2
votes
2answers
433 views

Non-Linear Density Shell Problem

I'm trying to understand Newton's Shell Theorem (Third) http://en.wikipedia.org/wiki/Shell_theorem However this applies to a sphere of constant density. How is this formulated for sphere of varying ...
1
vote
1answer
626 views

capacitance between widely-separated parallel plates

There's a caveat, which is often ignored, to the "easy" equation for parallel plate capacitors C = epsilon * A / d, namely that d must be much smaller than the dimensions of the parallel plate. Is ...
1
vote
1answer
119 views

Is there a timeline in urban area night temperature?

Fact: We all know that during the day concrete absorbs heat and releases it during the night, making urban areas hotter than rural areas. I observed that after sunset the ambient temperature is going ...
1
vote
1answer
257 views

Changing the capacitance of an object to trigger a capacitive touchscreen [closed]

I'm trying to trigger a human touch in a capacitive touchscreen without the 'human' part. I've noticed that the negative pole of a battery triggers it if you are currently holding it. Or if you use ...
9
votes
1answer
621 views

Geometric/Visual Interpretation of Virasoro Algebra

I've been trying to gain some intuition about Virasoro Algebras, but have failed so far. The Mathematical Definition seems to be clear (as found in http://en.wikipedia.org/wiki/Virasoro_algebra). I ...
3
votes
2answers
304 views

How is the complexification of spacetime justified?

As always the caveat is that I am a mathematician with very little knowledge of physics. I've started my quest for knowledge in this field, but am very very far from having a good grasp. General ...
2
votes
2answers
179 views

Magnification multiplication using telescope arrays?

If we have an array of telescopes attached one after another, would the resultant magnification be multiplied?Also would such a contraption be feasible to make telescopes with amazing magnification?
2
votes
1answer
626 views

Circular equation of motion

I'm reading an article which describes a generation of artificial AKG signal. The article states that they use the following equation of motion: $ \left \lbrace \begin{array} {ccc} \dot x &=& ...
2
votes
3answers
378 views

About symmetry, and about electron density in crystals in particular

The book Introduction to Solid State Physics by Kittel says: "We have seen that a crystal is invariant under any translation of the form T [...]. Any local physical property of the crystal, such as ...
1
vote
2answers
369 views

Problem with forces acting upon a sloped plane

We have a structure that is sloped at 20 Degrees to the horizontal and weights 160N. We then have a force (wind) which is acting along the horizontal plane which has been calculated to be of about ...
3
votes
2answers
2k views

How can we get this formula for Gravitational potential?

I just read the wikipedia page http://en.wikipedia.org/wiki/Gravitational_potential But I don't understand how to get this formula: $$\rho(\mathbf{x}) = \frac{1}{4\pi G}\Delta V(\mathbf{x})$$ Can ...
3
votes
1answer
184 views

Why is the local field algebra $\mathfrak F(O)$ associated with a bounded non-empty open region $O$ of space-time not irreducible?

Let us consider a Wightman field theory for the free scalar neutral field $\phi$, and let $O\mapsto\mathfrak F(O)$ be the net of local von Neumann field algebras. If we take a non-empty bounded open ...
7
votes
1answer
973 views

Representation of the Galileo Group and Central Charges

I've arrived at this question because I've been reading Weinberg's Quantum Theory of Fields Volume I, and I'm in the second chapter about relativistic quantum mechanics. Weinberg discusses the ...
2
votes
2answers
1k views

How thermal imaging cameras work

As far as I see from wiki, 'consumer'-grade(non-cryogenic) thermal imaging cameras use microbolometer sensors to get integrated IR intensity over some 5-12um range. But I had an impression, that ...
0
votes
2answers
261 views

Optical distortions and focus losses calculation

I'm working with a megapixel camera and lens that needs to be focused for an OCR application. In order to measure the focus quality during the set-up, I've built a tool that gives the contrast value ...
1
vote
2answers
288 views

Running: Determine how much more energy is needed per extra kilogram of weight

(I recently asked this on maths but was directed here) I have recently become a runner and having a keen interest in kinematics I'm very interested in the maths/physics of my running. Can someone ...
10
votes
1answer
465 views

how does dynamic casimir effect generate correlated photons

There is a recent paper on arxiv receiving lot of acclaim http://arxiv.org/abs/1105.4714 The authors experimentally show that moving a mirror of a cavity at high speeds produces light from high ...
4
votes
2answers
2k views

How to find the principal point in an image?

