0
votes
3answers
7 views

Dissipate laser light in a surface

Im building a laser target. It consists of a box, with a black plexiglass circle in the center of one of its sides, and a larger white circle around it. The black for the inside shots, and the white ...
0
votes
0answers
6 views

Do metric theories with torsion contradict solar system observations?

Obviously, the answer to this question can be "maybe, if you make the torsion tensor small enough", but my question is, given some "typical" size to the torsion tensor, do the spin-orbit couplings ...
0
votes
1answer
15 views

Circle of light by a laser and wire

I've asked a question before about this phenomenon, see it here Diffraction in Circle of light? or here Laser, wire, and a circle of light But there are some fringes in that circle of light and I ...
0
votes
0answers
4 views

Derivation of the Stuart Landau time dependent amplitude time evolution equation for Hopf or Pitchfork bifurcations

I am studying the Hopf / Pitchfork bifurcations, the ordinary differential equation of which is: $$\dot x = x \ (\rho - x^2)$$ Which is a cubic order equation which describes the time evolution of ...
-1
votes
0answers
13 views

Intersection of two moving objects

There are two objects. The first object moves with speed U1 from known point A to known point B. The second object has speed U2 and starts from known point C. What is the direction the second object ...
2
votes
2answers
21 views

How are determined experimentally the energy levels of the atoms ? How is the calibration done to several decimal points?

I see discrepancy for the absorption edges for the atoms in the X-ray ? For example K-absorption edge of carbon can be anywhere between 282 to 284eV according to different sources. My question is ...
0
votes
2answers
7 views

Is air infiltration a type of convective heat transfer (convection)

I have a building / physics question... A major source of heat loss in homes and buildings is infiltration through cracks (warm air from inside seeping out). Wondering if this falls in the category ...
-5
votes
0answers
17 views

newtonian-mechanics

A 1000Kg helicopter hovers over a forest fire and starts to squirt water downward with a speed of 10m/s at the rate of 40Kg/s. What is the initial upward acceleration on the helicopter when it first ...
2
votes
1answer
33 views

Is UV catastrophe same as IR catastrophe?

I am currently studying quantum physics from Serwey-jewet. Where in the topic of Planck's law, infrared catastrophe is alternatively used for UV catastrophe while explaining how Plancks constant ...
0
votes
0answers
19 views

Does the entropy of the universe change as expansion exceeds the speed of light?

The potential encoded information in a photon that is at the edge of the observable universe would seem to be lost as the universe expands. Does that loss of information contribute to the overall ...
-4
votes
0answers
37 views

The Golden Ratio and universe

It is well known that golden ratio is "almost everywhere", also it is in Milky Way galaxy Can general relativity (or Newton's gravity) explain why the arm of Milky Way galaxy is approximately ...
0
votes
2answers
28 views

How do we know the boundaries of a wavelength?

So the length of a wave is the distance between two compressed regions as shown in this representation of a longitudinal wave: But how do you know exactly where the two points are? Is there a point ...
2
votes
0answers
41 views

Closed timelike curves in the spin-2 gravity formalism

Let's say we take some topologically trivial CTC spacetime, like the Gödel metric : $ds^2 = -dt^2 - 2e^{\sqrt{2}\Omega y} dt dx - \frac{1}{2}e^{\sqrt{2}\Omega y} dx^2 + dy^2 + dz^2$ And then I ...
0
votes
0answers
37 views

Why does specific heat increase with temperature?

Except for monoatomic molecules, specific heat increases with increase in temperature. Why?
0
votes
0answers
43 views

Question on time dilation

When i studied physics we had this example where someone climbes into a rocked flyes into space comes back the time that passes for him one year time on earth 86 years. I think most know what thinking ...
0
votes
0answers
10 views

Is Isochoric compression or expansion possible?

Stirling cycle is made of two isothermal and two isochoric processes. Heat is added isothermally, expansion and compression takes place isochorically, as given by the book. How can a gas be ...
2
votes
4answers
205 views

Does a person inside a falling bus fall to the front of it?

