0
votes
0answers
32 views

problem with spin connection term

While working out Kaluza Klein compactification, I am getting the unwanted spin connection term $\omega_{c}^{ac}$ .I have tried to show that this is zero.But I am not quite sure of it. What I tried ...
1
vote
2answers
51 views

How can I understand how $\text{m}^2/\text{s}^2$ is related to $\text{J}/\text{kg}$?

$E=mc^2$ is the famous equation that states the equivalence of mass and energy, with a conversion factor in units of $\text{m}^2/\text{s}^2$. But in my naive mind, the conversion factor of mass and ...
2
votes
0answers
16 views

Approach to model solvent in a lattice: e.g. H2O in NaCl

If a lattice contains a solvent, lets say NaCl and water of crystallisation, what is the condition for a solvent molecule to change it's location? From my current point of view I assume that such a ...
0
votes
1answer
67 views

A question about finding average velocity and average acceleration

I have trouble understanding the following problem's answer: Which of the following relations are true for any arbitrary motion in space? (a) $v_{avg}=\frac{r(t_2)-r(t_1)}{t_2-t_1}$ ...
0
votes
1answer
17 views

Find distance with zero net electric force [on hold]

I am new to the site (and physics!), sorry if this is too elementary or something. I have this problem that I can not solve - perhaps you could help?! Thank you!
1
vote
2answers
71 views

If an asteroid were threatening the Earth, could I deviate it just by jumping on it?

An impact by a 10 kilometres asteroid on the Earth has historically caused an extinction-level event due to catastrophic damage to the biosphere. There is also the threat from comets coming ...
0
votes
0answers
37 views

Group velocity and phase velocity of a wave packet [on hold]

A wave packet in a dispersive medium is represented by the following equation, $$y(x, t) = \cos(1.0x - 5.0t)\cos(0.2x - 0.4t)\cos(0.1x - 0.2t).$$ Find the group velocity and the phase velocity ...
1
vote
0answers
15 views

What is the yield strength of a bar of different cross sections?

Will the yield strength of the combination will be same as that of the rod of uniform cross section?
0
votes
0answers
13 views

I need help using Faraday's Electromotive Equation? [on hold]

I don't understand why the answer in my book is -17.93 mV for Practice Exercise 9.2. I tried solving it on my own but I'm certain that it should be 0 since the dot product is 0. Could someone show me ...
0
votes
0answers
31 views

Error calculation for experimental data

I have the list of experimental values: $$\{w_i \pm \Delta w_i\},$$ where $w_j$ is a mean value and $\Delta w_i$ is an error. I want to calculate the second list $\{a_i \pm \Delta a_i\}$ according to ...
1
vote
0answers
7 views

Dielectric resonance spectroscopy of thin and thick film

How does the technique vary for dielectric resonance spectroscopy for thin film of ~ 3 micrometer and a relatively thick film of 100 micrometer?
0
votes
0answers
12 views

Finding the contained charge in a box, given the $E$-field [on hold]

I'm not sure whether my approach is correct for this problem, it's been a while since I've touched E&M. I thought it best to check, as I'm not sure whether $0$ is the proper answer. I've got a ...
1
vote
0answers
22 views

Calculating relaxation time

When exploring the viscoelastic properties of glassy polymer like PMMA, there are usually two relaxation mechanism: alpha and beta. Usually beta relaxation time varies with temperature following ...
0
votes
0answers
18 views

How to compute Pressure, if acceleration is not given on the Force? [on hold]

I just need clarification on this if my theory is right. This to acquire the pressure applied on a foot of a person. Supposed that the measured mass or weight in the right foot is 50kgs when the ...
3
votes
2answers
42 views

Why is Buoyant Force $V\rho g$?

For a submerged object, buoyant force ($F_b$) is defined as: $$F_b = V_{\text{submerged}} \times \rho \text{ (density)} \times g \text{ (gravitational constant)}$$ Conceptually, the buoyant force ...
0
votes
0answers
41 views

Stern-Gerlach experiment theory question [on hold]

I have an assignment problem which I've been having some difficulty with. i know the answer but I want to know how to arrive at it correctly, and want to know where I've gone wrong. Determine the ...
0
votes
1answer
21 views

Why don't neutral atoms distort the electric field?

