# All Questions

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### Concerning the transtition between matter dominated universe and radiation dominated universe

What caused the transition, and how to we know that this did not warp our calculations for the age of the early universe ?
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### Covariant Nonlinear Transformation in two inertial frames

I read about Lorentz transformation here: and I started to think what would the matrix be for any nonlinear transformation. Any existing examples? Wigner transform came to my mind. Is the matrix ...
1answer
20 views

### What will happen if a hairdryer is turned on in an air tight box?

I wanted to know what would happen if a hairdryer is turned on in an airtight box
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6 views

### Why does it appear that a Carnot Engine is allowed to reject less heat when $T_H$ is increased?

I'm struggling to understand a consequence of the definition of the thermodynamic temperature scale: $$\left( \frac{Q_H}{Q_L} \right)_{\mathrm{rev}}=\frac{T_H}{T_L}$$ This equation is valid for a ...
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13 views

### Are complex planes (Gaussian plane) examples for a Hilbert Space?

My assumption: Yes, even though from physical application point of view it looks like different. (A complex plane is used in complex AC analysis, while Hilbert Space refers usually to QM.)
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### Is time relative to the speed you are traveling

Is time relative to the speed you are traveling.. What happens when you reach the speed of light?
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### Behavior of Parahydrogen in a Magnetic Field

At low enough temperature, at equillbrium, the dihydrogen molecule is predominately parahydrogen, with the spins of the two protons opposite. Does an external magnetic field alter the equillbrium? ...
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83 views

### Teach me Wick's theorem the honest way

Generally speaking the average guy marginally acquainted with quantum field theory or advanced combinatorics describes Wick's theorem as some sort of correspondence between higher order differential ...
0answers
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### SUSY QM - working out energy spectrum and wavefunctions from a given superpotential

I'm currently self-studying F. Cooper and al.'s Supersymmetry in Quantum Mechanics, and I need help working out a particular case on shape-invariance. From a given superpotential of the form ...
2answers
16 views

### Calculate the flux of a point charge with Guass law

I know from my class that to calculate the flux of a point charge with guass law, I have to make a surface that intersects with all of the flux lines resulting from the charge, and then make this ...
2answers
17 views

### Finding the initial velocity of a vertical circular motion

A particle P is suspended from a fixed point O by a light inextensible string of length a. When hanging at rest under gravity at A it is given a horizontal velocity u. The particle moves freely ...
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19 views

### How to model a very simple spinning wheel

First off, I'm not a physics person, just a lowly software engineer with below average math skills. What I've written is a simple animation of a spinning wheel using C++/GTK/Cairo. It allows the user ...
1answer
19 views

### Ampère's law and superconductors

I have been reading about superconductors and emerge me a inquietude about the explanation of existence of currents inside the superconductor while their magnetic field (inside too) is zero. Based in ...
0answers
13 views

### How to calculate topological charge?

For a complex vector field in two dimensions with one or more phase singularity - a point where the field amplitude is zero and the phase is undefined - how do you explicitly calculate the total ...
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26 views

### Help me understand resonance

I don't fully understand how resonant chambers work. My confusion stems from the fact that they are passive elements or "filters", yet somehow are able to "amplify" the sound. Questions: How can I ...
1answer
31 views

### Tangential velocity of a parabola

For an experiment on the parabola motus we decided to calculate the velocity of the object thrown in three phases: When the object leaves the spring that throws it (we solved it using conservation ...
0answers
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### Is there a difference between spring fatigue and plastic deformation in springs?

