# All Questions

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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### 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 ...
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### 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 ...
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### 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 ...
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### 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. ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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, ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...