# All Questions

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### Calculating resultant force along vertical axis when using smartphone accelerometer

I'm making an app which is using accelerometer to automatically detect damages on the route while driving. To estimate if damage occurred or not I'm using accelerometer (acceleration along vertical y ...
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### Why is it misty at such high temperatures as per weather reports?

I am residing in New Delhi (pardon me for any irrelevant data I might include), and I noticed a really interesting thing. It's an average $30^{\circ}C$ out here, and yet, most/some weather ...
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### What conditions are necessary for Birkeland currents to form?

If charged particles flow through non-magnetised space will they form Birkeland current? Or can such currents only form along existing magnetic field lines? Part of the reason I ask is this: http://...
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### Proof of minimum distance between object and image of a convex lens image being 4*focal length

I can prove that the minimum distance between an object and its image, through a convex lens is 4*focal length, if I assume that the distance between the object and the lens is the same as the ...
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### Why are topological phases described by modular tensor categories?

After some reading, I have an inuitive idea what topological phases of matter are. But where is the connection to modular tensor categories? Is there fundamental literature where this is covered? ...
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### What is the gravitational field inside a hollow spherical cavity embedded in a solid sphere? [duplicate]

Imagine a solid sphere of radius $R$. From the inside of this sphere we remove a smaller sphere of radius $r$. The sphere can be situated anywhere inside the massive sphere. How does the gravitational ...
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### What are the odds of finding an electron a long way from an atom? As in metres away?

Pretty self-explanatory, heard that there is a chance that you might find an electron on the other side of the universe, just wanted to know.
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### Exact expression for the ground state energy in the 1D Bose-Hubbard model

I heard that Bose-Hubbard model is exactly solvable in 1D. What is then expression for the ground state energy $E_{0}(N, M, ...)$ as a function of total number of particles $N$, number of lattice ...
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### How to find Tangential/Radial/Angular Velocity for motion in any curve?

Is the radial velocity responsible only for changing distance between objects and the component perpendicular to it only for change in direction? If so why? Please try to give a different explanation ...
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### Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
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### What causes more damage, a head-on car crash at 30km/h or one car at 60km/h crashing into a stationary one?

Which will cause a greater impact? Two identical cars colliding head on (in opposite directions), each going at 30km/h OR One car travelling at 60km/h colliding into a stationary car (for the ...
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### Physics of detection of coherent light in an incoherent background using the more compact Fabry Perot interfeometer?

I read University Of California Berkeley Professor J. Bokor's Chapter 7 course notes , shown below as an imgur image , on Temporal Coherence tonight. I am sending an email to Professor J. Bokor ...
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### Charge balance and Bogoliubov quasiparticles

Before trying to understand charge imbalance in superconductors (eg Hübler et al., Phys. Rev. B 81, 184524, Quay et al., Nature Physics 9,84–88 (2013)) I thought I had better check I understand the ...
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### Torque direction meaning

I apologize if this question is dumb, but I've looked all over for a straightforward answer and either I can't find one or the terms are too complex for me to understand. I have only a rudimentary ...
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### What on Earth is this drawing of Venus?

The Wikipedia article for Venus's alleged moon Neith has this picture: And a tantalizing remark regarding paramecia (vandalism?). I know the grey ball is supposed to be Neith, the white is Venus, ...
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### Does the re-arrangement of chemical bonds happens due to electromagnetic interactions?

The question is of some interest because the storage of energy in a recharable battery is not caused by gravitational (potential) nor by kinetic energy. From this question Why is current the same in ...
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### Switching Parity in a Superconductor

I've got a pretty simple question that's been bothering me for a while. This is the issue. Suppose we have a superconductor with phase $\phi$, and we change this to $\phi+2\pi$. One would think that ...