Is there a difference between spring fatigue and plastic deformation in springs? Plastic deformation means permanent deformation in springs caused due to stretching in springs.
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34 views

### What is discrete phase space?

I've been reading a little about the usual, continuous Wigner functions and phase space quasi-distributions in general, and I believe I understand the idea behind them. The Wigner function arises when ...
0answers
18 views

### Recommend books on mechanics, motion and it's laws [duplicate]

I want a book that discuss all these things practically. I don't require it for any exam. Just for applying it confidently anywhere (want to Analyse fluids,thermo etc.) Want a book that explain how to ...
1answer
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### Finding voltage between two points in space

If electric field vector is defines as : $\vec{E} = \frac{V_0x^2}{a^3} \vec{i_x} + \frac{V_0y}{a^2} \vec{i_y}$ where $V_0$ and $a$ are known constants, $\vec{i_x}$ and $\vec{i_y}$ unit vectors of ...
1answer
22 views

### Separating the potential energy of a system of particles.

Assuming all forces derive form a conservative source and that all forces observe the strong form of the third law, how do we arrive at the following equation? V=\sum _i V_i+\frac ...
0answers
40 views

### Does the Noether's theorem apply to local symmetries? [duplicate]

Does the Noether's theorem apply to local symmetries? If yes, what is the conserved current in presence of the Gauge field $A_\mu$? I mean the conserved current is give by ...
1answer
73 views

### Intuitive meaning of a special case of the Bernoulli equation

In the Bernoulli equation, if $h$ equals zero, it reduces to $$P_1+\frac12\rho v_1^2 = P_2+\frac12\rho v_2^2$$ The equation does not have an intuitive meaning other than the fact that it is a bare ...
3answers
55 views

### Self-energy of electron from classical reasoning

If it takes energy to group charge together(self energy) how can it be possible for every single electrons, etc, to have exactly same amount of charge? (think of if we hold some sand in our hand, then ...
2answers
366 views

### How does Hendo hoverboards achieve the self-propelling motion? What is the MFA?

From what I understand of the idea behind Hendo hoverboards, they use four disc shaped hover-engines to generate a self-propelling motion. I also understand that it uses Lenz's law and eddy currents. ...
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15 views

### Spaceship orbital period [on hold]

So suppose a spaceship A is in a circular orbit around a Schwarzschild black hole of mass M in schwarzschild coordinates. And another spaceship B is hovering around with fixed $\theta$ and $\phi$ ...
3answers
439 views

### Failure of the Steady State Theory?

I was reading a journal of astronomy and came to the other most famous opponent of Big Bang theory: The Steady State Theory: The 20th - century theory was proposed by Hoyle,Gold and Bondie. ...
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### what make the bottom portion of a wheel in rolling motion move?

As I just learn about the rolling motion which is the combination of pure translation and pure rotation. The top portion of the rolling body has the speed of double speed at the center of the object ...
0answers
8 views

### What is the force of the wind resistance? [on hold]

A sled of mass 15.0 kg is pulled forward with a force of 35 N. Also a frictional force of 12.2 N acts on the sled. Finally a wind resistance acts on the sled. Over a period of 18.0 s the sled ...
2answers
77 views

### Gauge choice after Spontaneous Symmetry Breaking

After the spontaneous breakdown of local symmetry in presence of gauge fields (Higgs Mechanism), we can always choose a gauge where the Goldstone bosons are eaten up by the gauge field (also called ...
3answers
571 views

### Center of mass frame for massless particles

Given a scattering event where a photon and electron go in and a photon and electron come out, what is the center of mass frame? I'd say, since the photon has no mass, it's the rest frame of the ...
2answers
78 views

### Two carts connected by spring on frictionless track

I have the following homework problem: Consider two carts of equal mass m on a horizontal, frictionless track. The carts are connected by a single spring of force constant k, but are otherwise ...
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28 views

### Two Limits in Thermodynamics - Reducing Driving Force and Increasing Resistance

I just wanted to clarify what is probably a very obvious idea. Suppose I'm holding a a piston separating two containers at different pressures. If I release the piston, it will naturally move, ...
1answer
27 views

### Say, a liquid is made to flow in a tube. Why does the layers of the liquid in contact with walls of the pipe have zero velocity?

Say, a liquid like water is made to flow in a pipe. Why does the layer of water near the walls of the pipe have zero velocity? Does that mean that the layer of water near the pipe is stationary and ...
1answer
27 views

### What causes the recessed blade of some folding knives to emerge in a kinetic opening? [on hold]

KINETIC OPENING OF FOLDING KNIFE (FK) Several legal jurisdictions around the World, including Australia, have assented legislation/regulation which attribute the emergence of the recessed blade in the ...

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