# All Questions

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### problem with spin connection term

While working out Kaluza Klein compactification, I am getting the unwanted spin connection term $\omega_{c}^{ac}$ .I have tried to show that this is zero.But I am not quite sure of it. What I tried ...
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### How can I understand how $\text{m}^2/\text{s}^2$ is related to $\text{J}/\text{kg}$?

$E=mc^2$ is the famous equation that states the equivalence of mass and energy, with a conversion factor in units of $\text{m}^2/\text{s}^2$. But in my naive mind, the conversion factor of mass and ...
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### Approach to model solvent in a lattice: e.g. H2O in NaCl

If a lattice contains a solvent, lets say NaCl and water of crystallisation, what is the condition for a solvent molecule to change it's location? From my current point of view I assume that such a ...
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### A question about finding average velocity and average acceleration

I have trouble understanding the following problem's answer: Which of the following relations are true for any arbitrary motion in space? (a) $v_{avg}=\frac{r(t_2)-r(t_1)}{t_2-t_1}$ ...
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### Find distance with zero net electric force [on hold]

I am new to the site (and physics!), sorry if this is too elementary or something. I have this problem that I can not solve - perhaps you could help?! Thank you!
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### If an asteroid were threatening the Earth, could I deviate it just by jumping on it?

An impact by a 10 kilometres asteroid on the Earth has historically caused an extinction-level event due to catastrophic damage to the biosphere. There is also the threat from comets coming ...
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### Group velocity and phase velocity of a wave packet [on hold]

A wave packet in a dispersive medium is represented by the following equation, $$y(x, t) = \cos(1.0x - 5.0t)\cos(0.2x - 0.4t)\cos(0.1x - 0.2t).$$ Find the group velocity and the phase velocity ...
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### What is the yield strength of a bar of different cross sections?

Will the yield strength of the combination will be same as that of the rod of uniform cross section?
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### I need help using Faraday's Electromotive Equation? [on hold]

I don't understand why the answer in my book is -17.93 mV for Practice Exercise 9.2. I tried solving it on my own but I'm certain that it should be 0 since the dot product is 0. Could someone show me ...
31 views

### Error calculation for experimental data

I have the list of experimental values: $$\{w_i \pm \Delta w_i\},$$ where $w_j$ is a mean value and $\Delta w_i$ is an error. I want to calculate the second list $\{a_i \pm \Delta a_i\}$ according to ...
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### Dielectric resonance spectroscopy of thin and thick film

How does the technique vary for dielectric resonance spectroscopy for thin film of ~ 3 micrometer and a relatively thick film of 100 micrometer?
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### Finding the contained charge in a box, given the $E$-field [on hold]

I'm not sure whether my approach is correct for this problem, it's been a while since I've touched E&M. I thought it best to check, as I'm not sure whether $0$ is the proper answer. I've got a ...
22 views

### Calculating relaxation time

When exploring the viscoelastic properties of glassy polymer like PMMA, there are usually two relaxation mechanism: alpha and beta. Usually beta relaxation time varies with temperature following ...
18 views

### How to compute Pressure, if acceleration is not given on the Force? [on hold]

I just need clarification on this if my theory is right. This to acquire the pressure applied on a foot of a person. Supposed that the measured mass or weight in the right foot is 50kgs when the ...
42 views

### Why is Buoyant Force $V\rho g$?

For a submerged object, buoyant force ($F_b$) is defined as: $$F_b = V_{\text{submerged}} \times \rho \text{ (density)} \times g \text{ (gravitational constant)}$$ Conceptually, the buoyant force ...
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### Stern-Gerlach experiment theory question [on hold]

I have an assignment problem which I've been having some difficulty with. i know the answer but I want to know how to arrive at it correctly, and want to know where I've gone wrong. Determine the ...
21 views

### Why don't neutral atoms distort the electric field?

Suppose I have a positively charged conductor with a cavity. There's a positive charge inside the cavity and the system has reached electrostatic equilibrium. Then there's negative charge surrounding ...
680 views

### What is the square root of the Dirac Delta Function?

What is the square root of the Dirac Delta Function? Is it defined for functional integrals? Can it be used to describe quantum wave functions? \begin{align} \int_{-\infty}^{\infty} ...
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### Do all elements spectrum lines fall within the visible light range?

I was wondering if whether we were extremely lucky to have found spectral (absorption) lines of astronomical objects because they fell within the visible light range or if there something intrinsic ...
118 views

### Determine if Theory is Unitary from Lagrangian

Question: Given a quantum theory specified with a Lagrangian and the degrees of freedom to be varied, what is the procedure to determine if the theory is unitary or not? Concrete example to aid ...
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### Simple gas in cylinder modeling

I want to do a simple (physically plausible but not physically accurate) simulation of a gas in a cylinder as it works on or is worked on by a piston. Wikipedia gives a good example of an adiabatic ...
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How it this possible? Even if the gif is fake, the Mythbusters did it and with a large sail it really moves forward. What is the explanation?
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### What does the first column in the “decay modes” table mean (in Particle Data Group documents)?

As a follow-up to this more general question, what are the values in the first column of each of the "decay tables" in a PDG document describing? What are those things in the first column? Are they ...
43 views

### With respect to the doppler effect, are pitch changes sudden or gradual?

Take this excerpt from Wikipedia regarding the Doppler effect: if the siren approached the observer directly, the pitch would remain constant until the vehicle hit him, and then immediately jump to a ...
81 views

### Why work $W$ and heat $Q$ are different concepts?

I understand heat as the flow of energy (through radiation, convection or conduction) from one body to another. When I think about conduction (for example) I visualize particles that jiggle a lot ...
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### D7 brane profile

I have a doubt about the differential equation leading to the profile of a d7 brane embedded in a 10 dimensional space. According to http://arxiv.org/abs/hep-th/0306018, equation (6), we have the ...