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44 views

Kinetic energy change in a non-uniform magnetic field?

I have a square loop (sides L) with a current $i$ that produces a non uniform magnetic field which I'll call $\mathbf B$. In the central axis of that loop, I have placed, at a distance $d$ a postive ...
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0answers
18 views

When can the work performed by subsystems not equal the total work by the system?

In his $Thermodynamics$, Fermi mentions the following: “The entropy of a system composed of several parts is very often equal to the sum of the entropies of all the parts. This is true if the ...
-1
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1answer
36 views

How do I obtain the equations for the trajectory of a particle acted by the forces in a vector field?

Suppose we have a vector field, let's say $F(x,y)=(-x,-y)$ and I release a massive particle in the coordinate $(1,1)$. This particle is going to be acted by a force in the direction $(-1,-1)$ and will ...
-1
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0answers
16 views

What are some theories where time emerges from a graph of events?

I'm not really interested in reality, but more so, I'm interested in novel theories or systems or constructions which are inspired by reality, but may or may not accurately reflect reality. I am ...
1
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1answer
64 views

How does Fermi jump to this conclusion in Clausius inequality?

In his $Thermodynamics$, Fermi proves beautifully the following (rephrased): For a system undergoing a cyclic process, $$\oint {\delta Q\over T}\leq 0,$$ and for a reversible cyclic process, it is ...
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2answers
62 views

Why does a layer-like structure occurs in a cold plasma? See pictures

I've been experimenting with cold plasma created by a high voltage source at a frequency of about 23kHz. I observed that sometimes the plasma forms layers within the bulk plasma. Following picture ...
3
votes
2answers
57 views

What will be the effect on the water level? [duplicate]

I came upon this question recently while studying about buoyancy. It goes like this: If an iron block is covered with ice and floats in a tub of water, what will be the change to the water level ...
3
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1answer
59 views

How do we explain the Idea that pressure increases with height in a liquid, With the molecular level (microscopic) reasoning? [duplicate]

We know that in uniform gravitational field, in a liquid, the pressure increases with height. How do we explain this phenomenon with the reasoning at the molecular level? What difference is coming ...
-1
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0answers
29 views

Partial Derivative of the Energy-Momentum Tensor [closed]

How do I calculate the partial derivative of the energy momentum tensor $∂_𝜇 𝑇_{𝜇𝜈}=0 $? and in what conditions its zero? here are the Lagrangian density and $𝑇_{𝜇𝜈}$ formulas, respectively.
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1answer
61 views

Is it possible to determine the motion of a vehicle moving at a constant speed of $0.8c$?

Suppose you are in a rocket with no windows, traveling in deep space far from other objects. Without looking outside the rocket or making any contact with the outside world, explain how you could ...
1
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2answers
26 views

Isobaric Process

I was studying the thermodynamic processes, particularly the isobaric process where the pressure remains constant. While solving a particular question (which I couldn't) I saw that for a gas enclosed ...
3
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3answers
100 views
+150

Is relativistic statistical mechanics “foundationally” relativistic?

Does relativistic statistical mechanics average over particles that exceed the speed of light? This article seems to imply as such: It is interesting to note that the classical and quantum ...
1
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1answer
31 views

SXS gravitational wave data question

I need to do some analysis for a project with the SXS gravitational wave data: https://data.black-holes.org/waveforms/catalog.html but I am a bit confused about the initial conditions of their ...
0
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1answer
31 views

Definition of metric tensor and line elements

I know that the metric tensor $g_{ij}$ is defined as: $$g_{ij} = X_i \cdot X_j$$ where $x_i$ and $x_j$ are the covariant basis vectors ($X_i = \frac{\partial X}{\partial X^i}$) (the definition is ...
-1
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2answers
47 views

Kinetic Energy in a Conservative Field

My problem states that $\vec{F}$ is a conservative field, ie: $F = \nabla \phi$ for some scalar potential $\phi$. $$\begin{align}\vec{F}&=m\vec{a}\\ &=m\frac{\mathrm{d}^2\vec{r}}{\mathrm{d}t^...
-1
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3answers
53 views

Derive gravitational potential energy for this system [closed]

This is on a study guide for my Physics 221 final. I feel like I almost got it but I am off by a sign error. Here is the question: Here is what I got so far: Known: $$F_g = \frac{GMm}{r^2}$$ $$U_g =...
-2
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6answers
116 views

Relativity Of Simultaneity Confusion

I have currently been introduced to relativity of simultaneity with the following thought experiment: Consider a train in which there are two presidents, one sitting at the front and the other at the ...
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0answers
24 views

Noether's current to invariant transformation (scalar theory) [closed]

I need to find the Noether's current in this case: Thank you very much in advance!
1
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1answer
55 views

Is a brachistochrone a straight line in curved space?

