# All Questions

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### Conductivity Matrix (Symmetry Information)

I'm trying to understand the symmetry content of the conductivity matrix: one information is, presence of time-reversal symmetry causes the off-diagonal terms to vanish. When this is broken (e.g. in ...
20 views

### Questions about the formula used to determine inductive reactance and $Z_t$

I am currently on the inductors unit in my Navy schooling and I have two questions about these formulas that I learned about. As I'm aware, the ability of an inductor to concentrate a magnetic field ...
40 views

### Confused about gravitational potential energy [duplicate]

So learning the concept of gravitational potential energy, my professor says that when lifting an object without any acceleration, the force we exert on the object to lift it is the same as the force ...
14 views

### Direction of induced EMF(and current) and Lorentz force direction?

Is the right hand rule for the Lorentz force (given the current and magnetic field directions)and the direction of induced EMF the same?
56 views

### Is superposition principle equally valid for both scalar and vector quantities?

I was wondering if superposition is even applicable to scalar quantities because scalars should simply add up to give final result as there is no sense of direction. Do we have any example of a vector ...
39 views

### How to prove that the net magnetic force in an arbitrary current loop is zero [on hold]

I believe that using Stokes' theorem makes this a laughing matter, because $$\mathbf{F}=\oint_C i d\mathbf{r} \times \mathbf{B}$$ Since the magnetic field is constant the $\nabla$ operator would ...
28 views

### How to calculate how much air is leaking out of an object?

I have a pressurated pvc pipe. I am wondering how long it would take for it to leak out on a small tube. I really just want to know how to do the equation, so I could figure it out depending on the ...
45 views

### Super Strong Magnets

I've seen the size of electric motors get smaller over the past 10-15 years...especially those used in small remote control vehicles like helicopters. I heard that the magnets being used in the ...
15 views

### Trying to calculate the length of a tube to heat Ar gas

If one were trying to heat Argon gas from ambient (~20C) through a mild steel tube of some diameter 'd' how long would it need to be? Additional unknown includes flow rate of Ar gas so some general ...
159 views

### Why is $\pi$ used when calculating the value of $g$ in pendulum motion?

I am trying to intuitively understand why $\pi$ is used when calculating the value of $g$ using the harmonic motion of a pendulum: $$g ~=~\frac{4\pi^2L}{T^2}.$$ Does it have something to do with the ...
18 views

### Finding net force [on hold]

Buoyancy and high altitude ballooning. Buoyant forces are supplied by every fluid (liquid or gas), it’s the mechanism that sends high altitude balloons all the way up to the stratosphere. For gases, ...
65 views

### Interaction pictures of Quantum Mechanics

I want to understand the Schrödinger, Heisenberg and interaction picture and have a few questions about them: So in general you have a time-dependent Hamiltonian $H$, as for example the potential may ...
10 views

### Addition of forces in dielectric material

In this paper (page 2 of document) it is said that: Because this calculated force was comparable to the gravitational force, they assumed that the same would be true for the forces on a ...
54 views

### Why do vapour cones form around jet fighters?

Apparently this phenomenon has nothing to do with jets breaking the sound barrier and has something to do with the Prandtl-Glauert singularity as described on Wikipedia. But, the Wikipedia article ...
33 views

### Projectile motion, solved with perturbation theory [on hold]

A ball is dropped from rest, the initial height is $h_1$. There is air resistance given by $-mkv$. In the downward motion, the equation of motion can by written as $$\dot v = -g-kv$$ with the y ...
25 views

### Discrete Symmetries: Breaking and Preserving

This is not a question, let's list down all the effects resulting from breaking or preserving of various discrete symmetries, on various observables, be it in condensed matter or in high energy. ...
21 views

### Atom in a box and collapse of the wave-function

Suppose I have an atom trapped in an optically transparent box. I'm assuming the atom is bouncing off of the walls and not bonding, i.e. the center of mass of the atom experiences a square well. Now ...
42 views

### Coupling of matter field with gauge boson and Goldstone boson:

What's the fundamental difference between the way a gauge boson gets coupled to a matter field, preferably a Fermionic field and the way a Goldstone boson gets coupled to the matter field ? In ...
19 views

### Finding most/least tension between 5 cars attached to a train [on hold]

I am currently doing Grade 11 physics and I have been troubled by this one question for homework for quite a while. Hopefully most of you will be able to help me out. Question: A 40,000kg train ...
23 views

### Calculate the density of this liquid and determine general formula for finding density of a liquid [on hold]

a) A 3.8 kg aluminum ball is found to have an apparent mass of 1.9 kg when completely submerged in a particular liquid. Calculate the density of the liquid. b) Determine a general formula for ...
254 views

### Having trouble understanding some stuff about delta functions [on hold]

I was going through one of the examples in Griffith's Quantum book and there was a few things in Example 3.3 that I didn't understand that I was hoping to get some clarification on. For instance, we ...
41 views

### Physical reasoning and mathematical problems [on hold]

After reading The Mathematical Mechanic: Using Physical Reasoning to Solve Problems by Mark Levi, I was wondering if there there are other books (or papers) that use a similar approach to explore ...
36 views

### 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 ?
32 views

### Covariant Nonlinear Transformation in two inertial frames [on hold]

I read about Lorentz transformation in my old lecture materials: and I started to think what would the matrix/tensor (or other structure, no matrix presentation exist, since matrices are linear) be ...
54 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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### 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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### 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 [duplicate]

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 ortho-para ...
218 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 ...
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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 ...
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### Calculate the flux of a point charge with Gauss's law

I know from my class that to calculate the flux of a point charge with Gauss's law, I have to make a surface that intersects with all of the flux lines resulting from the charge, and then make this ...
26 views

### Finding the initial velocity of a vertical circular motion [on hold]

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 ...
34 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 ...
24 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 ...
23 views

### How to calculate topological charge? [on hold]

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 ...
33 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 ...
37 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 ...
17 views

### 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.
59 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 ...
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### 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 ...
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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 ...
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### 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 ...
48 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 ...
97 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 ...
79 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 ...
1k 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. ...
576 views

### Failure of the Steady State Theory

I was reading a journal of astronomy and came to the most famous opponent of Big Bang theory: The Steady State Theory: The 20th - century theory was proposed by Hoyle,Gold and Bondie. The ...
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This is related with Equation 8.58 in Kerson Huang's 2nd edition of Statistical Mechanics. The partition functions for the ideal gases are given as $Q_N (V,T) =\sum_{\{ n_p \}} g\{n_p \}e^{-\beta ... 0answers 13 views ### How do we compute the volumetric efficiency of an engine which is based on forced induction? The volumetric efficiency of a naturally aspirated engine is computed by: $$n= \frac{V_1}{V_2}$$ With n: volumetric efficiency$V_1$: actual volume of air drawn$V_2\$: volume swept by piston ...

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