3
votes
1answer
3k views

Air Turbulence and DIY laminar flow hoods

So for years on the mycology, plant tissue culture, and DIY laboratory websites there has been this ongoing debate on how to achieve laminar flow in a home built laminar flow hood. Flow hood link! ...
1
vote
0answers
34 views

Phase functions non-existent in original (J. Strutt) Lord Rayleigh's work?

This is related to my previous Phys.SE question on the derivation of the phase function - upon sifting and scanning through 600 pages of John Strutt's collected work, there is absolutely no mention of ...
7
votes
3answers
372 views

How do I intuit viscosity in a rotating fluid?

Suppose I have two plates with a viscous fluid in between. I slide them in the same direction (a direction in their own plane), one at $5 \,\text{m/s}$ and the other at $6 \,\text{m/s}$. Due to the ...
10
votes
3answers
670 views

Where's the energy in a boosted capacitor?

Suppose I look at a parallel plate capacitor in its rest frame and calculate the electrostatic energy, $E$. Next, I look at the same capacitor in a primed frame boosted in the direction perpendicular ...
0
votes
1answer
175 views

Vertical velocity to reach a certain point given a flat horizontal velocity? [closed]

Suppose I have two points such as $a(4,6,9)$ and $b(32,5,12)$. If I have a flat velocity pointing $a$ to $b (b - a)$ which has an arbitrarily defined magnitude. Given gravity $g$,how can I calculate ...
1
vote
2answers
1k views

Time-reversal symmery and topological insulators

I have a very naive question about the notion of time-reversal symmetry applied to topological insulators that are studied in experiments. If I understand correctly, the exsistance of time-reversal ...
2
votes
2answers
1k views

Heat transfer between two surfaces

Suppose I have surface A in contact with surface B, if I apply Fourier's law of heat transfer, which $K$ should I use, $K_a$ or $K_b$? Essentially asking whether the same block of material heats ...
2
votes
3answers
467 views

If you could reverse gravity, what velocity would you achieve on leaving Earth?

If you could reverse gravity, to make it repulsive instead of attractive, what velocity would you achieve on leaving Earth? A simple question really, but I have completely forgot how to calculate ...
5
votes
2answers
777 views

How did Lord Rayleigh derive/determine the phase function for his scattering model?

I've been researching the question for quite some time, as I understand it the phase function is actually an approximation due to the particle-wave duality inherent in participating media such as the ...
2
votes
1answer
211 views

What if $F\neq \frac{dp}{dt}$?

I was thinking of this idea that maybe there are esoteric cases where the force is not given in classical mechanics as $F=dp/dt$ but as some function of $F=F(p,q,\dot{p},\dot{q})$ E.g, something ...
2
votes
2answers
439 views

What are the “loopholes” in past Bell's theorem experiments?

I am intrigued by the following Phys.org article: Researchers began using photons in 1980s to test Bell's theory and determine if Einstein's reasoning is right or wrong. Since then, researchers ...
2
votes
1answer
178 views

Which theory predicts that dubbed tires have more friction?

The physical reasoning I suppose could be that more contact areas mean more and higher friction. But is there an actual formula or a more mathematical explanation? Application for bicycling was my ...
0
votes
1answer
184 views

Lagrange L4 L5 points and perifocal plane

I have 2 satellites at the L4 and L5 points and these are watching an object. Each satellite provides the angle to the object from its own position from a line parallel to the $\text{x-axis}$ of ...
5
votes
2answers
423 views

Dark Matter 'Stars'

I'm aware that the Milky Way has a dark matter 'halo' around it, presumably a spherically symmetric distribution. But I'm completely ignorant regarding the theories explaining dark matter... Is there ...
0
votes
1answer
2k views

Calculating (Glass) thermal conductivity

I read that glass has a thermal coefficient of 0.8-1 W/mK. Given that my window window thickness is around $5\ mm$, then I would calculate my heat loss per area being $160-200\ Wm^{-2}K^{-1}$. Yet ...
4
votes
1answer
580 views

Is spacetime an illusion?

In consistent histories, for gauge theories, can the projection operators used in the chains be not gauge invariant? In quantum gravity, for a projection operator to be gauge invariant means it has ...
0
votes
1answer
105 views

Indicators on how even the heat is distributed?

