0
votes
0answers
5 views

phase, group, intantaneous, and average speed/velocity

Is it correct to say phase speed or phase velocity? I've never seen a "direction" associated with phase...only a value. I want to be sure my terminology is correct. Also, how does it relate to the ...
0
votes
0answers
12 views

Can black holes with the same mass evaporate with different speeds?

I am curious about the following observations: (1) For a normal Schwarzschild black hole, it evaporates according to $dm/dt=-1/m^2$; (2) We have eternal black holes which do not evaporate (though ...
0
votes
0answers
11 views

Meaning of $R=0$, $R_{ab}=0$. $R_{abcd}=0$.

First let me state some definition The Einstein tensor is given by \begin{align} G_{\mu\nu} = R_{\mu\nu} - \frac{1}{2} g_{\mu\nu} R \end{align} and note that \begin{align} G^{\mu}_{\phantom{\mu} ...
0
votes
0answers
7 views

Electromagnetic field tensor

How will we derive the component of electromagnetic field tensor by using the electromagnetic field tensor formula; what is the procedure? Can anyone tell me about how I would derive $F_{00}, ...
2
votes
1answer
21 views

How do they find the energy of a photon?

Is the actual energy of a photon ever measured? How is it done? I read that a photon is usually identified by diffraction, that means its wavelength is measured, is that right? In this way we ...
-2
votes
0answers
7 views

What is the mass defect of stable nucleus?

What is mass defect of stable nucleus? A-positive B-zero C-negative D-less than unstable nucleus
0
votes
0answers
4 views

Converting a Bell state to a less entangled state by LOCC

How can I convert a maximally entangled state, $ \frac {1} {\sqrt2} (|00\rangle +|11\rangle) $, to a less entangled state like, $$ cos(\theta)|u_0 v_0\rangle + sin(\theta)|u_1 v_1\rangle $$, by using ...
0
votes
1answer
28 views

A classical explanation of why there is a speed limit in the universe

The question is - is there any flaw in this explanation, or it is the right explanation in general language? Let me break the explanation into two parts - (1) Why there is a certain speed of ...
0
votes
0answers
10 views

Confusion in understanding the derivation of wave speed from Newton's Second Law

In the book 'Principles of Physics' by Resnick,Halliday and Jearl Walker,the opening para of derivation of wave speed from Newton's Second Law is such: Let us consider a symmetrical pulse moving ...
0
votes
1answer
8 views

How to determine the friction constants

We know that the friction is formulated in this form $$F=av+bv^2+Nμ$$ I'm working with an object and surface and I want to find $ a, b, μ $ for them. Can you please give me an experimental method ?
-2
votes
0answers
30 views

Why do you believe in [on hold]

Is it possible that gravity doesn't exist?
0
votes
0answers
28 views

What can be the way of the light [on hold]

All we know that from the Sun to the Earth is comming light. But what can be the motion of the one particle of the light? Its have the source of the light Sun and opened eye on the finish of this ...
0
votes
0answers
10 views

Wave optics physics

When does monochromatic beam of light incident on a reflective surface get completely transmitted.according to the question what exactly the word transmitted means? I'm little bit confused .could you ...
0
votes
0answers
8 views

circular motion pf hc verma [on hold]

a particle of mass m rotates with a uniform angular speed 'w' . It is viewed from a frame rotating about the Z-axis with a uniform angular speed 'z' the centrifugal force on the particle is
0
votes
1answer
11 views

How to apply torque impulse

In the below question, can we apply conservation of Angular Momentum? If not, why? Moreover how do we apply Torque impulse to the system ? The contact force between the cylinders will be normal to ...
-1
votes
0answers
9 views

damage a size D tourch battery will do when thrown forward out a moving vehilce doing 80 kmh

What damage would a size D tourch battery do when thrown hard in a forward direction out a moving vehilce doing 80 km at another vehicle in front of it doing the same speed and would the battery ...
-1
votes
0answers
20 views

Physical Nature of the electric field of the current in a circuit

As most of us know that the electric current in a conductor is due to free electrons moving in the conduction band of metallic conductors. What makes them move ? An electric field of course. ...
0
votes
1answer
36 views

