# All Questions

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### Why does cling film (Saran Wrap) cling better to surfaces which are wet or damp than dry?

The product we know in Canada as Saran Wrap is a clear plastic film (no idea of the chemical formulation, believe it to be polyethelene). Among its uses are to cover a dish or bowl. If the hard ...
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### Stability of r-process products

Question: Suppose that an isotope $(Z,A)$ is stable and it has been created by an r-process. What could we say regarding the stability and the creation mechanism for the following isotopes ...
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### Effects of energy loss for a damped wave

I have two questions: 1) When a lightly damped wave losses all it's energy, must it maintain it's wavelength before it dies? 2) When a travelling sine wave is damped, can the peaks be skewed from ...
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### What problems with Electromagnetism led Einstein to the Special Theory of Relativity?

I have often heard it said that several problems in the theory of electromagnetism as described by Maxwell's equations led Einstein to his theory of Special Relativity. What exactly were these ...
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### Why do we consider the application of force as well as bending moment in finding the moments of a beam?

In the standard techniques of beam related problems, solving for moment at any cross section includes counting the torque due to shear force as well as some extra moment, which according to me ...
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### Electromagnetic field and continuous and differentiable vector fields

We have notions of derivative for a continuous and differentiable vector fields. The operations like curl,divergence etc. have well defined precise notions for these fields. We know electrostatic and ...
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### N=4 SYM from Klebanov-Witten field theory

This is with reference to M. J. Strassler's lectures on "The Duality Cascade" pg. 46. I want to see how $\mathcal{N}=4$ SYM emerges when D3 branes, in the KW setup, are placed at smooth point of the ...
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### Can sound produce electricity?

Energies of wind and water can produce electricity. But, can sound energy also be used to produce electricity?
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### $\exp(i\alpha\hat {\bf n}\cdot{\bf \sigma} )=\cos\alpha I+i(\hat {\bf n}\cdot{\bf \sigma})\sin\alpha$

Could anyone tell me $\hat {\bf n}\cdot{\bf \sigma}$ is defined in such way? In the book they have not defined what is $n_z,n_x,n_y$. It is from Quantum Computing: From Linear Algebra to Physical ...
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### Basics of osmosis. What about excluded volume?

I may not understand osmosis very well. Let us suppose two compartments filled with water, separated by a semi-permeable membrane. At equilibrium, both levels are equals. Let us introduce now a given ...
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### Cosmological constant (positive, dS) as SUSY/supertring issue

The "almost" de Sitter expansion of current cosmological model implies a puzzle for supersymmetry (SUSY) and also for string theory. A positive value of the cosmological constant implies a non-null ...
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### Which could provide better energy? [on hold]

This is bothering my mind, clean and efficient source of energy is needed nowadays, in terms of clean energy the most popular is solar and on efficiency its the nuclear, but i heard about this new ...
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### If electrons are magnets do they attract each other?

It is said every electron is negatively charged and so they repel each other but if electrons are tiny magnets(which are responsible for atomic attraction and how solid magnet works) does it mean ...
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### Does a lack of windows protect against shockwave of a nuclear attack?

I know that one of the dangers of a nuclear attack is the shockwave which compresses the air and can cause a pulmonary embolism in creatures in the area of effect. Is the shockwave directional in ...
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### Geodesic curvature and Weyl transformations

The geodesic curvature is given by $$k=\pm t^a n_b\nabla_a t^b,$$ where $t^a$ is a unit vector tangent to the boundary of the string worldsheet and $n_a$ is an outward vector orthogonal to $t^a$. I ...
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### What Non-toxic liquids are the most reflective? [on hold]

I'm looking for a highly reflective liquid that is non-toxic and fairly easy to get hold of. I'm interested in liquids of different viscosity, with the most important criteria being that the liquid ...
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### Work to Create a Vacuum

I'm trying to determine the amount of work required (in Joules) to create a vacuum of a certain pressure in a tube. A pneumatic cylinder will be used to remove the air from the tube to create the ...
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### Notation in a paper on quantum mechanics and gravitation (2)

I am currently reading the paper "Gravitation and quantum mechanics for macroscopic objects" by F. Karolyhazy (1966). The author defines formally rigorous equations in order to describe the decay of ...
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### Sum of 2 Light sources [on hold]

Suppose we have two different sources of light with slightly different wavelength producing a wave in 2 dimensions..their sum in space shouldn't create an envelope with changing color intensity from ...
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### Atmospheric pressure's effect on sound

An argument has been travelling in amongst my friends around this matter and after listening about it for 3 whole days I decided to ask it here. The Question is: Would a high atmospheric pressure ...
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### Equivalent Dose absorption from Na22 source

No idea what exactly the rules are or how I should ask this question, but here's the verbatim quesiton: "A Na$^{22}$ source has an activity of 100 $\mu$C. If you handle the source, how big is the ...
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### Can we represent Simple Harmonic function as triangular waves?