Please bear with me, and don't get upset if i have lack in knowledge about spacetime. Brachistochrone: Given two points A and B in a vertical plane, what is the curve traced out by a point acted ...
12
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2answers
1k views

Why isn't current carried through a vacuum?

The empty vacuum of space shouldn't offer any resistance to a travelling electron, and so a large collection of electrons should similarly travel through a vacuum without resistance. As a result, the ...
6
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4answers
665 views

In 4 spatial dimensions, would motion under a central force law be confined to a plane?

In dimension $3$, we have the angular momentum $\omega = q \times v$, and since $$\frac{d}{dt} \omega = v \times v + q \times (F/m)$$ from the fact the force is central (so $F$ is parallel to $q$) we ...
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1answer
44 views

What does an external observer see if you shine a laser pointer while crossing an event horizon?

If I understand correctly, the event horizon of a black hole is the boundary beyond which we cannot perceive or describe any events, and all objects appear to freeze when falling in until their light ...
1
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3answers
42 views

Observed speed of a receding light source

Let’s say there’s a planet 4 light years away from Earth and we send a rocket ship towards that planet at 99.9% light speed. We stay behind on Earth and watch the rocket ship travel towards the other ...
0
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0answers
19 views

VMI image analysis

I used VMI for the photodissociation of O2 and I wonder how I can correlate the radius with the actual velocity of the fragments. Thanks a lot!
0
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1answer
22 views

Noise generated by ball impacting a rigid obstacle

How can I estimate the noise of an elastic non-deformable ball that hits an elastic plate that is simply supported?
2
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0answers
26 views

Normal vectors and induced metric Kerr metric

Consider the Kerr metric given by: $$ds^2 = -(1-\frac{2GMr}{\rho^2})dt^2 - \frac{2GMar\sin^2{\theta}}{\rho^2}(dtd\phi+d\phi dt)+ \frac{\rho^2}{\Delta}dr^2+\rho^2d\theta^2+ \frac{\sin^2\theta}{\rho^2}[...
1
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1answer
30 views

Particle falling into a Kerr black hole

Let's say that a particle starts a radial free fall towards a Kerr black hole with zero initial energy at $r\rightarrow\infty$. The initial angular momentum of the particle is zero ($p_\phi = 0)$. ...
1
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2answers
40 views

Viewing LEDs at great distance

Say I put a satellite in orbit with several LEDs on the outside: red, yellow, blue, white and green. Could I see them from the ground with consumer-grade binoculars or telescopes? If I can see them, ...
0
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0answers
28 views

Transitions between states

In the time dependent perturbation theory, transition between two states requires time dependent hamiltonian, V(t). The question is, why the constant or time independent perturbation does is not ...
0
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0answers
43 views

How does an antiparticle respond to a gravitational field? [duplicate]

A related Wikipedia page provided a little overview. However, here's the question: If an anti-particle acquire a negative mass $m$ in QFT, doesn't $F=ma$ indicate that the anti-particle will ...
0
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0answers
28 views

Interaction (Dirac) picture and time dependent perturbation theory

Why in many, if not all, references that discuss the time dependent perturbation theory, they start the discussion with the interaction (Dirac) picture, although, what we need is only solving the time ...
2
votes
1answer
35 views

Off-diagonal elements of the inertia tensor and its eigenvalues [duplicate]

Given a certain rigid object, its inertia tensor $\tilde I$ is given by $$\begin{pmatrix} I_{xx} & I_{xy} & I_{xz}\\ I_{yx}& I_{yy}& I_{yz}\\ I_{zx}& I_{zy}& I_{zz} \end{...
-1
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0answers
31 views

Where can i practice my analytical mechanics?

