# All Questions

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### pressure on a sealed vessel

If a sealed vessel can withstand being submerged to 2 atm external pressure with 1 atm inside, is this the same as the vessel at 1 atm with high vacuum within the vessel? Sorry, I know this should be ...
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### What makes a matrix a tensor in special relativity?

Is any matrix a tensor in special relativity? My question is inspired by the definition of the electromagnetic field tensor in Carroll's Spacetime and Geometry book. In equation (1.69) he defines a ...
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### String-like theory

What is the general theory that describes the interactions between strings. I mean the basic object in the theory is (closed) string and they have interactions among them. The string theory, as I ...
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### How to determine the pressure of the moving water at the bottom of a vertical pipe [on hold]

Water is flowing upwards in a vertical pipe with an inside diameter of 0.06 m at a velocity of 0.0152 m/s. The length of the pipe is 0.5 m. What is the pressure at the bottom of the pipe? Density of ...
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### Phase space volume and correlation dimension

This may seem trivial but I will appreciate help in determining the functional form of the probability density function (pdf) for the following case. Will highly appreciate some guidelines on how to ...
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### Interpretation of $\vec{x}$ in QFT

I am still at an early stage of studying QFT (QFT in a nutshell by A. Zee), and maybe (and maybe not..) the answer to this question would emerge from the text book/s later, but, I'm still going to ask ...
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### How to calculate Gibbs free energy of diamond?

How the effect of crystal structure on Gibbs free energy is calculated? For example, how the Gibbs free energy of diamond is 2.9 kJ/mol, while that of graphite is 0?
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### How is taking the average of an integral over an interval justified?

I have been studying classical mechanics and often when going through a worked problem I see a step where there is an integral from 0 to 2$\pi$ of $\sin^{2} \theta \ d\theta$. Instead of using the ...
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### Specific volume of an air parcel [on hold]

So I have an unsaturated air parcel in the atmosphere that ascends adiabatically from the $1000$ mb level to the $700$ mb level with it's initial temperature being $10$ degrees Celsius. I have to ...
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### Units of acceleration & Newton's 2nd Law

I tried to use Newton's second law, $F=ma$, to calculate the acceleration of an object, what am I doing wrong ? \begin{align}\frac{F}{m}&=\frac{ma}{m} \\ a&=\frac{F}{m}=\frac{30\,\rm ...
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### If I squeeze something really hard, will it ever become two-dimensional?

A mosquito just wanted to bite me! Päng - and it stuck to my hand, hardly recognisable anymore. I said to my girlfriend: "Just reduced the dimension of the mosquito by one!" Therefore the question: ...
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### Density matrix formalism and group representation

The postulates of quantum theory can be given in the density matrix formalism. States correspond to positive trace class operators with trace 1 on a Hilbert space $\mathcal{H}$. Composition is defined ...
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### Does gravity affect magnetism, vice-versa, or do they “ignore” each other?

I am suddenly struck by the question of whether gravitation affects magnetism in some way. On the other hand, gravity is a weak force, but magnetism seems to be a strong force, so would magnetism ...
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### Complex Quantum Wave

Can we explain complex nature of quantum mechanics in the following way? Experimentally we do know that quantum particle behaves like a wave, but generally particle is well defined in space and can ...
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### how do I resolve this velocity into components? [on hold]

my problem is: And this is the diagram I drew to resolve it into its constituent R and theta forces: So I get \begin{align} V_r &= - V \cos \theta \\ V_\theta &= V \sin \theta ...
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### What will happen in principle if one tries to push a neutron star?

When we push an object it moves due to the mutual repulsion between the electrons in our hand and the electrons in that object. Since a neutron star contains only neutrons, what will happen in ...
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### Muon and Strong interactions

The strong forces operate up to range of 10^{-15} meter. The calculations for Muon reveal that they can be propagator for distances up to 10^{-14} meter. Why can't I ignore the factor of 10 and call ...
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### How can I calculate the rotational force and motor HP needed to lift a 5lb sheet from a horizontal position to a vertical position from one end?

Essentially, I need to know the following: How do I calculate the rotation force along a fulcrum? Is there an equation? What is the weight of a 5 lb object at the fulcrum if the fulcrum is located ...
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### Symmetry factor and coupling constant in scalar field theory

I am just now starting my particles "education" so forgive me if this is elementary... Looking at interaction terms in a scalar field Lagrangian, I get:  ...
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### Relationship between plasma physics and quark gluon plasma

To what extent do the ideas common in modern plasma physics, such as magnetohydrodynamics, cold plasma models, common types of plasma waves, Maxwell's Equations, etc, relate to the study of quark ...
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### Textbooks on algorithms for the perturbative calculation of High energy physics

For the perturbative calculation of High energy physics, I have known some packages such as FeynArts, FeynCalc, MadGraph, CompHEP, GiNaC, and so on. But I am wondering whether there exists a textbook ...
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### Forces on objects orbiting a black hole?

Firstly, please excuse my elementary knowledge and lack of eloquence when writing about astrophysics. I am a dentist, who occasionally thinks about the how the universe works. I'm both fascinated and ...
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### Why is the current in an electric circuit constant?

Considering electrostatics, suppose we have two charges of equal value and opposite sign and we put electrons along the road between them: We know that the electrical force or field is different from ...
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### Observing a particle over a certain domain

I was just thinking: in Quantum Mechanics, we start out with that whole collapsing business by observing the x position of a particle. I was thinking: why do we have to do that? What if we only ...
The surface area of a first orifice with 2 mm diameter is 3 mm$^2$. The surface area of a second orifice is 5 times bigger from the surface area of the first orifice (15 mm$^2$). How much would be ...