# All Questions

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### What is the distance to the closest star similar to our Sun? [closed]

My question was inspired by this nice question. But, I recall the phenomenon of strange objects appearing on our sky, and then moving away with a velocity that seems not yet attainable by manmade ...
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### Non-zero potential measured on the surface of an insulator

After driving a screw into an alumina firebrick and applying a 5kV potential, I measured a ~4.5kV potential using a high voltage probe at other locations on the brick surface. Firebrick is generally ...
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### why the electromagnetic wave transmits momentum in the direction of the movement?

Ordinarily a transverse wave does not transmit momentum, as it is the case of the well-known sea wave phenomenon. But the electromagnetic radiation has both fields transversal to the movement of the ...
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### Verification of mass density function in continuum mechanics

I'm having problems knowing where to go with this question: Suppose that a certain material initially fills an open region $\mathcal O\in\mathbb R^3$, with $\Omega:=[-1,1]^3\in\mathcal O$ , so ...
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### Desynchronised pixels in images of the Sun?

NASA published this wonderfull video of Sun from SDO: https://www.youtube.com/watch?v=GSVv40M2aks And it occurred interesting question: Sun is very big sphere. Its so big that it took light 4,6 ...
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### How can diffraction happen in the Hubble Telescope?

I've seen people talking about the angular resolution of the HST is, if using Rayleigh's criterion, equal to: $$\theta = 1.220 \frac{\lambda}{D}$$ My question is, since the diameter of the HST $D$ ...
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### What forces act on an object submerged in flowing fluid in an enclosed environment (i.e pipe)?

Let's say we have a pipe with water flowing through it and obstacle is inserted into the pipe and is rigidly fixed to the inner wall so that it does not get washed away. What forces are exerted by ...
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### Reference for the non-perturbative origin of the baryon masses

I'm looking for nice introductions to the non-perturbative generation of the baryon masses.
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### Detectability of interstellar messages

Recently a debate started whether it is a good idea to send more messages into space in the hope of having alien civilizations receive them. There are some predecessors, most notably the 1974 Arecibo ...
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### Earth's magnetic effect on my magnet

My magnet seems to work independently of, and unaffected by, the Earth's magnetic field, yet the magnetic field of my magnet changes as I introduce some other similar magnets of varied sizes into its ...
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### Does this Hamiltonian have point spectrum?

Consider such a Hamiltonian $$H = - \frac{1}{2} \frac{\partial^2}{\partial x^2} - F x + V(x) ,$$ with $F$ being some constant, and $V(x)= V(x+L)$ being some periodic potential. Does this ...
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### What's the difference between “spectromicroscopy” and “microspectroscopy”? [duplicate]

Both definitions that I found are rather vague. (Related question: What's the difference between microscopy and spectroscopy?)
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### Can surrounding masses influence the speed of time (excluding the time dilation due to gravity)?

https://www.youtube.com/watch?v=ev9zrt__lec @6:22-7:22 If you removed the middle and front spaceships, will the time of the last spaceship flow differently? As this is what it appears to suggest.
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### Is there any material that a magnetic field cannot penetrate? [duplicate]

Is there any way to build an enclosure that protects its contents from magnetic fields more effectively than simply keeping sources of magnetic fields away by the same distance the box would?
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### My electrophorus doesn't work

I have failed in generating charge using electrophorus. The charging material was a balloon rubbed with hair until it became very full of static, as well as a small piece of Styrofoam rubbed with the ...
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### What is thermodynamic equilibrium?

The state of thermodynamic equilibrium is typically defined referring to the system's behaviour in the future. Can the definition be formulated in terms of measurable quantities?
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### Tricky conceptual question: ball sliding and rolling down incline [closed]

We all are familiar with the classic ball rolling down the incline exercise in rotational dynamics. Here is quite a tricky conceptual problem: You have an incline of fixed height, but the angle of ...
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### Determine the value of $g$ with rolling ball

At first, I thought the value of $g$ ($9.8m/s^2$) could be determined simply by placing a ball at the top of a ramp at a known height. The ball was released with no initial velocity, and the final ...
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### Topology of a black hole

How many dimensions are theorized for a black hole, in view of the fact that black holes are not observed directly.