# All Questions

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### What is “a vector of $SO(n)$”?

I'm watching (or trying to watch) this lecture from NPTEL on classical field theory. I've understood everything in the series up till this point, including the first half of the lecture on elementary ...
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### How can I find the magnetic vector potential of an infinite cylindrical wire

I'm struggling with an exercise that asks me to find the magnetic vector potential $\vec{A}$ inside of an infinite cylindrical wire of radius $R$ given that the current per unit area ...
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### What is the cause of rolling friction? & why is it less than sliding friction?

Rolling friction is the resistance to motion experienced by a body when it rolls upon another. It is much less than sliding friction for same pair of bodies. When one body rolls upon another, there ...
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### Projecting gravity

From the title, this sounds like a question someone who is not familiar with gravity might ask. Before anyone answers or comments, I would like to say that I know gravity is a field and cannot be ...
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### What makes a nucleus unstable?

My question is simply that - what makes a nucleus unstable? What exactly causes a nucleus to start breaking apart in the first place? Is it the Coulomb force between the neighboring protons? I'm just ...
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### Finding the magnetic field of an infinite cylindrical wire

An infinite cylindrical wire of radius $R$carries a current per unit area $\vec{J}$ which varies with the distance from the axis as $J(s)=ks^2\hat{z}$ for $0<s<R$ and zero otherwise where k is a ...
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### Newton's law of resistance

Anyone can give me some clues on how this can be proved? What kind of drag force is used? A particle is projected vertically upward with an initial speed $v_0$ near the earth's surface. Show that ...
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### Cosmic Calendar [on hold]

So for an assignment I was given a event/ occurrence and was asked to find its cosmic date/ time. Here are a few examples of ones it asked for, I was wondering if there was a formula to find the date ...
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### Force per unit length between two long parallel wires, one of which is insulated

Suppose we have two very long parallel wires of radius $a$ and distance between their axes $d$ ($d>>a$). The first wire if is carrying charge of linear charge density $\alpha$ and is insulated ...
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### What exactly is black hole complementarity and why is it necessary for solving black hole information paradox?

What exactly is black hole complementarity and why is it necessary for solving black hole information paradox? The first question is about the story of vacuum fluctuation causing Hawking radiations. ...
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### Determination of Ricci tensor and Scalar curvature from vielbeins [migrated]

Consider the following metric: $ds^2=h(r)\bigg(dr^2+r^2\big(d\theta^2+\sin^2\theta ~d\phi^2+(d\psi+\cos\theta ~d\phi)^2\big)\bigg)$ We can try to compute the Ricci scalar of this metric by using ...
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### What role did the Higgs boson play in the Big Bang?

Scientists say that inflation stopped when a very peculiar energy was mobilized, did Higgs boson play any role in this? What is it's relation to the Big Bang? Some physicists, such as Michio Kaku, ...
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### Validity of the static limit of a dielectric function

In general, the dielectric function $\epsilon(q,\omega)$ reflects the spatial and temporal response of a condensed matter system to an applied potential. If we put an electron into an electron sea, ...
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### Can the energy of the universe ever be infinite in qunatum physics?

Suppose that the universe runs under some variants of QFT, with universal wavefunction and Hamiltonian. Then would infinite energy of the universe ever be possible? According to what I am thinking, ...
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### Maxwell's Inspiration to think about fields

I was looking at a Wikipedia article which had the following statement Atomists, notably James Clerk Maxwell and Ludwig Boltzmann, applied [...]. In modern literature Maxwell is often thought ...
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I am wondering if anyone can provide further info as to the preliminary principle involved in the filter shown below, any internet links would be appreciated. Is taken from a magazine related to ...
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### Why does time slow down when traveling at high speeds

One of the effects of traveling at high speeds is slowing down of clocks. I can understand gravity time dilation effect but not how would velocity affect clock speeds. How correct it is, if I say ...
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### How fast time goes in zero gravity [duplicate]

I understand that the effect of gravity is warping of space because of which object travels more through space dimension and less through time dimension, this is the reason for time slowing down in ...
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### Particle moving in response to central force

So I have this question: There is a particle moving in response to a central force per unit mass of $$F(r) = {\alpha\over r^2} + {\beta\over r^3}$$ where $\alpha$ and $\beta$ are constants. ...
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### Maximum cargo that can be supported by a hot air balloon

Imagine a balloon with a volume of 3471 m^3. The density of the hot air inside the balloon is .95kgm^-3 while the density of the air is 1.2kgm^-3. What is the maximum mass of the cargo that the ...
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### Does electron have angular momentum in orbital s?

I've read on science forum that electron in orbital s has no angular momentum and would fall into nucleus, so hydrogen atom would not be possible. Electron has mass and speed afterall right? So how is ...
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### Home experiment with airfoils and Reynold's number

I want to do an experiment about lowering the Reynolds number of an airfoil moving through air. I want to figure out how to lower the turbulence around an airfoil. So my two hypotheses to lower the ...
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### Why does U-235 split into barium and krypton in nuclear reactors?

For my chemistry project I have found the typical fission reaction which occurs in nuclear power plants is when nuclear fuel rods are bombarded with neutrons, splitting U-235 into isotopes barium and ...
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### Create air stream from heat

We know that heating the air inside a bounded box raises its pressure. And if there is a hole in the box, then air flows out until the pressure inside and outside balances. So in this case we would ...
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### Physics for Scientists and Engineers by Serway Beichner solution manual [on hold]

I have found this amazing book with all possible examples that I could imagine. It is very well written and structured. I have tried to solve some problems from the Problems Sections but I can't solve ...
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### Eigenstates of Spin

Why are the eigenstates of spin vectors and not functions? Is this because the spin, $s$, and magnetic quantum number, $m$, take discrete values? My textbook in an earlier section used $Y_\ell ^m$ as ...
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### How to determine speed/energy of something dropped from a given height?

Say I dropped a ball from some height, which is measurable, is it possible to determine the speed of the ball when it hits the ground and thus the force exerted on the ball my the ground (or vice ...
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### Will light leak into a side glow optical fiber?

I am looking into some possible applications of side glow optical fibers (plastic). Will side glow fibers "drive" adjacent fibers? That effect is undesired.
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### What forces are at work in a loose ball bearing bicycle hub?

I've landed in a physics debate amongst bike mechanics. In a typical bicycle hub you have a simple bearing; the cups are set in the hub, the race (cone) threads onto the axel and there are just loose ...
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### Proper way to write the units to indicate that they include an offset?

Past a certain point of complexity, I get rather confused with physical units, so I am asking a physicist for help. I have a code that represents temperature, with a resolution of [0.5 °C], whose ...
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### Calculating distance between two objects viewed from an angle [on hold]

I'm trying to determine the location of this vehicles rear bumper and the front edge of the white road marker. I can't tell if the vehicle is before, at the edge, or just ahead of the marker. The ...
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### The spin and weight of a primary field in CFT

A primary field in Conformal Field Theory transforms as $$\phi (z,\bar{z}) =\left(\frac{dz}{dz'} \right)^h \left(\frac{d\bar{z}}{d\bar{z}'} \right)^\bar{h}\phi (z',\bar{z}')$$ under a conformal ...
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### If infinite amount of different strong particles were to be confined and jammed together, what would occur? [on hold]

Consider this scenario; If an infinite amount of neutrinos, electrons, positrons, and photons of enormous wavelengths were to be confined, concentrated or jammed together in a relatively large space ...