# All Questions

31k views

### Can I compute the mass of a coin based on the sound of its fall?

Other day, I bumped my bookshelf and a coin fell down. This gave me an idea. Is it possible to compute the mass of a coin, based on the sound emitted when it falls? I think that there should be a ...
20 views

### Particle in Oscillating Field

Ignoring quantum effects, what are the dynamics of an electrically charged particular placed with zero initial momentum in an oscillating electromagnetic field, e.g. light?
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### Modeling an Adiabatic Expansion (EES)

How would one model an isentropic (reversible) adiabatic expansion using thermodynamic software in order to determine isentropic work? What I am looking for is an actual pressure-volume curve for the ...
9 views

### Can elastic reflection of some relativistic body be described without introducing notion of field?

Suppose we want to model a non-point particle, e.g. a body of spherical shape, falling on a immobile plane and reflecting from it. I understand that we can't make this body rigid because the ...
49 views

### How can a gas support tensile stresses?

In working through a rigorous derivation of the compressible Navier-Stokes equations, I find that the momentum flux in the X-direction should be driven not only by the normal pressure gradient ...
9 views

### Anomalous Total Transmittance

I am measuring with a Spectrometer UV-Vis-NIR Lambda 900 the total transmittance of a sample made by a sheet of Ethylene vinyl acetate (EVA) between two glasses of 3 mm thickness. I am obtaining an ...
32 views

### What is the difference between Rayleigh scattering and Thomson scattering?

After reading the wiki articles I know, that both Rayleigh scattering and Thomson scattering are elastic processes. But what is the essential difference between those two processes, their cross ...
716 views

### What is the optimal weight for a golf ball?

I am 32 now, and have forgotten the basic physics formulas we used in school. I am sitting with a question that is bugging me. If I had to hit two golf balls of different weight with the same force, ...
161 views

### Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
18 views

### How far can a voice carry through the desert at night? [on hold]

Let's use these conditions: temp = 7C, relative humidity = 10%, air pressure = 85 kPa, elevation = 1500m, shouting at 100dB (not sure if this is a reasonable volume). Given these conditions, what ...
61 views

### Are electric field lines due to Faradays law closed?

Are the field lines of electric field produced by Faraday's law of induction (and assuming $\rho = 0$) necessarily closed? If not what would be a counterexample. If it's true, how to prove it in ...
114 views

### Inductance of a solenoid?

My textbook is using Faraday's law to explain the self inductance that happens in a solenoid with changing current. According to Wikipedia, Faraday's Law is: The induced electromotive force in ...
375 views

### Measuring voltage drop from induced current

I'm having trouble connecting voltage drops and induced current. Imagine you have a triangular loop make up off three resistors. You place this loop in a constantly changing magnetic field. This ...
16 views

### Collision Resolution System Adding Velocity Into System

In my 2-dimensional physics simulation, I have a rectangular rigid body 'a' with infinite mass (the floor), and a rectangular rigid body 'b' with finite mass above it turned at a slight angle. When ...
45 views

### Transmission of waves

How do you know if a wave will transmit when it hits a media boundary? Will a portion of the wave always be transmitted when a wave hits a media boundary? My textbook says part of the wave will be ...
47 views

### Heisenberg formalism of QFT [on hold]

Has anyone tried to develop relativistic quantum theory along the lines of the Heisenberg picture and what's so difficult about promoting time to an operator??
57 views

### How do the wave properties of an electron change with its motion?

How do the wave properties of an electron change with its motion? What about when it is stationary?
31 views

### Simple special relativity problem I can't figure [on hold]

Assuming the earth is located 5 light years from the planet Sirius (measured from Earth), and assuming Sirius is at rest from earth's perspective. In what velocity does a spaceship has to trave ...
439 views

### Dirac, Weyl and Majorana Spinors

To get to the point - what's the defining differences between them? Alas, my current understanding of a spinor is limited. All I know is that they are used to describe fermions (?), but I'm not sure ...
49 views

### How to calculate transmission of photonic band gap fiber?

How to calculate transmission of hollow core photonic fibers (multilayer fiber and 2D band gap fiber)? Which books/article you can recommend ? I see that comsol can do it, but is there a model that ...
23 views

### What effects would we see on Earth if one star of a distant binary system went supernova?

Assume that astronomers on Earth have been monitoring a distant binary star system for a long time (relative to the orbital periods of the binary system) and then they see one star go supernova. Let ...
42 views

### Velocity of a Charged particle in a magnetic field according to Biot-Savart Law

According to Biot-Savart Law, if there is a charged particle in motion, there will be a magnetic field. My question is whether the counterpart of this law also holds true, i.e. if there is a magnetic ...
48 views

### Why are the experiments performed by Felix Ehrenhaft on magnetic monopole and magnetic current so much ignored?

We know about Michelson's experiment. We also know that despite of the null result how many times the experiment was revisited with the hope to get a positive result. Unfortunately, this is not the ...
24 views

### Temperature of Bose-Einstein-Condensate in space

Recently I heared a talk by Bill Phillips, who talked about the coldest temperatures in the universe. Among others, he sayed that the coldest temperatures created at the moment are BECs, which can ...
20 views

### The effect of definition of unit function at t=0 [on hold]

Unit function is defined uniformly everywhere as equal to 1 for t>0 and 0 for t<0. But it is defined variously at t=0. Some define it as 0, some define it as 1 and some others define it as 1/2 ...
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### Why time is considered a dimension?

Why time is considered to be a dimension? And the other 7 (except the 3 dimensions of space, and the dimension of time) dimensions that string theory suggests, why can't they be realized?
56 views

### Latest results in theoretical quantum mechanics? [on hold]

Which are the most important and recent results of theoretical quantum mechanics? If I ask you what it is, what would you say about? Where can I find good articles or resources relating to ...
39 views

### Experiments which show the phenomenon of closed electric field lines

In german physics introductory texts often the following experiment is cited which "shows" that a changing magnetic field can induce an electric field with has closed field lines. Here is a picture of ...
14 views

### Calculate amount of energy based on height of object

How can you calculate the amount of energy an object produces that falls from a particular height? Or water. In an eg i would like to know how can you calculate the amount of electricity water can ...
140 views

### Existence of negative temperatures and the definition of entropy

How negative temperatures can be possible has been treated on StackExchange before (several times in fact), but in light of some recent academic discussion, most of these answers seem to be possibly ...
35 views

### Constancy of speed of light [on hold]

What are the examples for the statement that, the speed of light is constant for all observers irrespective of motion of the observers. I need the examples that can prove Relativity.
30 views

### Existence and Uniqueness of spurious states in Bosonic String Theory

Green, Schwarz and Witten introduce so called spurious states $\phi$, that fulfill $$(L_0 -a )\phi = 0\quad \text{and} \quad (\phi,\psi)=0 \text{ for all physical states }\psi$$ where the $L_n$ are ...