# All Questions

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### why do magnetic field lines leave the north pole and enter the south pole?

suppose we have a bar magnet |S_______________N| ... we can imagine it to be |S-N-S-N-S-N-S-N| So, why do we see the lines leave the north pole and enter the south pole externally? What ...
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### why in a solenoid the magnetic lines resemble to that of a bar magnet?

each loop in the solenoid will have its own magnetic field around it.In that case it wont resemble the magnetic lines formed by a bar magnet...but we see that it is the same...why is it so?
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### Reynolds number and inertial force

The Reynolds number is defined as the ratio of ´inertial´ forces to viscous forces. $$Re = \frac{\text{Inertial Forces}}{\text{Viscous Forces}}$$ Now, viscous forces make sense to me. They are ...
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### Why does a bubble take a spherical shape?

I suspect this has something to do with thermodynamics and the isoperimetric inequality and I'm interested in a mathematical derivation of this result.
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### Results from TLE & SGP4 propagation - don't seem right & need help with interpretation [on hold]

I acquired a TLE of the ISS from internet and used the C++ SGP4 propagator to compute future position and velocity vectors of the Station. I am a little unsure about some aspects of results though and ...
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### Do neutrinos travel faster than light in air?

I read in wiki that the speed of light is 88km/s slower in air than it is in a vacuum. Do neutrinos travel faster than light in air?
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### How can I estimate the density of fog?

I'm working on investigating the effect fog has on drag. I have assumed an air density of $1.225 \frac{\text{kg}}{\text{m}^3}$ for dry air, but I don't know what value for density I could assume that ...
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### Negative charge on capacitor, Kirchoff differential equation with step function

I'm solving a differential equation of the form $$200q'+\frac{200}{3}q=3U_o-6U_6+3U_{12}$$ Where $U$ is the Heaviside step function. $q(0)=0 [Coulombs]$ After solving it, I get that at time $t=18$ ...
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### Atom in a box and collapse of the wave-function

Suppose I have an atom trapped in an optically transparent box. I'm assuming the atom is bouncing off of the walls and not bonding, i.e. the center of mass of the atom experiences a square well. Now ...
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### Electric field from current without Maxwell's law of induction

A long, straight wire carries a current that decreases linearly with time. What is the direction of the induced electric field outside the wire? I would interpret this as follows: a current ...
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### Is it fundamentally possible to capture an orthographic image of the real world?

I thought about asking this question of Photography SE, but I decided that this sort of a fundamental physics question regarding light and dimensional observation, so I decided to cross-post it in ...
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### What does it mean that quantum teleportation can be classically simulated?

Quoting here from Quantum Computation by Neilsen and Chuang : (Gottesman–Knill theorem) Suppose a quantum computation is performed which involves only the following elements: state preparations ...
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### Finding the balance point of a walking stick with a curve (centre of mass) [on hold]

There is a thin walking stick with a straight section of 80cm, and a semicircular handle of diameter 10cm. Let A be the point of the stick which touches the ground (i.e. away from the handle), and B ...
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### How is time real?

Isn't time a human created concept? I mean why hasn't anybody tread on the rationale that there's no time, only physical and chemical reactions which strive to react with each other at a different ...
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### How to determine “timelike”-ness without using a coordinate system?

It has been stated here that: we can say, without introducing a coordinate system, that the interval associated with two events is timelike, lightlike, or spacelike. This assertion appears at ...
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### How does Brake specific fuel consumption vary with Brake mean effective pressure?

I'm aware that there is a certain relationship between brake specific fuel consumption (BSFC) and brake mean effective pressure (BMEP), but I am wondering if someone could explain how each varies with ...
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### energy from nuclear decay prevention [on hold]

A neutron is stable when next to a proton in hydrogen but unstable if two neutrons are present. Could energy be obtained by preventing neutron decay in tritium with a strong magnetic field using Lenz ...
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### Percent error calculations dilemma

I have a set of experimental results for calculating g: 9.82 9.52 10.77 10.39 9.75 9.79 10.13 10.56 10.26 9.84 10.07 9.58 These were taken using a pendulum experiment. My dilemma is that, ...