# All Questions

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### How quickly does the temperature rise in a water container submerged in a hot water bath?

Let's assume I have a small bottle (neglecting any insulation from the walls of the bottle) containing e.g. 150ml water at 4°C and place it in a larger pot with sufficient water at 80°C so that the ...
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### Simple derivation of the doppler limit and recoil limit

Im doing an essay on laser cooling, and I've got two questions about the derivation of the two limits. Firstly, in the derivation of the Doppler limit, it is stated in many places that the scattering ...
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### Conservation of momentum wrt center of mass

"A person with mass m is sitting on one end of a lifeboat of uniform density. Mass of lifeboat is 3m. The person then walks a distance of L to the other side of the lifeboat. Which of the following ...
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### Motion in vacuum

If we have a hollowed sphere in a vacuum, and its hallow space is filled with vacuum. In the center of the hollowed space inside the sphere is a ball. If we push the sphere does the ball move? (prior ...
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### Multiple Intersecting Universes

I am not a relativist or cosmologist, so this is very qualitative: I imagine a pair of universes, where each has two spatial dimensions (plus time), embedded in a 3-D (plus time) space, and these ...
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### How does one actually use the Einstein field equations?

I'm experimenting with the Einstein field equations (EFE) and I'm wondering how to actually use them. It seems to me that the simplest are those evolving a vacuum, which imply that the ...
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### Torsional spring and Euler angles

I have a question about the moments generated by torsional springs. Consider an inertial reference frame A and a body fixed reference frame B. The frames are connected by 3 rotational springs acting ...
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### Calculation of water bulk modulus using equation of state

I simply want to calculate the bulk modulus of water at 50C and increasing pressures. I think I am correctly calculating the new specific volume from the original conditions at (25C and 1atm) to 50C ...
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### Is it possible that a plane in turbulences has more downward acceleration than gravity's

In multiple Hollywood movies and TV shows I've seen scenes where a plane enters turbulences and for a moment the people in the plane seem to move upwards relative to the plane. As far as I know, as ...
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### Element 137 - Theoretical limit [duplicate]

I've seen a few sources that mention the speed of an electron in a hydrogen atom is 1/137 the speed of light. This article also mentions what looks like a correlation between atomic number and the ...
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### Water volume vs. pressure [on hold]

I have a pump that can deliver 14000 liter per hour. It is rated for a lift of 6m and a push of 36m. It has a 4m long 25mm hose as inlet(fed from a 30,0000l tank) and a 25mm outlet connected to 2m ...
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### Kinetic to Electric Energy

Not the best with understanding the formulas involved with the calculations but here is the gist: I want to use Faradays law to convert the kinetic energy from actions such as shaking to produce ...
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### Physical meaning of weight function in inner product in Quantum Mechanics

When taking the inner product of say two functions in Quantum Mechanics,we include a weight function w(x,y,z) that is usually equal to unity(in my undergraduate introductory QM course anyway). But ...
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### Pulling a bar through a magnetic field

This is a question on magnetic flux and induced voltage. I believe that this problem's answer key is incorrect, and I want to determine whether my opinion is sound. I also want to explore one ...
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### Why do some stars actually produce “Gamma ray bursts”?

I looked it up but I haven't found any explanation as to why some stars produce them, I understand that collapsing and merging stars produce them, but my question is why is the energy concentrated in ...
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### Feynman exercise - crystal lattice

Can you explain why there is no crystals with a shape of regular pentagon? (Usually wall of crystal have shape of triangles, squares or hexagons). Could it be a correct solution? Let's assume that ...
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### do Significant Figures apply with numbers without units?

say i need to divide a number with a unit to a number without a unit, e.g.: 16.4 meters / 2 Following the rules on significant figures, will the correct answer be 8.2m (since 2 has no unit), or 8 m ...
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### How is a vacuum able to propagate light?

We say that sound waves need a medium to propagate and we know that light doesn't need such a thing. But is that really how that works? There's no such thing as "nothing" according to Quantum ...
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### Half deflection in a galvanometer [on hold]

Why is half deflection taken while measuring the resistance of a galvanometer? Can't we take deflection in other ratios? Please help. I meant to ask while taking out the shunt resistance, why do we ...
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### Zero Field Magnetic Susceptibility of BiSCCO

I have been searching in the literature, with no results, for the (Zero Field) Magnetic Susceptibility of BiSCCO, but I cannot find any article regarding that. Does someone have a reference that ...
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### Michelson Morley experiment - why is there an interference pattern in the first place?

In descriptions of the experiment, the two arms of the interferometer have the same length. There's an interference pattern which was expected to be shifted when the system was rotated 90 degrees. But ...
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### Quantum field theory's interpretation of double slit experiment

After reading Art Hobson's article titled, "There are no particles, there are only fields" published in The American Journal of Physics in 2013, I'm wondering what other experts think of his main ...
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### What physics concepts support the observation of the book and paper falling together?

you place a sheet of paper on a book, it falls with it rather than being separated & slowed by air resistance. What physics concepts support the observation of the book and paper falling together? ...
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### The thermodynamics of heating water in a rigid container

When the pressure on the liquid surface is less than the vapor pressure of the liquid at a given temperature, the liquid will start to evaporate. This is common sense. The problem is more difficult ...
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### Temperature and magnetic properties of graphite arc [on hold]

I am making plasma balls inside a graphite slurry and injecting salt water into them. What is the temperature of the plasma ?
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### Assumptions in two balls falling experiment

A typical undergraduate physics class problem to demonstrate the effects of conservation of momentum is to have two balls of different mass falling one above the other (the largest mass below) to the ...