# All Questions

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### Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
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### Books on quantum mechanics with intuition [duplicate]

So, I know that there are a lot of questions about good books on quantum mechanics and I have read each one of them, and I go on and bought Griffiths' Introduction to Quantum Mechanics. But the fact ...
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### The significance of the pressure term within the momentum-energy tensor

Taking the momentum energy tensor T$_{\mu\nu}$, I am trying to understand the origin and significance of the pressure term p included within it. I am also confused as to where potential energy is ...
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### Molecules from atoms

Why does two oxygen atoms combine to form a molecule and not 3 or 4?Also why does one sodium and one chlorine atom combine to form NaCl while two chlorine atoms are required to combine with one ...
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It sounds like a joke but I just want to know if shadows have mass, since shadows are formed when there is blocking of light. It forms a black pattern with no energy therefore it has no mass.
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### Need help in understanding tensorial simplification in a special case

The Lagrangian of N=2 supergravity's important terms for my purpose are (hopefully I simplified this correctly): ...
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### Foci of elliptical path

I have read the Kepler's laws of motion where I came across the term foci of elliptical path. But what is really a focus? Can anyone please explain what is a focus (maybe with a diagram) and why a ...
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### Voltage and volume, same SI symbol, how to discern between the two? [on hold]

Both are SI quantities that use the same symbol, namely $V$. It annoys me that I might be working with the wrong unit even though it's easy to see if it's voltage or volume by looking to the whole ...
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### Initial current, RC Circuit

The task goes like this: The voltage between the points A and B, in the circuit diagram below, is 100 V. What's the initial current through the resistor when we close the switch S? (Other components - ...
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### Wavy stream of liquid

When pouring a liquid into a glass some streams have a wavy shape, like the one in the following photo: (Couldn't find a better picture, sorry.) What causes the stream to be of such a shape?
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### Finding displacement of spring

Q) A block lies on a horizontal frictionless surface, and the spring constant is 50 N/m. Initially, the spring is at its relaxed length and the block is stationary at position x=0. Then an applied ...
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### Why does water pouring from a glass sometimes travel down the side of the glass?

If you have a glass of water, say, three quarters full and you pour it at an angle of say, $45^{\circ}$ with respect to the the table, the water comes out of the glass and goes directly down towards ...
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### Why pouring milk from a height makes a chain shape?

I have noticed a chain-like shape when milk is poured from a height into a cup. Actually the chain pattern repeats itself after some distance and again till it reaches the milk in the cup. Any ...
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### Solving the Three-body problem numerically

I want to create a program in $Mathematica$ that solves numerically the Three-body problem by Euler-Lagrange's equations. I was searching some methods to sucessfully do it. So I found a way to solve ...
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### Why are nonrelativistic methods used in binary pulsar systems (gravitational waves)?

Although gravitational waves are a subject of the General Relativity, why do most books use Newtonian equations of motion for power radiated and rate of change of eccentricity calculations? In most ...
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### How often does a GPS receiver receive microwave signals from satellites?

I'm just finishing up a report on the mathematics of GPS, but I'm not sure how to determine how often a GPS receiver actually receives data from the satellites. If a satellite send out its microwave ...
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### Is it possible to blur an image in such way that a person with sight problems could see it sharp?

If someone has short or long sight, is it possible to tune image on a computer monitor in such way, that a person could see it sharp as if they were wearing glasses? If not, will 3d monitor make it ...
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### Atomic flux on the surface?

I have a surface which is made up of two triangles of unequal areas. I impinge a single atom on the surface at a certain angle at a certain time interval. As flux is atoms/unit area/unit time. In ...
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### Instant centre of rotation for two connected gears

The two gears are have the angular velocities $\omega_1$ and $\omega_2$ respectively with respect to $Oxyz$. The task is to determine the angular velocity $\boldsymbol{\omega}$ of the arm ...
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### Kerr Metric in Orthogonal form

I've seen the Kerr metric usually presented in the Boyer-Lindquist coordinates where there is a cross term in the $d\phi$ and $dt$ term. I've done a good bit of searching and cannot find any ...
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### air pressure in elevator

An elevator is accelerating upward. 1-How will the air pressure(P0) change? Will it decrease, increase or it doesn't change? WHY? 3- How will the formula of pressure(P=pgh+P0) change? 4- If a ...
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### Can someone give an intuitive understanding of Fano Resonance?

I'm reading about Fano Resonance. The line that almost every source I can find gives is something like (from the wiki): The Fano resonance line-shape is due to interference between two ...
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### Can dark matter be converted to dark energy?

According to energy mass conversion law, mass can be converted to energy. So is it possible to convert dark matter into dark energy?
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### Lagrangian Coordinates in Fluid Flow

I apologize if this is not the right place to ask this question: I am currently reading a paper by Y. Brenier, where for the fluid flow he introduces a Lagrangian label $a$ instead of the vertical ...
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### Quantum mechanics not in $L_2$-space [duplicate]

As far as I understand the postulates of quantum mechanics use only properties of abstract Hilbert space. So could we use any other Hilbert space for calculations instead of $L_2$? What could it be? ...
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### Magnetic field size from electric field

An electric charge oscillates about the origin along the y axis. A distant observer is located at a point on the +z axis. You observe the wave from a given location and find that at a given ...
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### Graphene plasmonics, Integro-differential eigenvalue equation

In my research around plasmonics in 2-Dimensional nanostructures like graphene, I encounter an eigenvalue integro-differential equation of the form: ...
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### Deriving the geodesic equation [closed]

I having been reading a general relativity book, but when in comes to the geodesic equation, it is not derived. How does one go about doing this?
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### How can I tell apart the composition of my soft ferrites

I have an assorted bunch of soft ferrites. I need to know which ones are MnZn and which ones are NiZn, so I can sort them for usage at different frequencies.
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### Two bricks glued together

If we have two identically shaped bricks of different mass, and we glue them together, and then drop them without air resistance, they will not rotate. However, if we look at the torque experienced by ...
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### Spinning Ball in Frictionless Tube

If we have a ball in a frictionless tube, and we begin to spin the tube about one end, the ball will exit the tube, correct? Indeed, there must be some centripetal acceleration, but then what force is ...
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### How do we “cancel out” the torque from running?

Running certainly causes a torque on our body, as we are propelled forward via our feet; why doesn't this torque cause our bodies to spin about their center of mass?
### Derivation of $v=u+at$
I read the derivation of $v=u+at$ using integration. The steps are as follows - $$\frac{dv}{dt}=a dt$$ $$dv=adt$$ $$\int dv=\int a dt$$ $$\int dv=a\int dt$$ $$v=at+c$$ My questions are as follows - ...