# All Questions

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### Increase thinking capability through relativity

As Einsteins relativity suggests that everything slows down along with the speed of light. So, if we were to live in space would our thinking capability (essentially speed) increase or decrease (due ...
0answers
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### Is $SO(10)$ GUT a complete particle theory (excluding gravity)?

Is $SO(10)$ GUT a complete particle theory (excluding gravity)? This particle theory seems to have a great preponderance of adherents. In fact, it is difficult not to run afoul of one or two of them ...
4answers
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### What is the current of a capacitor when the derivative of voltage is undefined?

This is from the textbook I am reading: I know this equation for capacitors: $$i=C\cdot \frac { dv }{ dt }$$ Here is my question: how can diagram (a) be allowed if the derivative of the voltage ...
2answers
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### Can two mediums have same refractive indices?

Can two mediums placed under same conditions* ever have same refractive indices? *Pressure, temperature,etc.
0answers
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### Why do floating objects attract?

Objects floating on the surface of calm water seem to be attracted to one another and tend to come together in a drift. Is this attraction like gravity?
0answers
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### Mutually unbiased bases

This question can be formulated in two ways. Let there be two $d$-dimensional orthonormal bases $B_{1}$ and $B_{2}$. I refer to the elements of $B_{1}$ by $\lvert\nu_{i}\rangle$ and to the elements of ...
0answers
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### Mirror Transportation

Why do people transport mirrors in inclined position? I frequently find people carrying mirrors in slant position on mini trucks.I guess it has some advantage of carrying them without breaking,and I ...
0answers
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### Occupation probability in grand canonical ensemble

I have a system with energy spectrum which has two groups of $N$ degenerate levels (the gap between them is $E$). There are $N$ non-interacting fermions in the system. What is the occupation factor at ...
0answers
22 views

### Ignition of thermal insulator [on hold]

A new type of insulating board has been developed by that esteemed construction company Kaput Ltd. They warn that at extremely high heat fluxes it could be ignited, but they don’t think it’s ...
0answers
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### Regional competition task from Physics [on hold]

I have attended regional competition in Physics today, and we have got following assignment: The underside of a smoky layer 7m x 10m is radiating like a flat, isotropic plate at 440°C to the floor ...
0answers
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### Applied / environmental question: direction of exhaust fumes

I'm not sure the Physics StackExchange is the perfect place for this environmental/applied physics question, but as I found no forum more fitting I ask my question here. Otherwise please move my ...
0answers
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0answers
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### Velocity in a pseudo-Riemannian manifold

Suppose we have a pseudo-Riemannian manifold (modeled by $\mathbb R^{p,q}$) with signature $$(\underbrace{+,+,\cdots,+}_p,\underbrace{-,-,\cdots,-}_q)$$ Meaning we have $q$ spacelike dimensions and ...
0answers
45 views

### How many equations are there to calculate distance?

I am a app developer and I am trying to build a physics app to calculate distance based on the quantities the user gives. for example if the user gives initial speed, time and acceleration, using ...
1answer
31 views

### Why is second moment of area often referred as moment of inertia?

In many references, mostly civil engineering, the second moment of area is referred as Moment of Inertia. Is that "really" correct? From my understanding, moment of inertia is analogous to mass in ...
0answers
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### What is the relationship between Elasticity and Compliance?

Compliance is like elasticity of hollow tube. Elasticity is greater for instance for arteries so they are less compliant. There seems to some short of inverse relationship. One figure about ...
1answer
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### Simple question about the tidal force (Leibniz's notation confuses me)

I started going through Taylor and Wheeler's Spacetime physics (standard textbook on special relativity). This is from exercise 2.8. Basically we're dropping a bearing ball from a 315 m height above ...
1answer
23 views

### Density as a function of Temperature?

I know that volume = mass/density....and density is the function of temperature. Is there any standard equation that describes density as a function of temperature? The system I am interested in is ...
0answers
48 views

### Monte Carlo estimation of Pi with Buffon's needle [migrated]

Is there a way of estimating Pi with the Buffon's method without assuming Pi known? To be more precise: in a Monte Carlo simulation of the experiment invented by Buffon I would (ideally) generate 2 ...
0answers
25 views

### Solutions of PDEs in different coordinate systems

Suppose we have a PDE, for example the Helmholtz paraxial equation: $$\nabla_\perp^2A+2ik\frac{\partial A}{\partial z}=0$$ Solutions depend on the coordinate system we are using, i.e. we obtain ...
1answer
42 views

### Writing an arbitrary operator in bra-ket notation

An annoying fact about my physics textbook (Griffiths' Introduction to Quantum Mechanics) is that it introduces bra-ket notation without telling us how to use it. So I have a two-part question for SE: ...
0answers
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### Calculate measured energy of particle in moving observer's frame [on hold]

A particle with rest mass $m$ and 4-momentum $p^\mu$ is examined by an observer with 4-velocity $\eta^\mu$. To simplify some formulas, in this exercise we use units in which c = 1. Show that: ...
0answers
31 views

### How to deduce equations 3.6.15 in Polchinski's string theory book? [duplicate]

In polchinski's first course on string, with how to deduce
1answer
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### Refrigerator cooling power usage

I have a refrigerator, that makes a lot of noise, and we have therefore set a time on it will limit the run time to when we are not at the office. But this is where our discussion begins, should we ...
1answer
31 views

### Microcanonical Ensemble

I'm having difficulty understanding a statistical mechanics problem. I'm missing some basic understanding of counting the minimum energy states. My thought is that there are three states to choose ...
1answer
482 views

### Why quantising gravity necessarily give us gravitons?

Gravitons are supposed to be the quanta of gravitational field My question is, if we do not know how to quantize gravity yet, how do we know that quantizing it in principle should give us gravitons, ...
2answers
42 views

### Calculate height of object from $v=u+gt$ [on hold]

"Ms. Woods returns a hard disk drive to your shop claiming that it needs to be replaced, due to an unknown hardware malfunction. A diagnostic test of the drive reveals that the 'fall detection' system ...
2answers
52 views

### Quarks are now considered to be fundamentals, but so were atoms some time ago. So the way we see is only limited by our technological advances?

After watching this FuseSchool - Global Education episode, I cannot stop thinking how can something not have a substructure, how it cannot be split? http://www.youtube.com/watch?v=nlv06lSAC7c
1answer
30 views

### Airfoil theory — Why does air travel faster above? [duplicate]

I do not understand, why the air above the airfoil travels faster than the air below it? The air above has to travel faster than the air below so that both streams meet simultaneously at the ...
0answers
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### Stress energy tensor and the covariant derivative of the 4-momentum

Another basic question. I have usually seen the stress energy tensor $T^{ij}$ described as the flow of the 4-momentum field $p^i$ along direction $x^j$ in spacetime with $p^0$ as energy and $x^0$ as ...

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