I'm wondering if there are any good indicators on how even the heat is distributed on an object (for simplicity, a flat object maybe)? What are the possibly reasonable ways to maximize the evenness if ...
5
votes
2answers
638 views

Chiral edge state as topological properity of bulk state

As far as I know, quantum hall effect and quantum spin hall effect has chiral edge state. Chiral edge state is usually closely related with delocalization, since back scattering is forbidden. However, ...
2
votes
5answers
695 views

Forces acting on a point mass in a spinning rigid body

I have learned that all spinning objects will continue spinning even if no force is acting on it, and the tendency to do so is called moment of inertia. But I wonder about the fact that a single point ...
2
votes
4answers
1k views

Running a stirling engine in reverse?

I just bought a small stirling engine which converts heat flow down a temperature gradient into circular motion of a little wheel. If I turn the wheel with my finger, will the engine generate a ...
0
votes
1answer
646 views

Electric Fields

The problem I am working on is, "In the figure below, determine the point (other than infinity) at which the electric field is zero. (Let $q_1 = -2.45\ \mu C$ and $q_2 = 6.5\ \mu C$) Here is a little ...
7
votes
3answers
302 views

Falling through the rotating Earth

Suppose you were standing on the rotating Earth (not necessarily Equator or the poles) and suddenly your body lost the ability to avoid effortlessly passing through solid rock. Because the earth's ...
1
vote
0answers
33 views

Nuclear structure [duplicate]

Possible Duplicate: Are the protons and neutrons in the nucleus arranged in any particular way? Isotopes have different numbers of neutrons. Essentially my question is: how does the ...
4
votes
2answers
228 views

How do you fit a dipole in an electron?

Experiments used to observe particle spin properties (such as Stern-Gerlach) rely on a varied magnetic field and a dipole-like reaction in the particle, deflecting it in one direction or another. In ...
8
votes
2answers
3k views

The difference between the Wannier function and atomic orbit in a tight binding model

In a tight binding model, we usually start from the atomic orbits and linearly combine them to get the wave function of the crystal energy band. My questions are: Since this kind of tight binding ...
0
votes
3answers
439 views

What was wrong with action a distance?

It is usually said that the idea of fields was introduced (electric and magnetic fields) in electricity and magnetism after Coulomb's law to cure the conceptual problems of action at a distance. ...
2
votes
2answers
2k views

When do I apply Significant figures in physics calculations?

I'm a little confused as to when to use significant figures for my physics class. For example, I'm asked to find the average speed of a race car that travels around a circular track with a radius of ...
3
votes
1answer
656 views

Electric Field due to a charged sphere

Suppose we have a spherical surface with a surface charge density varying as $cos(\theta)$. Apparently one can find the electric field both outside and inside such a spherical surface by superposing ...
1
vote
1answer
118 views

Gyroscope bombardment

Let's say I have a spinning steel ball that I have somehow managed to be completely free in all axes of movement. If I fire a BB at it with enough force on a north-south (to the ball) angle, what will ...
6
votes
0answers
254 views

Prequisites to learn Topological Field Theory? [closed]

Sorry for the somewhat qualitative question but what are the essential prerequisites for someone wanting to learn topological field theory from say the more physical side of things? The math side also ...
2
votes
2answers
701 views

Expression for distance of closest approach in Schwarzschild Geodesics

The Wikipedia article Two-body problem in General Relativity uses two length-scale variables, $a$ and $b$, to simplify the math. For some information about these, consider these statements from the ...
4
votes
4answers
10k views

For an isolated system, can the entropy decrease or increase?

In any sizable system, the number of equilibrium states are much, much greater then the number of non-equilibrium states. Since each accessible micro state is equally probably, it is overwhelmingly ...
1
vote
0answers
86 views

Motivation For Definitions [closed]

I noticed in my physics textbook that we define certain relationships to be true. I can see how this is considerably helpful in deriving other relationships from these definitions; for instance, take ...
1
vote
2answers
459 views

What is the Riemann curvature tensor contracted with the metric tensor?

