be a mere theoretical concept and I might even get down voted for asking this. I read in several sources that winding back general relativity equations leads to $t=0$, origin of time. ...
-1
votes
0answers
28 views

Why move from Special Relativity to General Relativity? [on hold]

The concept of relativity is simple. Why take Maxwell's equations to a new Special Relativity level with the unproven assumption that photons have no mass? All other physical data (momentum, affected ...
0
votes
0answers
21 views

Does “Schrodinger's cat” need entity knowledge to work?

I've never studied physics, but am interested in whether this paradox, from an interpretation of quantum mechanics, can still be stated if we don't know anything about unobservable entities. My ...
1
vote
1answer
24 views

Pressure loss in an infinite pipe

I feel lost in this problem. I know pressure loss occurs in a pipe flow due to friction. Say given a constant diameter pipe, if we keep lengthening the pipe horizontally, and static pressure will ...
0
votes
0answers
4 views

Speed of sound at phase transition — does percolation theory describe it?

I was discussing with a friend whether we expected liquid water or ice to have a higher speed of sound, near freezing; we figured it would be water since it was more dense. It turned out to be ice (by ...
0
votes
1answer
24 views

basic question about work exercise

I am learning independently from Tobochnik's statistical physics text. He asks a warm up question about work: A person pushes a block up a frictionless ramp. Is the work positive, negative, ...
4
votes
1answer
28 views

How can IR cameras see things colder than the camera?

I’ve read that only cold-blooded animals develop IR vision to spot warm prey because a mammal would blind himself with his own heat and not be able to see anything. But I’ve seen a FLIR camera, ...
0
votes
0answers
14 views

Spectral covers and a specific exact short sequence

I have a question about the spectral cover construction of Friedman, Morgan, and Witten (typically used to map a description in heterotic string theory into F-theory). I realise this is a highly ...
0
votes
2answers
20 views

Initial Velocity Question

What is the initial velocity vertically when a person jumps 0.5 metres into the air, neglecting horizontal movement. Is it just 0 m/s? And the final velocity would be -9.8m/s^2 * the time it took took ...
1
vote
0answers
13 views

How much energy is released by decompressing water?

How much energy would be released if 2L of (relatively pure) water compressed to 1L at room temperature was suddenly decompressed to atmospheric pressure? Even a first-order approximation would be ...
1
vote
0answers
10 views

Frequency range possible from a mechanical music box

Here is a small mechanical music box. The tines of a metal comb are tuned to emit a particular frequency when plucked. The material and structural characteristics of the comb, plucking cylinder, ...
1
vote
1answer
26 views

If we harvest energy generated by Coriolis Effect of the earth, will the earth slow down?

Coriolis Effect causes strong winds in the upper atmosphere, and it's purely due to differences in the linear velocity of Earth's rotation across latitudes. Now the Earth is spinning with the energy ...
0
votes
0answers
19 views

When we say particle in a box has quantized energy, is that kinetic or total energy?

In quantum mechanics, it is usually said that energy of the bound (constrained) systems such as particle in a box (infinite potential well) is quantized. It confuses me exactly what type of energy is ...
0
votes
0answers
12 views

Motion in a Plane Velocity

If I were to throw a rock of a cliff at 12 m/s as a horizontal velocity, what will the final velocity of the rock become when it hits the ground? I am tempted to say 12 m/s because the horizontal ...
0
votes
2answers
28 views

Action at a Distance

Since photons move at $c$, do they experience time or distance? If they don't, doesn't this explain action at a distance? From the point of view of the photons, there is no time, so the action at a ...
1
vote
2answers
25 views

Could a strongly enough charged black hole allow for a strongly charged particle to escape the event horizon?

If there is a strongly charged black hole, and a particle with a strong charge of the same sign goes inside of the black hole's event horizon while moving quickly, is there a reason why it would not ...
0
votes
0answers
9 views

Electric octupole moment in cartesian coordinates

I'm trying to calculate the symmetric traceless tensor for the octupole moment in cartesian coordinates... I have to deal with the electrostatic potential of the form: $\Phi^{(4)}(\textbf{r})=\int d^{...
-1
votes
1answer
25 views

What happens with QM particle at constant velocity?

In QM particles have wavefunctions that disperse quite fast. The FWHM for gaussian wavepacket increases in time as $\Delta x(t)= \Delta x_0\sqrt{1+(t/\tau)^2} $, $\tau=2m(\Delta x_0)^2/\hbar$ What ...
3
votes
0answers
29 views

Why do these experiments contradict the accepted theory about puddles?

A few months ago, I tried to tackle the problem of finding the shape, the height and other properties of a puddle (whenever a few mL of some liquid are dropped in a "uniform way" so that the puddle ...
0
votes
1answer
35 views

How feasible is it to power your home with a bicycle?

This article claims "60 Minutes On This Bicycle Can Power Your Home For 24 Hours!" How feasible is this claim? Sounds great - but the skeptic in me says "yeah, right." Hope this is an acceptable ...
0
votes
0answers
26 views

How does this dumbbell rotate?

I am reading the book Spacecraft Attitude Determination and Control by J.R. Wertz, and on page 488 it says: My question is: how does the axis of rotation, $\hat{\omega}$, rotate? How does ...
-1
votes
0answers
7 views

Motion in a Plane Question [on hold]

I don't understand how to do this problem: You are the pilot of a small plane and want to reach an airport, 600km due south, in 4.0h. A wind is blowing at 50km/h[S35oE]. With what heading and ...
0
votes
0answers
10 views

Interpretation of Evanescent Elastic Waves for Material Damage

In elastodynamic theory, when the slowness vector is imaginary, the resulting elastic waves are called evanescent. I have read that this corresponds to exponential decay. I have also read that complex ...
0
votes
1answer
20 views

Heating water in a pot from a constant heat source

What are the equations used to calculate the amount of energy transferred from a constant heat source "like a stove" to a pot which would then transferred energy to water contained in that pot. I don'...
2
votes
2answers
31 views

Why do magnetic coils consist of many thin wires?