Does anyone know a good source ? Personally looking for Q & A but cant seem to find
1
vote
1answer
36 views

Thermal expansion of a rectangular metal shape

This question is inspired by this interesting answer which left me somewhat uncomfortable for the following reasons: Suppose we have the following notched metal shape: Following the linked answer, ...
0
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0answers
11 views

Projection of speed of particles moving close to speed of light [closed]

Let's describe the velocity of the massless particle in two-dimensional plane with an absolute value $v$ and direction $\phi$. How fast should travel the particle in direction $\phi+\Delta\phi$ so ...
0
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0answers
11 views

What form(s) of radiation are least attenuated by the atmosphere?

Given the composition of Earth's atmosphere, what is the most efficient way of wirelessly beaming energy from the stratosphere down to the surface?
0
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1answer
16 views

MOSFET Mobility

The surface mobility is lower than the bulk mobility because of surface roughness scattering What is surface roughness scattering? How does it affect the mobility?
1
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0answers
25 views

Von Neumann entropy for non-interacting systems

I am trying to compute the von Neumann entropy for a system described by a non-interacting Hamiltonian: $ H = \sum_\alpha\epsilon _\alpha N_\alpha $ where N is the number operator $N_\alpha = a^\...
-1
votes
0answers
11 views

How to find to which hydrogen spectrum does electron belong [closed]

Suppose electron jumps from 4th excited state to first. To which series these lines corresponds. ( Lyman , balmer , paschen , brackett , pfund)
0
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0answers
63 views

Find motion equation for two solids connected by a spring

I am trying to find a way how to solve a second order inhomogeneous coupled ODE. My example problem is the following: Two solids are connected with a spring (which only transfers force in x direction)...
0
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2answers
48 views

Power of a river

I'm trying to calculate the power of the Mississippi, using the section of the river as it passes through New Orleans. I have the flow rate of a river, turned into a mass flow rate of $16,992,000 kg/s$...
0
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0answers
20 views

Why is $\Delta_r G^0$ temperature dependent in the van 't Hoff equation?

One can derive for a equilibrium reaction between ideal gases $$\sum_i \nu_i R_i \leftrightarrow \sum_i \nu_i P_i $$ the expression $$ \Delta_r G^0=-RTln(K) \quad \textrm{where} \quad K=\frac{\Pi_{\...
16
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11answers
2k views

Is concept of entropy really indispensable? Especially when the concept of potential energy can serve the purpose?

We see that all the natural systems aspire for minimum potential energy state and we also see that all the natural systems also aspire for maximum entropy state. Now from this understanding it seems ...
-1
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0answers
15 views

If the alignment of one tyre of a car is Disturbed [closed]

If the alignment of one tyre of a car is Disturbed. Then to reduced the damage of tyres due to friction the speed of car should be decrease or increase.
0
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0answers
17 views

Photon-phonon scattering problem

I have to calculate the following: a) The speed of the acoustic phonons b) Which phonons(frequency and wavevector) can be observed for scattering angles between 0° and 180° and how much of the ...
-1
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0answers
32 views

Want to start general relativity from a book for beginners [duplicate]

Want to start general relativity from a book for beginners. please suggest a book for beginners.
-3
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0answers
51 views

If a Black Hole is Travelling Faster than the Speed of Light, Would its Contents Leak? [closed]

Matter must move past the speed of light to escape the Event Horizon of a Black Hole. Assuming that Tachyons exist and have significant gravitational force, we shall imagine that a Black Hole is being ...
0
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1answer
59 views

Quantum mechanical reasoning to seeing colours

I don't know if I am writing but this is how I understand it: If I am looking at blue paint... White light falls onto the paint, the electron in the atoms of the paint absorbs all white light and ...
-1
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2answers
33 views

Is the E field generally conservative outside the cases when vector potential goes to zero?

In Ronald Wangsness' "Electromagnetic Fields" book, he states that $\textbf{E}$ generally depends on both a scalar and vector potential in the form, $$\textbf{E} = -{\bf \nabla}\Phi -\frac{\partial \...
0
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1answer
16 views

Motion of a current carrying conductor

When a current carrying conductor is placed inside magnetic field, what motion does it take? Does the motion not occur and only Hall emf is obtained. Or if there is a motion due to Lorentz Force, ...

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