I need to find the principal point in an image. Its a point where the principal axis intersects the image sensor. Due to misalignment this point is not at the center of image always(or image sensor). ...
1
vote
1answer
166 views

Is it theoretically possible for the orientation angle of a projectile to remain exactly equal to the orientation of velocity?

This question is sparked by my answer to this question: Is this simulation following real physics? After examining the math, I don't see how it is theoretically possible for the situation simulated ...
0
votes
1answer
233 views

Why electromagnetic waves propagating along x transfers to electron momentum along z?

Why EM waves having only x momentum transfers to electron z momentum? Electron begins oscillating along z, so will not radiate EM waves along z direction, to compensate its z momentum. It seems that ...
2
votes
1answer
819 views

What is wrong with this reasoning on chemical potential?

One definition of the chemical potential is the change of internal energy of the system with respect to a particle of the added substance with the system entropy, molar volume, and all other species ...
1
vote
1answer
670 views

What does cross-track wind mean?

In aircraft literature, what does cross-track and along-track wind directions mean? Please explain in terms of the aircraft's motion relative to the wind direction. I can hazard a guess: along-track ...
9
votes
3answers
323 views

Field created by varying Gravitational field

Changing Electric Field causes Magnetic filed and changing Magnetic Field causes Electric Field. Is there anything similar in relation to Gravitational Field? What sort of field is created by varying ...
1
vote
1answer
270 views

Is this simulation following real physics?

I am trying to simulate a game in Box2D(Physics engine). The game that I am trying to simulate is very simple and can be found here: http://www.makaimedia.com/#/speartoss What I want to know is that, ...
2
votes
0answers
263 views

composition of space expansion and movement as a gauge invariance

suppose i have a space-time where we have one point-like object* which we will call movement space probe or $\mathbf{M}_{A}$ for short, and it will be moving with constant velocity $V^A_{\mu}$ in ...
4
votes
3answers
416 views

How could a particle be isolated to avoid decoherence?

The question aims to this issue : if there is some technological arrangement (or action) to take over the particle/system in order to keep it in a coherent state, then the field, (force or whatever) ...
9
votes
4answers
783 views

Special Relativistic Time Dilation — A computer in a very fast centrifuge

Ok, I've stumbled onto what I think is a bit of a paradox. First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on ...
4
votes
1answer
414 views

Invariance and forms of the Lagrangian

I have been doing Landau and due to its concise style been facing a few problems. I hope you can help me out here somehow. 1)Does the "homogeneity of space and time" essentially talk about the ...
4
votes
4answers
383 views

Understanding Heat

Heat or thermal energy as understood is nothing but motion of molecules of the matter. If the molecules are tightly bound (in case of solids), it is to-and-fro molecular vibrations, otherwise it is ...
2
votes
0answers
143 views

What near-future measurement technique improvements will extend our physical knowledge?

Inspired by the wiki-article on atom-lasers: Another application, which might also benefit from atom lasers, is atom interferometry. In an atom interferometer an atomic wave packet is ...
0
votes
2answers
200 views

How could pinion in automatic quartz watch be rotated at 100K RPM?

Wikipedia article on automatic quartz watch describes the watch mechanism as follows: a rotating pendulum is attached to a pinion and when the wearer moves his hand the pinion is rotated at up to 100 ...
1
vote
2answers
257 views

Gravititonal fields compared to electromagnetic fields - are they infinite in range?

me and my friend has a discussion last night, and he argued that both an electromagnetic field and gravititonal field are infinite in their area of effect, but with diminishing effects as you get ...
-1
votes
1answer
125 views

What is the activity of a planet in a double star system?

If a planet is directly between two stars y distance apart (so it's y/2 from each planet), with velocity x such that x is sufficient to continue orbiting at that distance (y/2), which does it orbit, ...
11
votes
2answers
2k views

Why can we see the cosmic microwave background (CMB)?

