5
votes
3answers
1k views

What's the difference between Capacitors, Ultra-Capacitors and Batteries

Capacitors are known to hold and release energy very quickly, unlike the slower release that batteries exhibit. If one were to bunch many (1000's of) capacitors together could they function as a ...
1
vote
1answer
397 views

Calculating electromagnetic invariant in matrix form

I'm kind of confused. I want to calculate the electromagnetic invariant $I := F^{\mu\nu}F_{\mu\nu} $, but I'm not sure what is the easiest way to do so. So, I was trying to do it in matrix form, i.e. ...
1
vote
1answer
870 views

Having hard time with Angular Momentum and Parallel axis theorem

I'm having hard time with Angular Momentum and Parallel axis theorem. Please explain these 2 formulas. Is one formula derived from the other? $$J = J_{cm} + R_{cm} \times P_{cm}$$ $$I = I_{cm} + ...
2
votes
4answers
293 views

Equivalence principle question

I understand the equivalence principle as "The physics in a freely-falling small laboratory is that of special relativity (SR)." But I'm not quite sure why this is equivalent to "One cannot tell ...
4
votes
1answer
380 views

why do lightbulbs sometimes unscrew by themselves?

I've seen some light fixtures which exhibit the behavior of lightbulbs gradually unscrewing by themselves.
2
votes
1answer
761 views

Interaction potential in standard $\phi^4$ theory

In this paper, the authors consider a real scalar field theory in $d$-dimensional flat Minkowski space-time, with the action given by $$S=\int d^d\! x ...
0
votes
1answer
455 views

Can a sound mathematical formula become a science theory?

Can a sound mathematical formula become a science theory if it is constructed using a pattern creation process from sense-data, applied to observations by an inductive mapping, in contrast to ...
-1
votes
1answer
141 views

Are more/other colors posible with other dimensions?

Like these impossible colors (yellow/blue and green/red) or these imaginary colors, for example saturated red more intense than pure spectral red can be viewed in ordinary viewing conditions. Can ...
5
votes
2answers
6k views

Can ice have a higher entropy than water?

I've leant that entropy is a state of randomness, and that solids have a more structured form, therefore having less entropy. However, I saw a YouTube comment stating the following: a liquid NOT ...
4
votes
2answers
417 views

Can wind blowing on smooth water create speckle interference patterns?

On a calm smooth lake, or even a large rain puddle, I've seen transient rough patches on the surface suddenly appear and disappear, and sometimes move across the water some distance before ...
4
votes
1answer
674 views

Was the choice of red/green colors for traffic lights a happy coincidence?

All of us have learned since secondary school that the reason we use red in the traffic lights for "Stop" is because it travels the furthest without dispersion. According to wikipedia which cites ...
0
votes
0answers
27 views

Movement of a ball on a curved ramp [duplicate]

Possible Duplicate: What is a natural movement of a ball on a upward curve (the two arrow lines pointing upward) given no external force? http://i47.tinypic.com/mt55s7.jpg -See for image ...
2
votes
0answers
53 views

What name would you give to the method of approximating an arbitrary magnet with many smaller dipoles?

Let's say I had an arbitrarily shaped permanent magnet, with total magnetic moment $M_{0}$. Ways to calculate the magnetic field of this magnet include an analytic solution (if one exists), as well ...
2
votes
1answer
316 views

The definition of entropy

As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only ...
3
votes
1answer
555 views

Expectation values-Wavefunction

I'm a bit puzzled about an excercise in which I have to find the expectation values for position and momentum. Normally this should be pretty easy but in this case I just don't get the point. ...
18
votes
2answers
2k views

Does light reflect if incident at exactly the critical angle?

A lot of textbooks and exam boards claim that light incident at exactly the critical angle is transmitted along the media boundary (i.e. at right-angles to the normal), but this seems to violate the ...
4
votes
2answers
2k views

How to calculate linar velocity of planet orbit?