Successor to Copenhagen Interpretation as Orthodox Interpreation of Quantum Mechanics

First, I read the questions FAQ for this and I hope this does not violate the rules. I am not asking for personal opinion, but for observations of hard evidence of trends on this subject. When I ...
2
votes
1answer
15 views

Question about the Blandford–Znajek process

I've been trying to understand the Blandford–Znajek process which explains how Gamma Ray Bursts form, but it's still not clear to me how it works. In this article [ ...
1
vote
2answers
26 views

What is the Benefit of Plotting a Log of Net Force vs. Log of Acceleration Graph?

In preparation for a quiz, I've been going over a set of sample questions. One question in particular asks that if I am to graph the logarithm of the horizontal net force of a system vs the logarithm ...
0
votes
0answers
13 views

event horizon vs apparent horizon ramifications

If the event horizon doesn’t exist in the 2-dimension or 3-dimension time-space - and it doesn’t exist if it can’t be measured or observed - then an apparent horizon would be necessary to reconstruct ...
0
votes
1answer
15 views

How do buoyancy control devices (BCD) work?

I get that having more air decreases density and increases buoyancy. However, we can take the diver-BCD-oxygen-tank to be a single system. How can the pumping of air from the tank into a vest around ...
0
votes
2answers
15 views

How do we determine the pressure at the surface of a star?

Is there any means to do so? I know there are some means to determine the surface temperature.
0
votes
2answers
21 views

Free falling object with air resistance, what's the velocity as a function of time?

So, I'm looking into how velocity can be represented as a function of time when the air resistance is also function of velocity. The force of drag is $$ F_d = C||\vec{v}||\vec{v} $$ where $C$ is an ...
4
votes
0answers
48 views

Are there any open questions in physics that a layman can analyze? [on hold]

In math, there are questions like "What is the minimum number of crosses that this knot has?" which can't fundamentally be solved and simply take a lot of trial and error for an answer. This means ...
0
votes
1answer
15 views

Can we determine the surface temperature of stars other than the sun by using the black body radiation theory?

It is well known that the surface temperature of the sun can be determined by fitting the solar spectrum to the black body radiation spectrum. Is this scheme feasible for other stars? Possibly the ...
0
votes
0answers
11 views

Why does a dynamical gauge field accompany fractionalisation?

I'm trying to understand fractionalisation, of which spin-charge separation is an example. I've read that this is accomplished by introducing a Lagrange multiplier field, which becomes a dynamical ...
0
votes
1answer
20 views

Calculating stopping distance of a car on a slope

I'm having trouble setting up a homework problem properly. We are given the following: A given car can brake to a stop from a speed of 60.0 mi/h in a distance of 123 ft on a level roadway. What ...
2
votes
1answer
63 views

Can a particle have an imaginary mass?

Now, I'm not very involved in the physical sciences, beyond some high-school classes - though I did listen to some college lectures for physics. I was reading "Do Tachyons Exist?" by John Baez, which ...
1
vote
0answers
20 views

Scattering in Black Holes

Let's take your favorite Black Hole and consider the scattering problem for a scalar field around it. Suppose that the Klein-Gordon equation can be separated in the radial and the angular part. Which ...
0
votes
1answer
24 views

Degenerate perturbation theory

I don't understand the part about turning off the perturbation. What is meant by or what is he referring to when he says "upper" and "lower" states. Why must the "upper" state reduce to a ...
0
votes
1answer
18 views

What do I need to calculate UV intensity?

I have a mineralogical UV lamp that I want to use for some research, I only know it's wavelengths. To calculate the µJ/cm3, what else is needed? Distance, time, wattage? Is the value I'm looking for, ...
0
votes
1answer
63 views

Which non-Copenhagen interpretations of Quantum Mechanics have actually produced something useful?

The question has most of it in the name. "Useful" may be interpreted as: measurably different from Copenhagen interpretation and true potentially measurably different and potentially true (i.e. not ...
0
votes
1answer
10 views

Dependance of diffusion coefficient on size?