So I was watching Final Destination 5 and something caught my attention. There's a part where a bridge collapses and everything falls apart, so there's this bus that has a person inside (unaware of ...
0
votes
1answer
17 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
-1
votes
0answers
22 views

Would momentum be conserved in teleportation? [on hold]

Defining teleporation loosely as at least quantum tunneling all of your particles and preserving the arrangement. If that doesn't work, assume the mechanisms of the most basic definition of ...
4
votes
1answer
66 views

Why does hitting a cold bag of water freeze?

About 24 hours ago, I bought a box of 30 pieces water ice. I put them in the freezing compartment and when I came from work I was expecting a nice chilling ice. But when I opened the freezer, I saw ...
0
votes
1answer
9 views

The working of rheostat/ potentiometer

I can't grasp the concept of how a rheostat divides potential and acts as a variable resistance in a circuit.I have tried asking my teachers and fellows but their explanation hasn't been satisfactory. ...
0
votes
0answers
16 views

Resonance Stabilization of a mass-spring system

Given point-masses connected by loss-less springs and a specific initial kinetic energy distribution. What mathematical tools exist to analyze the system for resonance stabilization. This problem ...
0
votes
1answer
29 views

Can the entropy of a part of a closed system become less than the initial entropy of the entire system?

I am reading Sir Roger Penrose's book "What came before the Big Bang?". Here, I came across a chapter where he talks about how sunlight provides us energy in low entropy and how through various ...
1
vote
1answer
20 views

Book suggestion for introductory plasma physics

I have an undergraduate background of electrodynamics, special theory of relativity and quantum mechanics. I would like to study plasma physics by myself so please suggest a few introductory books on ...
0
votes
0answers
15 views

Moment of inertia of a connecting rod in a crank-slider mechanism

PROBLEM I am trying to determine the moment of inertia of a connecting rod (conrod) in a crank-slider mechanism. $r$ is the crank radius. $l$ is the length of the conrod. $I_{rod}$ is the moment of ...
0
votes
1answer
22 views

from microscopic to kinetic transport theory

One way to model the dynamics of particles is to find the differential equation of motion of a particle. Of course, this will be nice and easy to do if we have only a few particles (like one-ish, ...
0
votes
1answer
31 views

Matrices as second order tensors proof?

I am trying to proof that all matrices are tensors. I have got to a stage where I need to proof that: $$\gamma_{li} \gamma_{kj}= \frac{\partial q_j}{\partial q_k'} \frac{\partial q'_l}{\partial ...
-2
votes
0answers
38 views

Connecting a mathematical solution to a differential equation with it's physical solution

I have seen this question in a neuroscience course: It is given after the lecture with these and these slides. I have no background in physics. However, I do know how to solve a differential ...
0
votes
0answers
18 views

How redshift-space distortions affects baryonic acoustic oscillations

I have a question with BAO (baryonic acoustic oscillations) and RSD (redshift-space distortions). On large scales, Kaiser effect makes the observed radial separation of galaxies smaller then ...
1
vote
1answer
43 views

Reduction of Earth's Rotation due to increase in humidity

I came to know that, moon is moving away from earth, resulting reduction of Earth's rotation. Similarly, if Earth's humidity increases, water vapor will be move up to the air from water sources, will ...
-1
votes
0answers
7 views

Kinematic Motors in series to flywheel calculation problem

Motor 1 drives a platform at 15 RPM clockwise steady state always 15 RPM. Call the axis of rotation Y. Motor 2 is mounted on this 15 RPM platform and axis aligned thus also Y axis (parallel Axis). A ...
0
votes
0answers
21 views

cosmology - Hubble parameter equation [duplicate]

I have a question. We know that the Hubble constant in the space is a constant, is the same everywhere, but it changes in time, so we don't talk of H0 but H(t). Is there a way, a formula to compute ...
2
votes
0answers
22 views

How much UV light do we have on the ground?

We cannot see it. But suppose each UV photon is replaced by a red light photon, does it make the world look as bright as it is just before the sunrise?
0
votes
1answer
37 views

Transforms in physics? [on hold]

In my studies I have heard of two types of transformations in the physical science 1) the Fourier transform for diffraction and 2) the Legendre transform for thermodynamic potentials. While ...
1
vote
0answers
27 views

Cosmological Bulk Viscosity - is the universe a fluid?