Suppose I have a positively charged conductor with a cavity. There's a positive charge inside the cavity and the system has reached electrostatic equilibrium. Then there's negative charge surrounding ...
10
votes
2answers
680 views

What is the square root of the Dirac Delta Function?

What is the square root of the Dirac Delta Function? Is it defined for functional integrals? Can it be used to describe quantum wave functions? \begin{align} \int_{-\infty}^{\infty} ...
1
vote
2answers
45 views

Do all elements spectrum lines fall within the visible light range?

I was wondering if whether we were extremely lucky to have found spectral (absorption) lines of astronomical objects because they fell within the visible light range or if there something intrinsic ...
6
votes
1answer
118 views

Determine if Theory is Unitary from Lagrangian

Question: Given a quantum theory specified with a Lagrangian and the degrees of freedom to be varied, what is the procedure to determine if the theory is unitary or not? Concrete example to aid ...
2
votes
0answers
14 views

Simple gas in cylinder modeling

I want to do a simple (physically plausible but not physically accurate) simulation of a gas in a cylinder as it works on or is worked on by a piston. Wikipedia gives a good example of an adiabatic ...
15
votes
4answers
3k views

Blowing your own sail?

How it this possible? Even if the gif is fake, the Mythbusters did it and with a large sail it really moves forward. What is the explanation?
1
vote
1answer
39 views

What does the first column in the “decay modes” table mean (in Particle Data Group documents)?

As a follow-up to this more general question, what are the values in the first column of each of the "decay tables" in a PDG document describing? What are those things in the first column? Are they ...
0
votes
1answer
43 views

With respect to the doppler effect, are pitch changes sudden or gradual?

Take this excerpt from Wikipedia regarding the Doppler effect: if the siren approached the observer directly, the pitch would remain constant until the vehicle hit him, and then immediately jump to a ...
1
vote
4answers
81 views

Why work $W$ and heat $Q$ are different concepts?

I understand heat as the flow of energy (through radiation, convection or conduction) from one body to another. When I think about conduction (for example) I visualize particles that jiggle a lot ...
1
vote
1answer
44 views

D7 brane profile

I have a doubt about the differential equation leading to the profile of a d7 brane embedded in a 10 dimensional space. According to http://arxiv.org/abs/hep-th/0306018, equation (6), we have the ...
5
votes
1answer
78 views

Why do phase transitions even exist? Why not smooth density change curves?

Why do phase transitions even exist? Why not smooth density change curve? What properties of matter, quantum or otherwise, predicts that matter will undergo phases at different pressures and ...
0
votes
0answers
15 views

Finding $E_{\mathbf p}=f(\hat{H})$ [on hold]

I don't know whether this belongs on the mathematics StackExchange or not but I want to solve $$\hat{H}=\sum_{\lambda}\int d^{3}\mathbf p E_{\mathbf p}\left( \hat{a}_{\lambda}^{\dagger}(\mathbf ...
4
votes
1answer
62 views

Understanding the Particle Data Group review documents

Would someone mind outlining what each piece of semi-structured data means in these images taken of some PDG documents? As a newcomer it is very difficult to interpret the tables. tl;dr This ...
4
votes
3answers
78 views

How to calculate when wheels are better than legs?

We all know that it uses less energy to go by wheeled transport than walking if the terrain is smooth and there are not too many hills. We also all know that when going up steep hills we get off ...
0
votes
0answers
14 views

Sound system and Temperature Effects

You arrange a patio with a sound system. Ignore all sound reflections. If you are at a certain location on the patio, you can find the two lowest frequencies you will experience total destructive ...
-3
votes
0answers
37 views

Diferrence between free electron and the electron in potential well [on hold]

Can you tell me is there any difference free electrons and the electrons in potential well? Is there any energy difference between those two?
8
votes
2answers
902 views

How does an electron move around in an orbital? Is it “wave-like” or random?

When an electron is moving around in it's orbital, is it actually moving around like a wave, like this video shows? (By wave-like, I mean, the "electron" in this video is showing it following a ...
1
vote
4answers
127 views

How does the electron jump across “gaps” in its orbital?

