0
votes
3answers
229 views

Animating an Acceleration Vector - Acceleration of object on a crested path in gravitational field

So I was reading in Chapter 3 of my textbook, Sears & Zemanksky's University Physics with Modern Physics by Young and Freedman, 13th Edition, and the discussion took us to a definition of the ...
4
votes
2answers
77 views

How do we know what happens to stars during their life cycle?

It is common knowledge than Sun-sized stars will eventually become red giants, and later they will get gradually smaller again until they cool down into a brown dwarf, and that bigger stars can ...
0
votes
1answer
44 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} ...
8
votes
5answers
2k views

Relativity and Current in Wire

If an observer is stationary relative to a current-carrying wire in which electrons are moving, why does the observer measure the density of moving electrons to be the same as the density of electrons ...
3
votes
1answer
580 views

Coriolis deflection:- is it 4 times if the object is thrown up, compared to a drop?

A particle is thrown up vertically with initial speed, reaches a maximum height and falls back to ground. Show that the Coriolis deflection when it again reaches the ground is opposite in ...
5
votes
4answers
283 views

What will be final velocity of three charges $q$, $q$, $2q$? [on hold]

What will be final velocity of three charges q, q and 2q kept along an eqilateral triangle of side r at infinite distance. All three masses are equal. I tried to conserve Total Energy ...
5
votes
4answers
7k views

Would a pendulum swing indefinitely in a frictionless vacuum?

I am attempting to settle a friendly bet. Would a pendulum swing indefinitely in a hypothetical vacuum (i.e. no air resistance) having a hypothetical frictionless bearing (i.e. no energy lost due to ...
2
votes
2answers
714 views

Angular momentum with respect to the centre of mass

I have been told [Warning: I leave this because it's what I asked and allows to understand the dialogues in the comments, but Azad, whom I thank, has pointed that the formula does not hold in general ...
4
votes
1answer
336 views

Wave packet in curved spacetime

It is known that the classical equation of motion for a scalar field wave packet on a curved spacetime background gives the geodesic trajectory (the e.o.m. is $(\nabla_\mu \nabla^\mu + m^2) \Phi=0$). ...
-2
votes
0answers
18 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
0answers
14 views

What is the mass defect of stable nucleus? [on hold]

What is mass defect of stable nucleus? A-positive B-zero C-negative D-less than unstable nucleus
1
vote
2answers
428 views

Why does this capillary action generator not work?

So I was doing a bit of reading. Apparently the the obstacle to generating energy from the forces driving capillary action is breaking the surface tension at the top of a capillary tube. It is just ...
0
votes
1answer
17 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 ...
-2
votes
0answers
20 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 = ...
-1
votes
6answers
147 views

If gravity is additive, then how does it cancel itself out?

I understand that gravity, as far as we know, is always attractive. Also, it has additive qualities - i.e. the size and strength of the field are proportional to the quantities of mass. This seems to ...
4
votes
3answers
147 views

Does the force between two point charges change when inertial reference frame changes?

The two point charges are as below: Then the Coulomb force between them is: $$F_1=\frac{q^2}{4\pi\epsilon_0 r^2}$$ When the inertial reference frame moves left at $v$(or the point charges move ...
-2
votes
0answers
46 views

Why do you believe in [on hold]

Is it possible that gravity doesn't exist?
1
vote
1answer
20 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 ...
4
votes
0answers
58 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 ...
2
votes
0answers
41 views

Correlation function for ghosts in 2D CFT

In Di Fracenso, page 117, it is explained that the correlation function for two primary fields $\phi_1,\phi_2$ of weights $h_1,h_2$ is constrained to be of the form ...
5
votes
4answers
2k views

Understanding mathematically the free expansion process of an ideal gas

I'm trying to understand mathematically that for the free expansion of an ideal gas the internal energy $E$ just depends on temperature $T$ and not volume $V$. In the free expansion process the ...
0
votes
0answers
10 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
2
votes
2answers
615 views

Dynamic water pressure from flow and diameter

I have to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but, I don't have one. After Googling a lot, I found two formulas allowing to compute the ...
-1
votes
1answer
39 views