Having studied the topic recently I found out that simple harmonic motion can represented well with sine and cosine functions.Take for example a pendulum swing which could look like : and the ...
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### Books on collision probability and collision processes

Are there any books specifically on collision processes between atoms and molecules and collision probability? I would like to get an overview of the factors that determine collision probability ...
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### What does the notation $\Psi_k/(\Psi_k,\Psi_k)^{1/2}$ mean?

I am currently reading the paper "Gravitation and quantum mechanics for macroscopic objects" by F. Karolyhazy (1966). In his paper, he uses certain notation that I haven't come across before (he also ...
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### Could we tell the difference between population I and II (or even III) neutron stars?

This question is related to thoughts I was having about the mass-radius relationship for neutron stars. Is it unique? Is there a single relationship between $P$ and $\rho$ or is there any chance that ...
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### Why is the Higgs mass renormalization considered a fine-tuning problem, while the electron mass (in QED) isn't?

Don't both masses require infinite corrections in their renormalization procedure? It is my understanding that the electron self-energy in QED increases to infinity with increasing cutoff value on ...
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### Potential difference between point on surface and point on axis of uniformly charged cylinder

Question: Charge is uniformly distributed with charge density ρ inside a very long cylinder of radius R. Find the potential difference between the surface and the axis of the cylinder. Express your ...
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### What is the cause of the large damage by atomic bomb?

I recently read in the Feynman Lectures that when the nuclei like that of uranium which are at the crucial level of balance between strong nuclear forces and electrical repulsive forces are taped ...
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### Does this person get electrified?

Does a person get electrified when his feet are on the floor, his right hand is holding $220~V$ and his left hand holding a piece of wood or any other insulator?
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### When two spheres of equal charge make contact, why does the larger sphere gain more charge?

Suppose that two spheres, $S1$ and $S2$, with radii $R1$ and $R2$ resp. have the same charge uniform charge $Q$ and $R1 > R2$. After they are forced to come in contact, why does $S1$ gain more ...
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### Pseudoforce and friction: confusion

Consider the following situation. A block of mass $M$ is resting on a rough horizontal ground, and a frame is moving towards the right horizontally with an acceleration $a$. Suppose the coefficient of ...
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### Weather and carburetors [on hold]

An automotive engine idling with a closed throttle plate, has roughly twice as much pressure above the throttle plate verses below. Can the highs and lows of carburetor principles be extrapolated to ...
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### If we could build a neutrino telescope, what would we see?

If we could build a neutrino telescope capable of viewing relic neutrinos that decoupled after the big bang, with a similar angular and spectral resolution that is possible now for the CMB, what would ...
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### How to model an apartment's airconditioning?

Background: This reminds situation reminds be of an episode from the The Big Bang Theory, although it is quite different from it. My roommate and I have similar temperature preferences and also share ...
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### Calculating deceleration from a non-constant force [on hold]

As a background : I am trying to design a spring to locate at the end of a zip-line (flying fox) to decelerate a person slowly. I am having some trouble working out the deceleration because it ...
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### How did Maxwell conclude that there was a relationship between light and electromagnetism [on hold]

What is the formula behind it? can you provide both the formula and substitute to show how he did it?
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### What happens to a metal plate in the photoelectric effect?

In the photoelectric effect the electrons are supposed to be removed from the plate if light of appropriate wavelength hits the plate. If electrons are removed, the plate should get ionized ...
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### Why is the cross product between two vectors calculated by the determinant of a matrix

The cross product $\vec{a} \times \vec{b}$ can be written as the determinant of the matrix: \left| \begin{matrix} \vec{i} & \vec{j} & \vec{k} \\ a_i & a_j & a_k \\ b_i & b_j ...
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### Does an electron move in a conductor?

The definition of current is flow of electric charge. But recently I have heard that the electrons cannot move, that they just transmit energy to the other electrons and so on.
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### System and control volume [on hold]

I have a doubt related to the derivation of the general, differential form of the continuity equation. In all text books I referred, it took an elemental "control volume" for the derivation. However, ...
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### Solving for currents in a circuit [on hold]

I need help finding the three listed currents in the figure below. Attached on the bottom is the solution for this problem, however I do not quite understand how they came up with the answers. ...
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### Questions about electromagnetism [on hold]

Are photons units of energy? What is the relation between EM force, EM energy and the photon? Do EM forces carry energy, do they carry the photon (as unit of energy)?
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### Why did the big bang need to produce equal amounts of matter and antimatter?

I've tried to find an answer for this but couldn't find one. Whats the problem with matter being created with little or no antimatter
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### How many atoms make up the average ant? [on hold]

Given an ant is anywhere from three to five milligrams,

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