# All Questions

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### Do all thing move against gravity with -9.8 meter per second squared acceleration?

If I throw a ball to height h above the earth's surface and then shoot a bullet that reaches the same height but would there be same quantity of acceleration produced in both?
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### Is there a maximum number of neutrons of an isotope?

I wondered whether there is a maximum number of neutrons in an isotope. Or is there no maximum number? So, can an H-75 atom exist?
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### What is Minkowski spacetime?

I was browsing through an article on spacetime when I caught the words Minkowski Spacetime. A Wikipedia search brought me an article too complex for me to totally understand. So what is Minkowski ...
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### Is there any relation between single crystal elastic constants and plastic deformation?

The elastic constants are the tensor coefficient in Hook's Law. Which are valued only in elastic region.But, we are using elastic constants to find the hardness.The hardness is the measure of the ...
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### Is Energy said to do work on the body it is stored in?

Assume a boy on top of the hill, his $potential$ $energy=mgh$. He mostarts to move without pedalling the cycle so is that work being done on it due to the conversion of Potential into Kinetic Energy ...
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### Using formula for work with distance of 0m [duplicate]

Consider this: Wind is pushing a huge rock towards me at with massive force at 2m/s. I push against the rock at equal force so the rock stays still. I am clearly "working" very hard, using a lot of ...
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### Static electricity experiment

My teacher always asks me to do the experiments on static electricity in winter. I don't know why? What will happen if I conduct the experiment in monsoon?
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### A simple question about frequencies, vibrations and engineering

I am a composer that likes science a lot but I am less than amateur at it. I am trying to start understanding how low frequencies (below 100hz let's say) behave. The intent is to find solutions to ...
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### What is a photon? [duplicate]

I'm trying to get a definitive and clear answer to the question of what a photon actually is. Textbooks seem to give quite vague explanations, all starting with Einstein's idea that a quanta is a form ...
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### Would the torque required by a motor differ depending on where it connects to a frame?

Given a motor attached to a flat surface, aligned to the axis of a laptop screen and connected to the screen via an L shaped arm which is also connected to the motor shaft Would the torque required ...
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### Vertical pipe longer than 10m, full of water, top end closed, bottom end under water?

Normal surface air pressure is around 1 bar which is roughly the same pressure of a 10m water column. If I have a pipe full of water that is more than 10m long, top end closed, leave the bottom end ...
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### What is dark matter composed of? [duplicate]

They say that about 80% of the matter in the universe is dark matter -- some unknown substance that has mass. But what is this matter expected or speculated to be composed of? For example might it ...
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### Water tank, circulation, gravity

Is it possible to use gravity alone to make a water circulation system? -a large container filled with water and a hole in the bottom which attaches to a long hose/tube The other end of this ...
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### How does independence of two systems follow from the fact that they are both completely described?

A quote from Landau & Lifshitz (Quantum Mechanics - Non-relativistic Theory, §2): "Let us consider a system composed of two parts, and suppose that the state of this system is given in such a way ...
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### Positronium energy level in QED

I'd like to know if it is possible to compute positronium mass and lifetime from a QED approach. I'm searching for some literature on how to treat resonances in QED (or general QFT) ; most of the ...
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### Accelerating an electron to a high speed

Suppose there are two vertical metal plates. They are separated apart by a small distance. While one is grounded, the other one has a potential of some $V$. Now suppose electrons are produced at the ...
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### Can expectation value be imaginary?

I was solving a problem and the result of the expectation value of an operator came out to be $-\frac{\hbar}{4}$ $i$. Is this result possible? It seems counter intuitive.
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### Does quantum complementarity inherently require ensembles?

If there are two complementary observables, $P$ and $Q$, it does superficially appear as if the only kind of empirical evidence we can get for complementarity has to come from statistical data from an ...
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### How do probabilities emerge in the many-worlds interpretation?

My understanding is that at each quantized unit of time that a split occurs, every possible recombination of particles occurs in the 'objective' universe. If this is the case, what relevance to ...
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### Would a black hole's rotational axis precess in orbit around the sun?

The earth rotates, and its axis of rotation precesses due to the gravitational pull of the sun and moon and other planets upon the mass of the earth. If an earth-sized, rotating black hole was in ...
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### Can mass be uncertain?

If you can have uncertainty in momentum, then wouldn't you have uncertainty in mass and velocity? Why can't mass be uncertain?
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### Resistance of depletion region of PN Junction

It seems that in picture D, the Depletion region is gone because quantitatively we have V= Vj+RI where Vj is the opposite of the built in potential of the depletion region but R is the resistance of ...
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### Special Relativity & QuickSilver from X-Men

In the movie X-Men: Days of Future Past, the mutant character Quicksilver possesses the ability to move very fast. A particularly memorable scene in the movie is one where he runs around very quickly ...
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### How eddy current brakes function

Take the following example: where a rectangular sheet of metal is entering a constant magnetic field at $v \dfrac{m}{s}$. Due to Faraday's law of induction + Lenz's law, we can state that an eddy ...
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### transient process to reach a state described by 'state equation'

we normally use state equation to physcally describe the constitutive relationship between several properties. the state equation is obviously important to connect equations based on first principle. ...
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### Does $\lvert\langle p\lvert\psi\rangle\rvert^2$ have any meaning at all?

I used to think $\lvert\langle p\lvert\psi\rangle\rvert^2$ had the meaning of some likelihood of the particle's momentum being $p$ (within some tolerance interval $\Delta p$). Now I'm just confused. ...
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### geometrical optics

I doing an experiment now. My structure has 700nm periodicity. The surface of the unit structure is sloped at 45 degrees from the normal incidence angle. My laser is 500 nm. I can expect there ...
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### How to obtain the asymptotic behavior of Green's function?