I was trying to make heads of tails of both this paper and the press release about it. The scientists have used bulk viscosity (as opposed to shear viscosity) and popped it into a model and somehow ...
0
votes
0answers
15 views

Expansion in Pauli matrices - coefficient set equal to zero

Lets say you want to calculate the gap parameter $\Delta$ for a superconductor. One approach that is often used is the self-consistency approach for the self energy. Details can be found in this paper ...
0
votes
1answer
20 views

Can a Space tether be made from AmSteel (Samson Rope’s Dynameen)?

AmSteel is a high strength poly-ethylene fiber. Its strength passes that of stainless 316/8 and is considerably less mass per foot. A 4 inch piece could support a length of 160 miles if the ...
4
votes
0answers
54 views

Cleaning a dirty jar

I would like to wash the inside of an almost empty cylindric jar on whose walls there are remains of a sticky substance such as peanut butter. I do this by filling it up with water and then shaking ...
2
votes
1answer
21 views

Will changing the pipe diameter reduce the pressure head loss?

I have this system installed in my house (fig 1), and I'm having problems with the shower. I want to know whether, if I change the pipe shown in red from 1/2" to 1" as shown in fig 2, I will have more ...
2
votes
1answer
41 views

Symmetry of extrinsic curvature tensor

I am trying to solve following problem: In a spacetime of signature (+, −, −, −), let $$ u^au_a = 1, \quad A_{ab} = \nabla_cu_dh^c_{\; a}h^d_{\; b}, \quad h_{ab} = g_{ab} - u_au_b $$ Show that ...
0
votes
1answer
31 views

Is this an inertial frame of reference in relativistic context?

What I've learned from our special relativity lectures is that an inertial frame of reference in relativity is one that experiences no gravitational forces. Also, it is a frame where if a particle is ...
0
votes
2answers
37 views

why in the case of electric field the path of electrons is curved?

I was wondering ,that why in the presence of uniform electric field the electrons are moving in a curved path.
0
votes
3answers
84 views

What is the pace of absolute time

How fast or slow compared to my alarm clock time does time passes in a place where there is no gravitational pull and where you are not moving. I don't know if my question is clear, but is there some ...
5
votes
0answers
75 views

Lorentz transformation of Gamma matrices $\gamma^{\mu}$

From my understanding, gamma matrices transforms under Lorentz transformation $\Lambda$ as \begin{equation} \gamma^{\mu} \rightarrow S[\Lambda]\gamma^{\mu}S[\Lambda]^{-1} = ...
0
votes
0answers
27 views

Transforming matrices using tensor transformations?

Let us say I started with the matrix $$ A= \begin{pmatrix} x & -y\\ y & x \\ \end{pmatrix} $$ And I wanted to use the tensor transformation: $$ \bar ...
0
votes
1answer
24 views

Question about force in transverse waves on a string

In deriving wave equation or power transmission of wave transmitted by a string, it is usually stated (with some assumptions) that the transverse force on a point of the string is proportional to the ...
0
votes
1answer
24 views

Force acting on a dipole placed in a non-uniform electric field

Why does the net force acts in the direction of increasing electric field when an electric dipole is placed in a non-uniform electric field?
2
votes
1answer
35 views

Raychauduri equation for Milne universe

I am trying to solve this kind of problem: Consider the Milne model, i.e., the empty $ \kappa = −1 $ Friedmann model. Verify by a direct calculation that the expansion $ \Theta $ of the unit ...
0
votes
0answers
35 views

QED renormalization: mass and dirac field

Why the mass renormalization $Z_m$ and the field renormalization $Z_\psi$ in QED (MS-renormalized) does not contribute to the beta function computation? From Ward identity, I know that $Z_A=Z_e^{-1}$, ...
9
votes
9answers
2k views

How to emulate 40ft of water

I am part of an underwater robotics team, and our next year's challenge requires us to compete at a depth of 40ft. We don't have any pools nearby to test in, so I want to emulate this 40ft of pressure ...

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