I understand that we can never see much farther than the farthest galaxies we have observed. This is because, before the first galaxies formed, the universe was opaque--it was a soup of subatomic ...
7
votes
1answer
357 views

Magnetic susceptibility in 1/eV

In this paper the authors refer to transverse susceptibility $\chi_{ \perp}$ [meV $^{−1}$] I was taught that the magnetic susceptibility is dimensionless. How do I get $\chi$ in the above ...
4
votes
1answer
210 views

Ground-based anti-matter detector on the cheap?

Given today's revelation of the detection of terrestrial gammay-ray flashes (TGF) produced by thunderstorms and the associated pair production of an electron and a positron, how feasible is it to set ...
3
votes
2answers
501 views

What is Time like Quantum Entanglement?

I came across a New Study at : http://arxiv.org/PS_cache/arxiv/pdf/1101/1101.2565v1.pdf . Which talks about Time like quantum entanglement. What does that mean? Comment added by L.Motl: The same ...
2
votes
4answers
2k views

Doppler effect from an accelerating frame of reference

The standard equation for the doppler effect from a frame of reference with constant velocity is $f_0$ initial frequency; $v$ is the velocity of waves in the medium; $v_r$ is the velocity of the ...
10
votes
4answers
4k views

Does it matter how you order your tug-of-war participants?

In a tug-of-war match today, my summer camp students were very concerned about putting the biggest people at the back of the rope. Is there any advantage to this strategy?
4
votes
2answers
487 views

Landau's ambiguous statement about the existence of inertial frames

Landau writes "It is found, however, that a frame of reference can always be chosen in which space is homogeneous and isotropic and time is homogeneous." Does he mean that we can prove the existence ...
4
votes
1answer
596 views

Wave function normalization

A book by C. J. Ballhausen led me to believe that a quick way to check that I performed step operators properly was by observing that the "wave function should appear normalized," but I have found ...
2
votes
1answer
795 views

Does ABS cause a force that resists turning a car into a corner?

ABS systems work by allowing a tire to continue to rotate rather than "locking-up" (stop turning) due to loss of traction with the road surface. A rotating tire can influence the direction of the ...
2
votes
1answer
458 views

Water droplet evaporation due to humidity and temperature

I am conducting an experiment that requires comparison to models for a water droplet's change in size due to evaporation. I've found plenty of papers, but they all seem to require measurement of the ...
2
votes
0answers
133 views

Argument for quantum theoretic conformality of $\cal{N}=2$ super-Chern-Simon's theory in $2+1$ dimensions -Part 2

This is in continuation to what I was asking here earlier - Argument for quantum theoretic conformality of $\cal{N}=2$ super-Chern-Simon's theory in $2+1$ dimensions Or one can look at this ...
1
vote
0answers
112 views

Show that the electric field E in the system at rest is $E=\frac{Q}{4 \pi \epsilon_0 \sqrt{(x^2+y^2+z^2)^3}} (x,y,z)$ [closed]

A body point charge $Q$ moves in relation to the reference system $\Sigma$ according to the law of motion $x(t)=v_0 t$, $y(t)=0$, $z(t)=0$.
1
vote
2answers
3k views

How do I calculate the power consumed by a lightbulb?

I'm studying a lightbulb and its variable resistance, given by the expression: $R(T) = Ro[1 + α(T-T_0)]$, where $R_0$ is the resistance of the lamp at $T_0$. In this case, $R$ is not given by Ohm's ...
1
vote
1answer
156 views

Does 'ring' diaphragm reduce lens spherical abberations?

As I see it, as light comes through approximately same angular area of the lens, it should have less aberrations, and at the same time, it should still have high θ -> diffraction limit should stay as ...
2
votes
2answers
454 views

Wave equations & propagation theories

I'm interrested in making computer simulation but I've run into rather physics oriented problem. I have to choose how to propagate my wave. Though I've found technique called FDTD (finite-difference ...
3
votes
3answers
366 views

Is there any physics behind flocking?

There are many articles published in physics journals about flocking. Is there a physical reason for these phenomena or is it just because physics methods are being used to study collective motion? ...
-5
votes
1answer
244 views

What is a simple physics application of the reciprocal of a square root? [closed]

I learned yesterday that the inverse of square roots is used to calculate the vectors of surface normals in 3d graphics. It seems like such a mind-bogglingly simple idea, and it leads me to wonder if ...

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