# All Questions

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### Will the gravitational pull of air affect the falling rate of an object?

After looking at this question: Don't heavier objects actually fall faster because they exert their own gravity? A thought occurred to me that due to the increased gravitational pull of the ...
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### Aplications of algebraic topology/pure mathematics in nuclear fusion

I am planning on working on an independent research class this fall at a community college. My instructor wants to focus it around pure mathematics/topology/homotopy. I think she has done a phd in ...
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### How does gravitational time dilation work in artificial gravity made by rotating a cylinder?

Concerning gravitational time dilation in artificial gravity (made by a rotating torus like in many sci-fi movies) how would you go about calculating the effect?
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### Intro Mechanics: Finding ball speeds after collision

So I'm reading about conservation of energy, momentum, balls colliding etc. and unsurprisingly there are hundreds of questions in my textbook where essentially they give me some of the variables (m1, ...
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### Electrical resistivity: the effect of adding electrons

Consider a copper wire of fixed length and cross-sectional area, and apply an electric field to the wire induced by a fixed potential difference $V$ across the two endpoints of the wire. The intensity ...
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### Gedanken experiment: Does it collapse to a black hole or not?

Imagine that I am a stationary far-off observer of a massive star that is minutely larger than its Schwarzschild radius (in other words, its on the verge of collapsing). My spacecraft accelerates ...
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### Minima & maxima of Laplace's equation

I don't get the following sentence from David J. Griffiths' Introduction to Electrodynamics (the ambiguous sentence is in bold) Laplace's equation tolerates no local maxima or minima; extreme ...
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### In how lmuch time will the year be exactly 365 days? [on hold]

I understand that the number of days per year has changed throughout the history of the Earth. Apparently there were once over 400 days per trip around the sun. How long will it take approximately ...
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### Books of dynamo theory

I wanted recommendations of dynamo theory pdfs to make a report about magnetic fields of planets and stars with all the math behind it, like vector calculus, Lagrange functions, partial differential ...
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### Faster than speed of light [duplicate]

I was watching a Physics TV show, When someone called Alex Filippenko said that when there was the Big Bang, the Space extended at a speed faster than speed of light. He said that it wasn't against ...
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### Number of classical oscillation modes of a Lattice and number of quantum phonons

In solving the Classical model for lattice dynamics [Rossler pag 38] we find that the lattice admits $$d\cdot N\cdot r = \#modes$$ where $d=$dimension of the problem $N=$ number of atoms $r=$ ...
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### Isn't the aether existant

Before you say I'm wrong consider this, Einstein is supposively the first person to get completely get rid of the various aether models that were proposed. But didn't Einstein actually prove them ...
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### How are standing waves a result of constructive and destructive interferences?

For constructive I can understand. But destructive I can't. I can not picture the shape of two pulses or waves maybe that form the resulting standing wave. The places where waves are canceled just ...
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### how to calculate force needed to launch an object of known mass vertically?

I am going to contract a spring and release it to project an object of known mass to a specified distance upwards(vertically).I want to calculate the needed force to overcome gravity and reach the ...
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### Would a person gain or lose weight after expelling a flatus?

Considering the chemical composition, mass, and pressure range of typical human flatulence, would a person gain or lose weight after passing gas?
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### Detrended Fluctuation Analysis

In the fitting procedure of DFA, how can we understand which order of DFA (Detrended Fluctuation Analysis) (DFA1, DFA2, and higher order DFA) should be applied in the time series?
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### What determines a particles probability of creation?

I know when we're discussing events at a quantum level, we deal in probability and not absolutes. What I'm looking to understand, is when articles I've read on particle physics state a particle has a ...
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### How do I calculate momentum for a particle in a box, using the momentum quantum operator?

For a particle in a one dimensional box with $U(x) = 0$ between $x = 0$ and $x = L$ (infinite Potential well) the momentum for $n = 1,2,3,...$ is given by: $$p_n = \frac{nh}{2 L}$$ The wave ...
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### Variation of quadratic term in modified Einstein-Hilbert actions

In the context of mimetic gravity at some point one try to add to an already modified Einstein-Hilbert action also a term like $$S_\chi=\int\,d^4x\,\sqrt{-g}\frac{1}{2}\gamma\chi^2,\qquad(\star)$$ ...
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### Plane wave solutions of Dirac equation

I'm reading chapter 3 in Peskin on the Dirac equation. First of all, they say since Dirac satisfies Klein Gordon it can be written as a linear combination of plane waves. This is fine. So a general ...
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### Are there any other pairs similar to virtual and normal photons?

Are there virtual particles for every kind of particle there is?
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### Atoms In Space - More Specifically Helium [duplicate]

I've read several articles regarding the limited supply of helium gas on our planet and one that many scientists/engineers require for their research. I suppose if the government were to issue any ...
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### Slingshot Energy into traveled distance [on hold]

If I have a slingshot and I am told that when pulled it has about $E$ joules of energy, how do I compute the height at which an object of mass $m$ would travel if the slingshot is released in the ...
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### Why spinning a pen makes it easier to remove it from the stand?

I have a ballpoint pen stand on my desk. The pens are held inside their caps with the point down, like this one (but not as fancy): If I try to simply pull up one pen, the friction between cap and ...
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### effective mass in a Bohr atom

I was solving a question in a hypothetical situation, in which a carbon atom consists of 6 pions instead of an electrons. Acoording to bohr model of an atom,what would be the ground state energy of ...