I try to simulate a solar system with planets (with random mass) placed randomly around a sun with a mass $X \times \text{solar mass}$. The simulation is going well when I use real data ...
1
vote
3answers
2k views

Partition function for quantum harmonic oscillator

Hi guys I'm currently trying to solve a mock exam for an exam in a few days and am a bit confused by the solutions they gave us for this exercise: Exercise: A solid is composed of N atoms which ...
6
votes
0answers
438 views

Are QFT solitons expected to represent standard model particles? Or strings?

Is work on solitons in QFT's focused on finding solutions that could represent the fundamental particles of the Standard Model, or is the work focused on finding particles Beyond The Standard Model? ...
1
vote
2answers
193 views

From differentials to differential equations

Suppose I have a function of time $t$ and position $(x,y)$ such that \begin{equation} p_t \,dt = p \,dy - p_x (1-x) \,dx + p_y \,dy\end{equation} where the subscript denotes a differentiation. In this ...
3
votes
1answer
159 views

Amount of energy to separate Gases - relationship to concentration

I want to understand the efficiencies of separating mixed gases, and for that I want to understand the thermodynamic limit case. Looking at the wikipedia page for entropy of mixing, I find the ...
0
votes
1answer
433 views

Depression of Water Surface by a Needle

Given a needle of mass $m$ modeled by a cylinder of length $l$ and radius $r$ placed on an infinitely large water surface, what is The maximum depression in the water surface; and The equation of ...
2
votes
2answers
2k views

Contact force betweeen 2 objects

Suppose that we have 2 objects next to each other.The object at the left is A and the object at right is B.now we have these situations: 1) we push B to the left. 2) we pull A to the left.(in this ...
11
votes
1answer
1k views

Quantum dimension in topological entanglement entropy

In 2D the entanglement entropy of a simply connected region goes like \begin{align} S_L \to \alpha L - \gamma + \cdots, \end{align} where $\gamma$ is the topological entanglement entropy. $\gamma$ is ...
1
vote
2answers
2k views

Work done in projectile motion

A projectile is shot at some inclination to the ground. It falls at another point having R distance from the initial point on the ground. Is there any work done? If initial velocity vector is $(u\cos ...
10
votes
5answers
2k views

Can low-gravity planets sustain a breathable atmosphere?

If astronauts could deliver a large quantity of breathable air to somewhere with lower gravity, such as Earth's moon, would the air form an atmosphere, or would it float away and disappear? Is there a ...
2
votes
2answers
96 views

Is it part of special relativity that mass possessing energy is more dense?

I was reading http://www.edge.org/3rd_culture/hillis/hillis_p2.html and it says that a charged battery weighs more than a dead one or a rotating object weighs more than a stationary one (i.e. mass ...
7
votes
2answers
262 views

Where can I check a solution to 3D Navier Stokes?

A few years ago I developed a solution to the Navier-Stokes equations and as of yet have not been able to locate a similar version of the solution. I would like to know if anyone has seen a solution ...
12
votes
2answers
2k views

Why are there chiral edge states in the quantum hall effect?

The most popular explanation for the existence of chiral edge states is probably the following: in a magnetic field, electrons move in cyclotron orbits, and such such cyclotron orbits ensure electrons ...
1
vote
0answers
52 views

Heat contained in compressed gas [closed]

I am trying to compute the amount of energy released in the form of heat if I compress 1 cubic meter of Hydrogen to 0.1 cubic meter while submerged in a large body of water of a given temperature - ...
-1
votes
2answers
717 views

What is a natural movement of a ball on a upward curve (the two arrow lines pointing upward) given no external force?

If you drop a ball down a upward curving parabolic ramp, what is the expected movement of the ball? Assume the ball is set into motion with no external force. Would it go all the way from point A to ...
0
votes
1answer
76 views

Any suggestions for units conversion? [duplicate]

Possible Duplicate: Photometer: measured Irradiance L converted to photon rate I am conducting a experiment where stimulus output of $470\ nm$ is measured by a radiometer at $30\ \mu W\ ...
10
votes
4answers
2k views

Can spacetime exist in the absence of matter and energy?

I'm pretty sure Ernst Mach would have said that spacetime cannot exist without matter in it. But I'm also pretty sure that a black hole can be described as a self-sustaining gravitational field, ...
3
votes
1answer
147 views

Does spacetime have momentum?