Expectation value position of sine wave in infinite square well

Given a neutron (mass$\approx$939 MeV/c$^2$) in an infinite square well of size $a$, the value of the expectation value for position should be in the range $[0-a]$. I know that the general form of the ...
1
vote
1answer
81 views

Crystal field in diamond

The crystal field effect occurs in ionic crystals and causes a splitting of the magnetic quantum levels of the cation. The magnitude of the splitting may be roughly computed by obtaining the potential ...
1
vote
2answers
47 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 ...
-1
votes
0answers
10 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 ...
3
votes
1answer
50 views

Extrinsic Curvature of Surface of Codimension > 1

We can define the extrinsic curvature of a codimension-one surface as $$K_{ab} = q_a^{\phantom{a}c} q_b^{\phantom{b}d} \nabla_c n_d,$$ where $n^d$ is the normal vector to the hypersurface and ...
0
votes
2answers
26 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 ...
2
votes
1answer
434 views

Solve unsteady state Bernoulli equation for flow in a pipe

I am an engineer studying an unsteady-state flow through a pipe. The Pipeline has been cleanly cut into two halves, without deforming the cylindrical form of the pipe, exposing the contents to ...
3
votes
4answers
515 views

How do you find a particular representation for Grassmann numbers?

This question is more general in the sense that I want to know how one finds a particular (say matrix) representation for any object. For the case of Grassmann numbers we have from Wikipedia the ...
2
votes
2answers
1k views

Can an insulator have magnetic poles?

Is it possible to make an insulator have two poles like a magnet? If yes, how to make it?
0
votes
2answers
230 views

Second law of thermodynamics (in terms of entropy)

Is the second law of thermodynamics (in terms of entropy) for closed systems or isolated systems? I thought it must be valid for isolated systems, such as the Universe. But the book Fundamentals of ...
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
41 views

Integrating the geodesic equation to obtain Newtonian energy of test particle

I am studying General Relativity, and have come across a question that I am finding rather intractable: In Newtonian Theory, the energy equation for a test particle in orbit around a point mass ...
0
votes
1answer
23 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 ...
1
vote
2answers
431 views

Repelling force of magnets

What happens if I take two strong magnets and press their like-poles towards each other - does the repelling force created by them equals the force I'm exerting on them or does the repulsion force ...
3
votes
1answer
219 views

How did neodymium magnets get their name?

Like in the question. Why neodymium magnets (Nd2Fe14B) are called "neodymium magnets"? Why not boron magnets? Or iron magnets?
2
votes
1answer
3k views

Why is the mechanical advantage of a wedge = length of slope/ width?

Mechanical advantage is defined as Force Output/Force Input For a symmetrical wedge with the length of the slopes being equal and the width being the distance between the end points, the articles ...
0
votes
1answer
23 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
76 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 ...
3
votes
2answers
44 views

Why does conservation of étendue matter when showing one cannot focus light to arbitrary temperatures?

The latest XKCD What-If post discusses how one cannot start a fire by focusing the light from the moon. The answer is no, for well-established reasons, but the explanation isn't watertight. Maybe ...
1
vote
0answers
16 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 ...
5
votes
2answers
88 views

What evidence is there of the existence of quarks?

What is the experimental evidence that suggests the existence of quarks? How were they discovered? I'm going to assume a particle collider is involved, as it tends to be the case with most subatomic ...
3
votes
1answer
215 views

Force field for calcium ions, potassium ions and water in molecular dynamics

I want to adapt my existing MD simulation so that it can handle these three species. For the interactions of the ions I thought that I would use the coulomb potential, but I don't know what sort of ...
0
votes
1answer
20 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
26 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 ...
1
vote
0answers
24 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
3answers
46 views

FWHM increase with energy (gamma spectra)

Below I have two plots from a gamma spectrum which I've been analyzing. The first plot is between a low energy range, the second between a significantly higher energy range. It is clear that the FWHMs ...
0
votes
1answer
35 views

Is there a way to get the Bethe Roots, that belong to a given eigenvalue of the transfer matrix?

(Quantum) integrable systems, that belong to solutions to the Yang-Baxter-equation, are often solved by the (algebraic) Bethe Ansatz. Solutions to the Bethe-equations lead to the eigenvalues of the ...

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