4
votes
2answers
39 views

Why do some location on Earth have only one tidal maximum per day instead of two?

Most places in the ocean have two high tides and two low tides per "day" (~25 hours). But I remember reading that some locations only have one of each per day. This answer has some great explanations ...
1
vote
1answer
227 views

Calculating jerk vs Fitts law for smoothness

I've tracked the movement of an input method resulting in this dataset. All data is tracked with equal intervals of 100ms. For example an iteration value of 4 means that this is the position of the ...
1
vote
0answers
14 views

Why is Helium so hard to liquify?

By the end of the 19th century all gasses had been liquefied apart from helium (He) [1]. What is it about helium that makes it so hard to liquefy compared to the other gases? And why does it need to ...
-1
votes
0answers
40 views

Electric Circuit Simplification [on hold]

I have been given a problem to simplify this electric circuit diagram: However, as it's quite unusual for me to see resistors connected in such way I couldn't complete the problem even after ...
0
votes
2answers
11 views

The impact of the Oort cloud to change the barycenter of the solar system

Is the Oort cloud changing the position of the barycenter of the solar system? Does it affect in a significant way? How significant?
50
votes
2answers
6k views

If we had a “perfectly efficient” computer and all the energy in the Milky-way available, what number could it count to?

The idea for this question comes from an example in cryptography, where supposedly 256-bit symmetric keys will be enough for all time to come (brute-forcing a 256-bit key is sort-of equivalent to ...
0
votes
0answers
8 views

Eigenstates of position and momentum operators in QM

In Griffiths pages 103-105 "Introduction to Quantum Mechanics" 2nd editiion he states that the eigenfunctions of the position and momentum operators are $$g_y(x) = \delta(x-y)$$ where the eigenvalue ...
3
votes
4answers
82 views

Where does $\hat{P}\psi(x) = -i\hbar \partial_x \psi(x)$ come from?

It's a very basic question, where does the relation $$\hat{P}\psi(x) = -i\hbar \partial_x \psi(x)$$ for any square integrable $\psi(x)$ come into existence? Some texts I found states that the above ...
12
votes
2answers
269 views

Momentum of transverse waves on a string

In general, if a wave carries energy density $u$ with velocity $v$, it also carries momentum density $u/v$. I've seen this explicitly shown for electromagnetic waves and (longitudinal) sound waves. ...
0
votes
0answers
7 views

Solution of Burgers equation in preshock region

According to Hamilton's & Blackstock's Nonlinear acoustics (Section 4.5.4) the solution of Burgers equation of the form: $$ \frac{\partial P}{\partial \sigma} - \frac{1}{\Gamma}\frac{\partial^2 ...
6
votes
1answer
42 views

Signature of $f: \Lambda^2(\mathbb{R}^4) \times \Lambda^2(\mathbb{R}^4) \to \mathbb{R}$, $f(\omega, \omega') = \omega \wedge \omega'$

Define$$f: \Lambda^2(\mathbb{R}^4) \times \Lambda^2(\mathbb{R}^4) \to \Lambda^4(\mathbb{R}^4) \cong \mathbb{R}, \quad f(\omega, \omega') = \omega \wedge \omega'.$$ What is the signature of $f$? ...
0
votes
0answers
7 views

What are good physics engines for modeling elastic materials subject to large deformations?

I'm planning to model soft actuators and I'm not sure whether to use Bullet or something else.
4
votes
2answers
107 views

Gravitational waves in other dimensions

I know this question is purely speculative, as we don't know if more dimensions do exist and also we do not know if gravity is indeed stronger in other dimensions (if they were to exist). But, one of ...
0
votes
0answers
10 views

Why did big bang occur?

Why did big bang occur? Why did it expand from singularity? Was there an alien who disturbed uniformity of universe to start a chain series to expansion?
1
vote
0answers
7 views

master curve of 3D ising model

I am currently doing some Grand canonical monte carlo simulations for LJ particles and my prof has asked to map the normalized probability distribution of density on to a master curve of 3D ising ...
0
votes
1answer
21 views

Does a reflected evanescent wave grow in amplitude?

When considering an evanescent wave travelling in a region between two regions where the solution takes the form of a travelling wave from the maths we have a forwards travelling wave that decreases ...
15
votes
4answers
1k views

How do those T-shirts that change color in the sun work?

