# All Questions

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### How are aberration levels measured?

I was reading reading the paper: Predicting subjective judgment of best focus with objective image quality metrics when I come across this statement: Through-focus visual acuity (VA) was ...
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### Newtonian motion in vacuum

A spaceship is moving with constant acceleration in space. suddenly its fuel gets exhausted. Will it continue to move with constant acceleration and its velocity keep on increasing?
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### Material with incredibly small young's modulus [on hold]

I'm looking for a material with a Young's modulus of less than 100 Pa. I've looked at elastomers, but I haven't had any luck. Thanks for your help, I appreciate it.
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### Why does light travels in all directions? [on hold]

My understanding of time, gravity and speed of light: Earth revolves around the Sun. Sun revolves around Milky Way centre. Milky Way also keeps moving. All these movements are caused by gravity. ...
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### Any textbook about non-renormalizability of gravity?

I have learned general relativity in a graduate-level. My knowledge about QFT is very rudimentary. But, I need to learn about non-renormalizability of gravity. I have these questions. Is there any ...
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### Waves interfere in angle equation

If we had two waves perpendicular to each other, with equations: $x=αsin(ωt)$ (1) $y=βsin(ωt+π/2) ==> y=βcos(ωt)$(2) $sin(ωt)^2+cos(ωt)^2=x^2/α^2+y^2/β^2=1$ $x^2/α^2+y^2/β^2=1$ is an equation ...
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### What do people mean with a vev=diag( -2,-2,-2,-2,-2,-2,3,3,3,3)?

For example, in this paper on page 21 the authors write the vev that breaks $SO(10)$ to $SU(4)\times SU(2) \times SU(2)$ $$<54>= 1/5 \cdot diag( -2,-2,-2,-2,-2,-2,3,3,3,3) \omega_s$$ where ...
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### Can everything be described without anything needing to actually “bend”?

Is space bending because gravity actually causes small particles to move differently? If large source of gravity is somewhere are particles extending towards it, creating a "bend" in space? So "bend" ...
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### Find the total energy stored in the network at the time of steady state? [on hold]

Find the total energy stored in this network at the time of steady state.
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### Why is moment of inertia for a point same as a ring

The moment of inertia of a point and ring are both $m R^2$. It is interesting that the formula for moment of inertia is exactly the same for both. Is there any physical reason why this is the case? I ...
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### Three blocks on inclined plane problem [on hold]

I came across this problem on physicsgalaxy.com. My approach: Found limiting friction between 30 kg and 50 kg as 72 N. Found limiting friction between 50 kg and 40 kg as 256 N. Now P+50 sin(37) ...
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### Why is a sine wave considered the fundamental building block of any signal? Why not some other function?

It is mathematically possible to express a given signal as a sum of functions other than sines and cosines. With that in mind, why does signal processing always revolve around breaking down the signal ...
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### Gear ratio in bicycles using rotational motion

When we change the gears of the bicycle we are riding, we change the the disc we are currently at (which are located at the place where we pedal) to some other disc. This means the radius of the ...
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### baryon acoustic oscillation

I have one question about baryon acoustic oscillation. I understand why we should have the baryon-photon fluid sound wave before recombination: Suppose we have a spherical overdense region. This ...
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### Traveling near the speed of light? [duplicate]

Suppose we can travel on a spacecraft near the speed of light, how long it would take for the person on the spacecraft to travel one light year, not to a person observing him/her from Earth, if there ...
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### Detecting molecules in space?

http://www.forbes.com/sites/alexknapp/2012/02/24/nasa-detects-solid-buckyballs-in-space/ I refer to the above article, which mentions that buckyballs "far smaller than the width of a hair" were ...
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### Work Function Calculation with Local Electrostatic Potential

On the Wikipedia site, it describes the work function equation as W = -e\phi - Ef, where phi is the electrostatic potential of a vacuum nearby the surface of the material. So my question is, how can I ...
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### What kind of orbit would be needed to map the surface of a nonrotating planet?

I am not a mathematician and it may even take me weeks to understand the math involved but I have an odd question on orbital mechanics that I hope will be worth the experts' time. I am a hobbyist ...
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### Vibrating water container problem

I am struggling with visualising and understanding the phrasing of this question - cross posted from Math stack exchange since this forum is more appropriate: "A water-filled container is ...
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### can any one please explain in simple terms phase change of reflected light

Phase change is used to explain interference in thin films . The concept is not explained there . Does the change in direction by 180 mean phase change ?
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### error propagation with an integral

My question here is about how to determine the error of an integral given individual uncertainties in two parameters defining the function being integrated. I used a curve fitting function to ...
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### Is Dark Energy and or Dark Matter directly proportional to EMR? [on hold]

Is Dark Energy directly proportional to Electromagnetic radiation (EM radiation or EMR)?
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### On the connection between forces and the principle of stationary action

Feynman tries to account for the relation between the principle of stationary action, which is a statement about the whole path of a particle, and Newton's second law, which is a statement about the ...
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### Velocity change of air down a cone?

Does the velocity of fluids(specifically gasses) change when traveling down a cone from the wide opening to the narrow opening? If so, is there an equation used to calculate the acceleration or ...
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### Rotational dynamics Lagrangian problem

I am trying to construct the Euler-Lagrange equation for a non-inertial reference frame. I have two questions, the first is with regard to the discussion of the transformation properties of the ...
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### When to use lateral magnification vs angular magnification?

What is the essential difference between lateral and angular magnification (like why do we need to use both and when do we use which)? Also, is there a relationship between the two magnifications?
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### Electric field in a non-uniformly charged sheet

So if we have a large sheet that is not uniformly charged and is NOT a conductor, how can I find an expression for the electric field everywhere? Things we know about the sheet: the width is 2b it ...
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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? [duplicate]

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? [duplicate]

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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### How long will it take before the orbit of the earth is 365 days exactly?

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 existent?

Before you say I'm wrong consider this, Einstein is supposedly the first person to get completely get rid of the various aether models that were proposed. But didn't Einstein actually prove them right ...
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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? [on hold]

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? [on hold]

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? [duplicate]

Are there virtual particles for every kind of particle there is?