I saw on perhaps COSMOS, and have heard mention from other professors, that electrons sort of "teleport" or something, in their orbital and the quantum level. So looking at the orbitals for a lone ...
0
votes
0answers
13 views

Difference between free electron and the electron in potential well [duplicate]

Is there any difference between free electrons and the electrons in potential well? Is there any energy difference between those two?
0
votes
1answer
14 views

Speakers and Changes in Temperature

Let's say that there is a speaker that oscillates the same way. Now, let's say there is a sudden drop in temperature. I know the speed of sound would drop. But, what will drop, the wavelength or the ...
1
vote
1answer
59 views

Coupled Quantum Harmonic Oscillator

Given the following Hamiltonian for two identical linear oscillators with spring constant $k$ and interaction potential $\alpha x_1x_2$; I was asked to find the expectation value $\langle ...
0
votes
0answers
20 views

Restricted three body problem

I have the restricted three body problem, which corresponds, to the equation $ \ddot a-2\dot b -a= \displaystyle\frac{\partial U}{\partial a} $ $ \ddot b +2 \dot a-b = \displaystyle\frac{\partial ...
0
votes
0answers
16 views

String and Tension Related to Waves [on hold]

You find a string. You create sine waves on it. If you increase the tension of the string, does wavelength increase decrease or remain unaffected? Explain briefly. Can someone check my answer: ...
0
votes
0answers
29 views

Is it possible to limit water flow this way and how is this effect called?

I needed to propose a mechanism to store water and keep water flow at the same level with 100% passive equipment. Here's what I came up with. If you turn a water reservoir upside down and put in ...
1
vote
2answers
56 views

How to get the relation for dependence of anomalous dimension on regularization?

Here is the anomalous dimension: $$ \gamma_{\Gamma}(t, g) = \left[\frac{\partial }{\partial t}\ln \left(Z_{\Gamma}(t , g) \right)\right]_{t = 1}, $$ where $Z_{\Gamma}$ is renormalization factor which ...
0
votes
0answers
18 views

Sound waves travelling in air and the amount of air affected by the wave

If there is a sound wave travelling in the air, will the amount of air transported by the wave be proportional to the intensity? Here is my answer: yes, because as the energy of the wave is related ...
0
votes
1answer
24 views

Horizontal distance covered by an object from an initial height to the ground

We are given: An angle $\theta$ with respect to the ground, its initial height $h_0$ and the final distance $d$. How can we find the initial velocity from this information? I tried a bunch of things, ...
0
votes
1answer
30 views

Reflection - reaction force direction

Let's say object hits a wall. When the object is reflected does the direction of the reaction force caused on the wall looks like the red arrow ? Does that direction depends on how "strong" object is ...
-1
votes
0answers
25 views

addition of a component of a vector to the same vector [on hold]

I am having a problem in the last part of this question-(D).My book says that it is not meaningful. I think that supposing a vector for instance 2i^ has a component 2i^. so when they are added it is ...
0
votes
0answers
17 views

Reason behind the rotation of Earth? [duplicate]

I want to know what is the reason that the Earth rotates on its own axis? What are the forces responsible for the Earth's rotation?
0
votes
0answers
17 views

Action and Reaction on two bodies [duplicate]

If the action and reaction are both equal and opposite then why a body would move? The force exerted by me on the body must be counterbalanced by the force exerted by the body on me.
4
votes
1answer
340 views

Why Do My Fan Blades Produce Color When They Spin?

I've posted a short video on my Dropbox as a visual aid. Whenever I put my fan on Medium speed during the night time, it produces a rotating Blue and Orange color design, despite both fan blades ...
0
votes
3answers
50 views

Transformers and DC voltage

Ok, if I have a transformer with 100 coils of the primary and 200 coils on the secondary and I connect a 9 volt battery to the primary, how many volts should I expect from the secondary coil? I know ...
4
votes
0answers
39 views

String frame and Einstein frame for a Dp-brane

The low energy effective action for $N$ D$p$-branes in the string frame is $$ S_\text{eff} = \frac{1}{16\pi G_{10}}\int d^{10}x \sqrt{-g}\ e^{-2\phi}(R+ 4(\partial\phi)^2+\cdots) $$ where $R$ is the ...

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