# All Questions

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### Data on Nuclear Fusion

I'm currently doing a detailed project on Nuclear fusion and it's future. I've found some great books on the subject so thats not a problem. What i'm struggling to find is data more specifically ...
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### Change of temperature in liquid when it is pressurized fast to high pressure

Here's one question I've been thinking for some time: Let's assume that certain volume of water (or any other normal liquid, I'm just thinking how these kind of things should be calculated) is ...
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### Distance between first maxima and first minima in Young double slit experiment

While calculating distance between first maxima and first minima in Young double slit experiment, I used formula for maxima and minimx taking $n=1$ as shown. For first maxima, distance from central ...
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### Are black holes in a binary system with white holes, and are they both wormholes?

What is a black hole? The general explanation is that a black hole is small region in space with such strong gravitational effects that nothing can escape and even light is trapped inside of the event ...
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### Show that boundary layers diffuse out from the plate with speed $\sqrt{\frac{\nu}{t}}$

I was wondering if someone could help me with this problem. I think it's quite simple, but I'm not sure how to do it! An infinite horizontal plate moves with speed $U$ in its on plane relative to ...
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### How does the mass affect the fall time of a parachute?

Why do parachutes with a heavier load fall faster than a parachute with a lighter load?
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### What is Frequecy Pushing/ Pulling in Laser Physics

I heard the term "Frequency Pushing/Pulling" in combination with phenomena like in homogeneous broadening and hole burning but I didn't understand what Frequency Pushing/ Pulling is supposed to mean. ...
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### Calculating collapse factor in the crater equation

In the Crater Equation $$D=0.07C_f\left(\frac{g_e}{g}\right)^{1/6}\left(E \frac{\rho_a}{\rho_t}\right)^{1/3.4}$$ where $\rho_a$ is the density of the impactor, $\rho_t$ that of the object, $g_e$ ...
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### Why is this 4x4 tensor a 16-dimensional representation of SO(3,1)?

In his QFT book "A Modern Introduction to Quantum Field Theory" (http://www.nucleares.unam.mx/~alberto/apuntes/maggiore.pdf, pages 20-21), Michele Maggiore describes the tensor product of the ...
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### The tested scale of classical mechanics

I was reading this, but I was wondering actually how good an approximation is classical mechanics in very large chosen scales? Which makes me would like to ask a question here: to what scale, order ...
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### Motion on a rolling Body

How can an object can continue to run on a rolling circle along the X direction and maintain a balance with specific acceleration.
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### internal torques

In translational motion, for an isolated system, the net internal force acting on the system is zero according to Newton 3 law. But for rotational motion of an isolated system, does the internal ...
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### About to purchase a 3d-printed Keppe Motor Kit for art project - what should I test for?

I'm about to apply for art-grants in order to purchase a educational student toy called a 3d-printed Keppe Motor Kit. Says on their page "Designed with educators and students in mind".. So.. It is ...
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### Diffraction of light around an object & human perception

A wave exhibits diffraction when it encounters an obstacle that bends the wave or when it spreads after emerging from an opening. Diffraction effects are more pronounced when the size of the ...
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### Why does increasing/decreasing the distance between two fringes, decrease/increase the fringe-width in interference pattern?

I am talking about this equation $$w= \frac{D\lambda}{d} \\\ \text{where}\; D= \text{separation between the slits & the screen}\\\ d= \text{separation between the slits}\\w= \text{fringe-width}$$. ...
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### “FTL” Communication with Quantum Entanglement?

Can quantum entanglement make sending a message, whether audio, video, or even Morse code, instantaneous between two points (faster than it could travel normally at the speed of light)? Let me first ...
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### How to predict the distance a ball rolls down a ramp between a certain time period

At t=0 a ball, initially at rest, starts to roll down a ramp with constant acceleration. You notice it moves 1 foot between t=0 seconds and t = 1 second. How far does it move between t = 1 second and ...
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### WIMP dark matter annihilation rate equation (approximation)?

WIMP is a possible dark matter candidates, which self-annihilates. What is the WIMP annihilation rate, as a function of density? Most sources state this scales as $\rho^2$, (density squared), but ...
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I am interested in Lagrangian Mechanics and I want to know why higher derivative theories are inconsistent with the nature. I heard that there is something called Ostrogradsky instability for higher ...
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### Quantum Mechanics, Free Particle with Gaussian Distribution

Assume a free particle of mass $m$ is initially at rest, $v = 0$, which has a time dependent Gaussian distribution $V= \text{expected value of }v$. Write down the expression for the wave function: Is ...
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### Electron double slit, different probabilities of going through each slit

The Problem: Consider a two slit experiment where the slits are not the same. Specifically, consider the case where the probability of an electron passing through one slit is different from that of ...
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### Solving Poisson's Equation in 1-D for a point charge? [migrated]

Ok so I was trying to solve the Poisson's equation for a point charge with a Fourier transform to get the familiar equation. This is what I did so far: So ultimately I am trying to solve this in 3 ...
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### What is the atomic composition of the human body, by volume?

According to Wikipedia, the composition (by atomic percent) of the human body is: 62% hydrogen 24% oxygen 12% carbon 1% nitrogen etc. Question: What is our volumetric composition*? *I get this is ...
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### Are known (“old”) elements being made synthetically using fusion?

Are known ("old") elements being made synthetically using fusion? I hear about research about making new heavy elements, but type "making known elements" on Google and nothing comes up. Are any known ...
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### Is there a difference between 0.18 and 0.180 seconds?

Q. Is there a difference between 0.18 and 0.180 seconds ? In our databases we are collecting timestamps and there are 2 time instants which are the same for the hour, minute and seconds but the ...
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### Charge distribution on a Gaussian surface

In the text, it is said that the skewed distribution of positive charge on the inner wall cannot produce an eletric field in the shell to affect the distribution of charge on the outer wall. Why? ...
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### How can the orbit of a planet having a 3600 year period and a perigee between Uranus and Neptune be computed [on hold]

There is a significant difference between the distance that gravity would move a planet with no velocity and the distance that gravity curves space time for a moving object. The 'fictitious' ...
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### Literature on interferometry

I am looking for a good book/notes etc. about interferometry. I need detailed information about optical as well as atom interferometers with strong emphasize on quantum version for high precision ...
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### What's the physical meaning of a “sphere”, and a pair (or even a series) of “concentric spheres”, in a region with Schwarzschild geometry?

This accepted answer to the question "What is the physical meaning of the Eddington-Finkelstein coordinates?" (PSE/q/91724) prescribes to 1. Enclos[e] the origin of our Schwarzschild spacetime in ...
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### Reaction force explanation?

I heard that reaction force is the total force applied back due to electromagnetic repulsion between the atoms of the thing that exerted the force and the thing that the force was exerted on, so can ...
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### Observers in a Double Slit Experiment

Does it matter what the observer is in the double slit experiment? Could it be anything from an ant to a dog? Has it ever been tried with a non-human observer?