When I was a kid, I asked my dad about them and he said (not in so many words) that it was because sunlight and artificial light have different spectrums and they picked colors that reflect only the ...
2
votes
1answer
339 views

Singing: Resonance body open-closed or closed-closed?

Googling yields contradictory results, so here my question: When I sing, my vocal chords vibrate, but my whole body is the resonance body, right? So I would say that when I think about standing waves ...
3
votes
4answers
827 views

The Momentum Operator in QM

I've seen the 'derivation' as to why momentum is an operator, but I still don't buy it. Momentum has always been just a product $m{\bf v}$. Why should it now be an operator. Why can't we just multiply ...
2
votes
1answer
92 views

Frequency of an open air column

Given only the length of an organ pipe to be $2.14 m$, is it possible to find what frequency it vibrates at? If I use the equation $f=\frac{v}{\lambda}$, does the $v$ apply to the speed of sound in ...
0
votes
2answers
27 views

Why electric potential at equatorial point of a dipole is 0?

Well ok I know that electric potential at equatorial point of a dipole is 0. It is a derived conclusion. Q1. But how this can be explained "theoretically"? Another question that electric potential ...
3
votes
1answer
72 views

How to derive end-correction value relationship for open-ended air columns?

According to Young and Freedman's Physics textbook, in open-ended air columns like some woodwind instruments, the position of the displacement antinode extends a tiny amount beyond the end of the ...
3
votes
0answers
53 views

How can I prove that antinodes are present at both open ends of organ pipe mathematically?

I know that for anti node to be formed the magnitude of displacement should be maximum at there. For standing waves in an organ pipe, the boundary conditions are such that anti nodes are formed at ...
7
votes
2answers
86 views
+50

Pressure standing wave nodes at the end of the open side of a tube

I do not understand why standing sound waves can be formed in a one-side or two-side open tube. Consider a one-side open tube. In particular how does the reflection of the wave at the open end occur? ...
4
votes
1answer
38 views

quantum and thermal fluctuations in 1D, 2D, 3D

Why do thermal and quantum fluctuations destroy long-range order in 1D and 2D? Why not in 3D? If the answer is quite elaborated (with many formulas) perhaps a reference would be better. Sorry if this ...
1
vote
1answer
112 views

Quantum field theory with constraint: energy-momentum conservation?

Suppose I have a 2-form field $B$ and a Lagrange multiplier field $\lambda$, then the Lagrangian $S = \int (B \wedge \delta B + \lambda \delta B \wedge \delta B)$ with a Lie derivative operator ...
-4
votes
0answers
23 views

Derivative of an integral help [on hold]

OK, I lied a bit. It's not JUST the derivative of an integral. It's the derivative of a cosine of an integral. Solving the problem of the motion of a simple pendulum under a gravitational field using ...
0
votes
0answers
13 views

Confusion regarding Vacuum fluctuations, Strings & The Casimir Effect

From Wikipedia: Casimir Effect The typical example is of the two uncharged conductive plates in a vacuum, placed a few nanometers apart. In a classical description, the lack of an external field ...
1
vote
1answer
29 views

Why thermal conductivity increases with temperature?

what is the molecular mechanism with which thermal conductivity increases by increasing temperature? at least for metals? I know that heat increases the oscillations of the atoms in the crystal. But ...
-2
votes
0answers
147 views

Galactic binary engine found in the center of the Milky Way? [on hold]

It is accepted science that Sagittarius A* is the black hole in the middle of our galaxy, and motion measurements of Sag A* show that it is more or less stationary relative to our Sun, so why would ...
1
vote
1answer
124 views

Maxwell Stress Tensor at material boundaries

I am trying to grasp the meaning of the Maxwell Stress tensor $T_i^j$ at material boundaries. Concretely, I am trying to calculate the force between two waveguides. The results are given in an article ...
19
votes
4answers
2k views

How did the universe shift from “dark matter dominated” to “dark energy dominated”?

In order to get dark energy to dominate, wouldn't you first need another form of energy to push the expansion until dark energy could dominate? Otherwise I don't understand how the universe could ...
0
votes
1answer
27 views

Fermi energy of electron gas with electrostatic interaction

I have been given the following exam question and am unsure how I would go about solving it: Consider the case of a one-dimensional metal, consisting of a chain of $N$ positive charges $+q$ ...
4
votes
0answers
134 views
+50

Killing tensor and Riemann tensor identity

I know that if we have a Killing vector then it's straightforward to show the identity: $$\nabla_a \nabla_b K_c = R_{cba}^k K_d$$ I'm now trying to show the following identity for a $(0,2)$ Killing ...
1
vote
0answers
13 views

What is vortex row image system in fluid mechanics?