Can the Ricci curvature tensor be obtained by a 'double contraction' of the Riemann curvature tensor? For example $R_{\mu\nu}=g^{\sigma\rho}R_{\sigma\mu\rho\nu}$.
1
vote
1answer
108 views

Thermodynamics of a bar, specific heat

I have a problem and I don't understand how the book solves it. It says I have a bar such that $$F=aT^2(L-L_0)$$ where $F$ is the force or tension of the bar, $T$ is the temperature, and $L$ the ...
2
votes
0answers
58 views

Improvements on a makeshift dessicator

I am a first year undergrad working in a lab, and I have these Plexiglass containers that I tried to convert to dessicators, since the commercial bell jars are really expensive. I used these weather ...
2
votes
1answer
215 views

What are the statuses of Silicene and Graphene for real world circuit production?

A lot of hype is out there about both of them (especially the latter) and I was wondering if there is more concrete information about them other than the news IBM posted on a circuit 2 years ago and ...
2
votes
0answers
138 views

Supersymmetric Sigma Model

I was working through the Mirror Symmetry book by Clay Math Institute. It deals with supersymmetric sigma model in 10.4 section. It doesn't derive how the action is invariant under the variation. I am ...
0
votes
1answer
126 views

The equilibrium temperature distribution of a pan in vacuum

If a rectangular pan has a constant and uniform temperature $T$ first, then put it in a vacuum. Considering the effect of thermal radiation, the temperature distribution of the rectangular blackbody ...
1
vote
2answers
676 views

Monkey and tree - projectile motion

The famous scenario: A hunter is trying to shoot a Monkey hanging from a tree. However, this question doesn't mention the monkey jumping down from the tree or trying to escape. (The hunter uses a ...
2
votes
0answers
87 views

Where to find probability density plots for all elements?

Does anyone know where I can find something similar to this, but for all elements? I would love to find something with the same image quality. Also, is there any software that can produce images ...
0
votes
1answer
64 views

Hypotheses a hindrance in physics?

In a recent episode of the Big Picture Science podcast, there was an interview with Stuart Firestein (chair of the Columbia University Biology Department) in which he discussed his book Ignorance: How ...
0
votes
1answer
2k views

How do I find the magnitude and angle of the velocity?

I'm confused about the following problem. A ball is shot from the ground into the air. At a height of $9.1\text{ m}$, its velocity is $v = (7.6\hat{\imath}+ 6.1\hat{\jmath})\text{m/s}$, with ...
2
votes
1answer
414 views

Does special relativity unify the two phenomena at the base of Faraday's flux law (was Feynman wrong in this case)?

Consider Faraday's flux law for the EMF generated in a conductor loop: $$ \varepsilon = - \frac{d \phi}{dt},$$ where $\varepsilon$ is the EMF, and $\phi$ is the magnetic flux through the loop. ...
5
votes
1answer
332 views

Is there a maximum amount of photons that can exist in a certain amount of space?

If you have a set amount of space, lets say 10 cubic centimeters, and you would be able to trap photons in there. If you would then add more and more photons to that space, could you then go on ...
3
votes
3answers
164 views

Correct expression for D'Alembert operator in $c=1$ units

In QFT texts with $c=1$ units (most of them), D'Alembert operator is written as: $$\Box ={\partial^2 \over \partial t^2} - \nabla^2$$ For pedagogical purposes, however, some texts don't set $c=1$, ...
1
vote
2answers
69 views

Why is there no aberation of a static electric field, but there is aberation for EM radiation?

So consider the case where there is a particle and a moving telescope: If the particle is located at position 1, and the telescope is moving horizontally as shown, the EM radiation appears to be ...
2
votes
2answers
342 views

Charged quantum particle in a magnetic field - choosing a different gauge leads to different wavefunctions

Consider a charged quantum particle confined to the $xy$ plane, subject to a magnetic field $\mathbf{B}=B\hat{z}$. The Hamiltonian is: $$ H = \frac{1}{2m} \left( \mathbf{p} - \frac{e ...
3
votes
2answers
3k views

Harvesting electricity in the air from power lines:

Recently I came across this quote on the internet, about a person who apparently set up devices to extract electricity from the "air", on his own property: I read an article a couple of years ago ...
0
votes
1answer
1k views

Infinite square well in momentum space

As we know the eigenfunctions for a particle of mass m in an infinite square well defined by $V(x) = 0$ if $0 \leq x \leq a$ and $V(x) = \infty$ otherwise are: $\psi_n (x) = \sqrt{(2/a)} sin(n \pi ...

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