In what sense can it be said that spacetime possesses momentum? Can an experiment be envisaged to test this question?
1
vote
1answer
116 views

particle accelerator in space

I'm attempting to learn special relativity and i'm having trouble calculating velocity and momentum for each part of the system after interactions. I wanted to know how fast a linear accelerator and ...
3
votes
3answers
692 views

Ising Ferromagnet: Spontaneous symmetry breaking or not?

In explaining/introducing second-order phase transition using Ising system as an example, it is shown via mean-field theory that there are two magnetized phases below the critical temperature. This ...
3
votes
3answers
1k views

Why aren't the graphs for black body radiation straight lines?

We know that a wave which has greater frequency will have low wavelength and high energy. So, by decreasing the wavelength, the frequency and consequently energy (intensity) of that wave will increase ...
4
votes
2answers
182 views

Where might hertz per dioptre actually be useful?

I once came across the strange, artificial unit "hertz per dioptre", which is dimensionally equivalent to "metres per second". Could this unit, by some stretch of the imagination, be used in some ...
1
vote
1answer
735 views

Photometer: measured Irradiance L converted to photon rate

I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source. I wish ...
4
votes
1answer
201 views

On the optics of high-resolution surveillance drones

In this youtube video (which is an except from a documentation I believe) a DARPA development for a high-resolution surveillance camera is presented. This question is regarding the optics that are ...
8
votes
2answers
197 views

Could an ultra-relativistic particle tunnel directly through a stellar mass black hole?

It occurred to me in passing that the Lorentz contraction of a black hole from the perspective of an ultra-relativistic (Lorentz factor larger than about 10^16) particle could reduce the thickness of ...
0
votes
2answers
859 views

Resonant inductive coupling and Schumann resonances

I was reading about WiTricity (http://en.wikipedia.org/wiki/WiTricity) a technology developed by MIT to wirelessly transmit electricity through resonance, and I have this question: Given the ...
2
votes
2answers
385 views

Differentiation and delta function

Need help doing this simple differentiation. Consider 4 d Euclidean(or Minkowskian) spacetime. \begin{equation} \partial_{\mu}\frac{(a-x)_\mu}{(a-x)^4}= ? \end{equation} where $a_\mu$ is a constant ...
1
vote
0answers
43 views

stopping distance [closed]

if it takes a 4 door sedan x amount of feet to go from 65 mph to 45 mph (and i don't know how many feet that is) on a dry straight road, how many feet would it take for a large Mack truck ...
1
vote
0answers
344 views

Apostol or Spivak for mathematical physics? [closed]

I came across many recommendations for both of these books, but I'm not sure which one should I use to study calculus... I know most of the methods used in calculus and I use them frequently, but I'm ...
7
votes
1answer
358 views

Canonical quantization in supersymmetric quantum mechanics

Suppose you have a theory of maps $\phi: {\cal T} \to M$ with $M$ some Riemannian manifold, Lagrangian $$L~=~ \frac12 g_{ij}\dot\phi^i\dot\phi^j + \frac{i}{2}g_{ij}(\overline{\psi}^i ...
8
votes
3answers
768 views

Why is the Yang-Mills gauge group assumed compact and semi-simple?

What is the motivation for including the compactness and semi-simplicity assumptions on the groups that one gauges to obtain Yang-Mills theories? I'd think that these hypotheses lead to physically ...
3
votes
4answers
1k views

Paradox- Object thrown parallel to the ground will never fall down

Suppose an object is thrown parallel to the ground. The gravity acts downward (ie. perpendicular to the direction of motion of the object). The work done by gravity on that object will be given by : ...
2
votes
2answers
204 views

Are there general circuits that differentiate/integrate empirically?

Is it possible to construct simple circuits, that given a time-varying input, produce an output that represents the derivative or integral of the input with respect to time?
2
votes
1answer
81 views

Dark Energy and Conservation of Momentum

IF dark energy was not perfectly evenly distributed(as some theories suggest), in other words if some cubic centimeter had a very small difference from another cubic centimeter, would that imply that ...

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