What is vortex row image system in fluid mechanics? I have lot search but I did not find any best answer about this question. Please explain about this topic or give me best link of book or site.
0
votes
0answers
17 views

Reference for Reichenbach synchronisation and non-standard special relativity

My professor introduced in the last lesson a new method for clock synchronisation, which he called "Reichenbach synchronisation". In this new method, two clock A and B synchronise themself with the ...
0
votes
0answers
23 views

Electroweak phase transition

Is it true that when the temperature of the universe was greater than ~200GeV the Higgs did not have any nonzero vacuum expectation value, hence all the particles were massless? So if one calculates ...
3
votes
0answers
20 views

Riemannian metric is a product near the boundary

Let $Y \cup X \subseteq Y'$ be a compact, oriented $(k + 1)$-dimensional manifold with boundary, $\partial Y = X^k$. We know that $X$ has a neighborhood in $Y'$ diffeomorphic to $X \times [0, 1]$. Let ...
1
vote
1answer
124 views

The Fermi Surface of the Free Electron Model for T>0K

For the Free electron model, we can easily describe the Fermi surface at T=0 due to the uniqueness of the Fermi-Dirac Distribution at T=0; below the Fermi-level, a state is definitely filled, above, ...
0
votes
2answers
22 views

Application of Bernoulli's equation to siphon

I'm trying to understand how to use Bernoulli's equation in practice. So I will make an example of where is my confusion. I found this great explanation on Wikipedia about the siphon, but there is a ...
7
votes
3answers
608 views

Cooling down to absolute zero by radiation

Consider a system consisting of a gas, it is put in a container which is permits transmission of all kinds of electromagnetic waves. If this system is isolated and put in a perfect vacuum, and left ...
0
votes
1answer
127 views

Type of spring used in recoil system

What type of coil spring is used in systems like rewind type measuring tape or lawn mower starter mechanism or wristwatch? Is it constant force, constant torque or constant power? And what equations ...
0
votes
0answers
17 views

Does more electromagnetic mass means more electric field is given out?

Does a moving charge give more electric field since it has more electromagnetic mass ? Or Let I have a moving charge with speed 0.9c. kinetic energy hence gained is $m0.81 c^2$. Total energy of ...
1
vote
1answer
36 views

How to measure the mass and balance point of a human forearm?

I've been trying to find this out for about a month now. I'm usually met with humorous but not really helpful comments about chopping my own arm off. I'm preferably looking to do this on a budget ...
-3
votes
1answer
27 views

Do we mean with 'pure energy' the force-carrying particles?

I often read, hear and talk about pure energy. What is meant by this? Does pure energy consists of the forces between matter, or the force mediating particles, like the massless photons and gluon? I ...
4
votes
2answers
45 views

Analysis of a system consisting of a leaking tank of water

The departure point is this problem: A water tank on wheels is moving over an horizontal trail with negligible friction. There is a small opening in one of the walls, at a depth of $h$ below the ...
0
votes
2answers
18 views

Gamma spectroscopy - Nuclide identification

I have a question about what the usual practice is for nuclide identification in gamma spectroscopy. For example, if I see a line at 477 keV, I would write that the origin of this line is $^7Be$. As ...
-1
votes
0answers
8 views

de-rotation of the cosmic microwave background polarization? [duplicate]

0 the polarization of CMB is rotated by effect of cosmological birefringence. then to remove this rotation of polarization, we need to de-rotate this polarization. but I know about this de-rotating ...
-1
votes
3answers
99 views

Composition of energy of electron? [closed]

Mass energy of electron is 0.510 998 9461MeV/ c2 1) Does it include energy of electron due to electric field too? 2) If yes, how much? I am more interested in second part. Links:Here John Rennie ...
7
votes
1answer
213 views

Homotopy proof of the lack of foliation of the Gödel metric

A common proof of the lack of foliation of the Gödel universe, apparently mostly copy pasted from Hawking and Ellis, goes thusly : A closed timelike curve must cross a spacelike hypersurface ...

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