Magnetic coils are usually made of thin wire turned into spring shape: Magnetic field which is generated by this solenoid is proportional to the number of turns N...
3
votes
1answer
29 views

Is it possible to quantify the work required to introduce order?

Is there a thermodynamic analysis that allows us to say "in order to introduce this much order into this subsystem, this much work must have been done on it by the rest of the system"? I assume that ...
3
votes
1answer
30 views

X-Ray diffraction - Braggs law

"Based on the Bragg equation, if crystal A has larger spacing in its diffraction pattern than crystal B, what conclusion can you draw about the spacing between layers of atoms in A compared with B?" ...
9
votes
3answers
797 views

Are black holes perfect spheres?

What I know about black holes (correct me if I'm wrong) is that they are the most compact objects in the universe that have been discovered. Due to all that gravity, wouldn't black holes be a perfect ...
3
votes
2answers
46 views

Does the charge of a black hole affect its space-time geometry?

Does a black-hole of a given mass and angular momentum have the same space-time geometry regardless of its charge? I'm pretty sure that an electric field can accelerate a charged particle but doesn't ...
3
votes
2answers
295 views

What's smaller: a neutrino, or a string from string theory [on hold]

I've recently read an article that stated "If an atom were as big as the solar system, a neutrino would be the size of a golf ball". I watch the science channel, and on (I believe) the show How the ...
0
votes
2answers
34 views

Question regarding elastic collisions and the conservation of momentum / energy

I've been working on this question for a few hours and I cannot quite convince myself that my answer is correct. I've read the relevant section in my textbook, but I guess the lightbulb just isn't ...
0
votes
0answers
21 views

How far would the atmosphere have to extend before we couldn't see the sun?

Ignoring dust, haze, clouds or ice crystals. Just 100% clean air.
1
vote
0answers
13 views

Chemical Potential of Interacting Particles

I'm interested in studying the diffusion of (classical) particles that have some interaction with each other. More specifically, let the potential energy of any two of particles separated by a ...
2
votes
2answers
64 views

Two particles system

Source: this video For a system with two particles (09:30), why is its wave function a product of each particle's wave function? E.g. $$\psi(x_1,x_2)=\psi_a(x_1)\psi_b(x_2)$$ For indistinguishable ...
0
votes
0answers
29 views

When should parameters be replaced while changing basis?

I have the following equality: $$a\lvert 00\rangle + b\lvert 11\rangle = a\lvert ++\rangle + b\lvert --\rangle$$ for any $a,b \in C$ that satisfy the normalization condition. For $a = \frac{1}{\...
2
votes
1answer
55 views

Express state as eigenkets

This is very basic but I just suddenly got confused. Any state can be expressed as complete set of eigenkets with discrete eigenvalues: $$|P\rangle = \sum^n c_n |p_n\rangle$$ I understand the above. ...
1
vote
1answer
68 views

Charge of electron in AC/DC circuit

If electrons in a DC circuit going through a metal wire carry only negative charge from negative to positive, then in a AC circuit through a wire does a electron carry both a negative charge and ...
1
vote
2answers
56 views

Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...
5
votes
0answers
38 views

Where does a fermionic coherent state live (which Hilbert space)?

There have been a couple of questions on fermionic coherent states, but I didn't find any that covered the following question: If I define a coherent fermionic state in the 2-level-system spanned by $...
0
votes
0answers
18 views

States after measurement

I am learing about quantum mechanics, and I am quite unclear about the the role of measurement and the density operator. Let $\mathcal H$ be a Hilbert space, $\psi(t) \in \mathcal H$, $O$ be a ...
-4
votes
1answer
34 views

Why can't rotating magnets in space or zero gravity be used to create infinite energy?

I would like to know if a system like the one below will possibly work. I understand that the laws of physics forbid the "creation" of energy but despite my efforts I haven't been able to figure out ...
-2
votes
0answers
31 views

What are ${\cal N}=4$ and ${\cal N}=2$ theories?

I often hear of ${\cal N}=4$ and ${\cal N}=2$ theories. For example, in the talk. What are ${\cal N}=4$ and ${\cal N}=2$ theories? Are there some ${\cal N}=k$ theory, $k \neq 4, 2$?
-2
votes
1answer
22 views

Force dependence on velocity : Drag

I just listened to the second lecture of Leonard Susskind on classical mechanics where he discussed that force can't be proportional to velocity, since it's unable to retro-dict (predict past). He ...
0
votes
1answer
32 views

Proper definition of the Wannier function

I am studying the construction of the Wannier functions for 1D system with periodic boundary conditions and my reasoning seems to be a little bit different from what I can find in textbooks. First ...
1
vote
0answers
24 views

Sectional curvature of 3-hyperbolic space [migrated]

For a pair of $(X,Y)$ of linearly independent vectors in $T_pM$, $p\in M$, the sectional curvature is defined as $$K_p(X,Y)= - \frac{\bigl\langle R(X,Y)X,Y\bigr\rangle}{|X|^2 |Y|^2 - \langle X,Y\...
1
vote
0answers
17 views

Spikes and valleys of ferrofluid

I can understand that the spikes are formed because of the elongation of the ferrofluid due to the difference in forces experienced by the two ends of the particle. But I can't understand why there is ...

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