What's the dependance of the diffusion coefficient on size? More explicitly, suppose I have a particles of characteristic length $l$, dissolved in a liquid. How does $D$, the diffusion coefficient of ...
-2
votes
5answers
56 views

Could it be possible for man to create a star?

If it were possible for us to create a star or a new sun, how could it be done, or how would it have to be done?
0
votes
0answers
27 views

Acceleration of an bubble under the sea [duplicate]

An air bubble arises from the bottom of the sea. Find its acceleration if resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ is cross section area and $v$ is velocity ...
0
votes
1answer
41 views

Navier Stokes : what about angular momentum?

I play with CFD for a while, and suddenly, a transcendantal question raises: :-) Navier Stokes is basically Newton applied on a continuum in Eulerian. For solids, we would consider linear, but also ...
0
votes
2answers
43 views

Is the energy of a collision of two photons the same as one photon hitting a 'wall'?

Special relativity says that the speed of ligt is always the same. So when a photon meets another photon he will encouter it with the speed of light and also the other one. But in case of a wall, the ...
-5
votes
0answers
17 views

The following model describes a jet travelling at 40000 ft at Mach 8. My question is: where do these numbers c0me from?

This model describes flight of an aircraft at 40,000 ft at a speed of Mach 0.8. x˙ = Ax + Bu Matrix A = [-0.0558 -0.9968 0.0802 0.0415 0.598 -0.115 -0.0318 0 -3.05 0.388 ...
-1
votes
0answers
25 views

Motion question [on hold]

I have been struggling to understand how to do this question so some guidance would be great. A racing car of mass 941kg accelerates from 28km/h to 102km/h over a distance of 297m. Frictional forces ...
0
votes
0answers
15 views

How to find frequency from wave equation [on hold]

I have wave equation for vibrating string with damping $M\ddot{x}+C\dot{x}+Kx=0.$ I used this formulae for finding (natural)frequency $\sqrt{\frac{K}{M}-(\frac{C}{2M})^2},$ is it ok?
0
votes
0answers
19 views

Acceleration of an air bubble under the sea [on hold]

An air bubble arises from the bottom of the sea. Find its acceleration if: a) There is no resistance of water b) Resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ ...
1
vote
0answers
22 views

Does a potential of interaction produce also torque?

I have a system of particles (spheres with masses and radii), with $6$ degree of freedom (they are free to move and rotate as they wish). Between each couple there is an interaction potential $V(d)$, ...
1
vote
0answers
17 views

solar energy on a specific location

How to find the amount of solar wattage in any specific place on earh in a monthly manner? by solar wattage I mean the energy recieved from the sun in a squared meters.
0
votes
2answers
27 views

How can space strech a wave?

Because of the expanding of the universe a wave from a far galaxy or star can be streched to more red. But how is space doing that? There must be a kind of 'entanglement' between the wave and space. ...
1
vote
0answers
13 views

Energy and power in a travelling sinusoidal wave

This stuff is driving me crazy. Here: http://galileo.phys.virginia.edu/classes/152.mf1i.spring02/AnalyzingWaves.htm I found that the average kinetic energy per unit length is: $$ \frac{1}{4}\mu ...
-1
votes
0answers
15 views

Problem in statics [on hold]

This is a problem I've been trying to solve for the past days without success. I tried the mathematics forum, since the whole problem consists in finding the value $\beta$ which produces a maximum $P$ ...
0
votes
2answers
23 views

volume of the air bubble in the water

How does the depth affect the volume (the radius) of an air bubble in the water, if the temperature and density of the water are constant. Is there any relation combining this? Can I say that ...
0
votes
0answers
12 views

photometric redshifts - the origin of 1 / (1+ zspec) in photometric accuracy

i have a training sample of sources with known spectroscopic redshifts ($z_{\rm spec}$) and i run a photometric fitting code that uses a template to determine the photometric redshifts ($z_{\rm ...
-2
votes
0answers
18 views

complex waveforms

just wondering if anyone can help me out with a expression I need to find out the phase angle of any hardmonic components present ( relative to the fundamental) of this expression v= 100SIN (100 V = ...

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