This question arose from Eq.(9.135) and Eq.(9.136) in Fradkin's Field theories of condensed matter physics (2nd Ed.). The author mapped quantum-dimer models to an action of monopole gas in $(2+1)$ ...
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### Can an excited atom have multiple electrons in excited states?

For an excited atom, is it possible for the atom to be excited twice, having multiple electrons in higher energy levels than for the atom in its ground state? If it is indeed possible, what is the ...
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### Did Don Borghi's experiment show that neutrons can be synthesized purely from protons and electrons?

C. Borghi, C. Giori, and A. Dall'Olio published an article entitled "Experimental evidence of emission of neutrons from cold hydrogen plasma" appearing in Yad. Fiz. 56, 147-156 (July 1993) and Phys. ...
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### A problem about Fresnel fringes of electron microscopy

My question is simple: Why do the Fresnel fringes at the edge of a hole in a reticulated carbon film become larger and more widely spaced when the defocus is increased? This occurs whether you are ...
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### What can happen when 2.3*10^28 positrons collide with 2.3*10^28 electrons? [closed]

I'm interested in this question after a writer friend asked me what happens when a human gets bombarded with positrons. Didn't want to post this under scifi because I want more "scientific" answers... ...
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### QFT Perturbative analysis of multiple atom-level quantum computers close to each other

Following up on this question, I'm wondering about electromagnetic interactions perturbation expansions close to a "black-box" quantum computer and modularity of Feynman diagrams in general. Let me ...
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### Why string theorist use the following result? [duplicate]

$1+2+3.......$so on $= -1/12.$ I have seen a few proofs of this result. And I hope most of you are familiar with them. Why string theorist use this ambiguous result in string theory, when assigning ...
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### Filament Lamp equation (Current/Voltage)

I'm starting to work with simple circuits (learning how to measure electromagnetic variables). I have been looking up on the internet for a formula or deduction of a formula that relates the current ...
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In Weinberg's Cosmology, on page 412 eq. 8.1.42 he provides the power spectrum as; $$P(k)=\frac{4(2\pi)^3 N^2 C^2(\Omega_\Lambda / \Omega_M)}{25 \Omega_M^2H_0^4 ... 1answer 69 views ### Can incandescent light bulb can be brighter if fixed power? I found that luminous efficacy of 60 W tungsten incandescent bulb is 14.5 lm/W. Is this value defined by design details listed above or it depends on something else too? Can we design 60 W tungsten ... 2answers 119 views ### Finding Maxwell relations I feel I am missing something about deriving Maxwell relations. I have read http://ocw.mit.edu/courses/physics/8-044-statistical-physics-i-spring-2013/readings-notes-slides/MIT8_044S13_notes.Max.pdf ... 3answers 151 views ### Why do nuclear weapons create a blast wave? As far as I know, in a nuclear explosion the energy is released in the form of radiation (neutrons, gamma rays, alpha particles and electrons), light and heat. There isn't a chemical reaction that ... 2answers 132 views ### Bead on a rotating hoop [closed] This is problem 10.13 from Fowles and Cassiday, 7e. A bead of constant mass m is constrained to slide along a thin, circular hoop of radius l that rotates with constant angular velocity \omega ... 1answer 114 views ### Aether atmospheres http://arxiv.org/abs/1004.1467 claims to have an alternative explanation of the interaction of light around massive objects. Many of the general-relativity-tests such as bending of light near a ... 3answers 162 views ### If a body is at rest at Earth's surface, can we say that its kinetic and potential energy are 0 simultaneously? If a body is at rest at Earth's surface, can we say that its kinetic energy E_{\textrm{kin}}=0, and its potential energy E_{\textrm{pot}}=0 also? Because its velocity v and height above ground ... 0answers 45 views ### Photons and gravity [duplicate] A very powerful laser pointing to the empty space next to small object in space. The photons in the laser beam does not hit the object. Will the small object be gravitationally affected by that laser ... 1answer 52 views ### In a circuit, if voltage is established at both terminals, then how can components use up this voltage? [duplicate] Suppose we use a 9V battery. Then the voltage between these two terminals is 9V. In other words, it would take 9 J of energy to move +1C of charge from the (+) to the (-) terminal by the electric ... 0answers 84 views ### Stability of Mathieu's equation and parameteric resonance I am given the following equation (Mathieu's equation) in my subject of Numerical Analysis :$$ \frac{d^2 x}{dt^2}=-\omega^2(1+\epsilon\cos(t))x $$I am supposed to find those frequencies \omega ... 2answers 45 views ### Do transferring energy and applying force to a body imply same? Do transferring energy and applying force to a body imply same meaning? When we say, "I throw a ball using my pushing force so on the other hand, can I say that I transferred my kinetic energy to the ... 0answers 116 views ### Below what temperature does a semiconductor stop behaving intrinsically? I understand that for an intrinsic semiconductor n=p where n is the electron carrier concentration and p is the hole concentration.My question is how to calculate the temperature at which the ... 2answers 102 views ### Solution to Schrödinger equation I'm trying to solve the Schrödinger equation for a given potential. With some assumptions I end up with:$$\frac{\hbar^2}{2M}\frac{d^2u(r)}{dr^2} = - \left(E - V(r)\right)u(r) Since it's a square ...
Suppose I have some quantum system (like atom) with excitation energy $E_{exc}$ which is homogeneously broadened due to finite lifetime. I shine light with narrow spectrum centred around energy ...