# All Questions

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### How do you work out the energy requirement for a submerged pump?

I was wondering if you were to place a pump in a submerged container and then were to open a hatch allowing water to flood the previously vacant cavity how much energy would be required to discharge ...
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### How to calculate the thermal resistance of a piece of metal

I have a 5mm*15mm*25mm piece of iron that I am going to use for an electrical connector. I calculated the resistance of it using this formula : $R=\rho\times\frac{L}{S}$ Iron resisitivity is ...
44 views

### Curvature of a particle move

I'm simulating a particle movement following a normal distribution. How this is done: My particle has a constant speed v and every step the particle move, I ...
134 views

### Reciprocal Lattice of a non-bravais lattice

Is a reciprocal lattice defined for non-Bravais lattices? I'm trying to work out one for HCP structure and not figuring it out.
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### Can I tune a magnetic field to conduct heat from a rotating object?

Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?
951 views

### I touched a tree that was touching an electric fence and got an electric shock. How is this possible if wood is an insulator?

I touched a tree that was touching an electric fence and got an electric shock. How was this possible if wood is an insulator? The tree wasn't wet either, and it was a pretty strong shock too.
135 views

### What is the entropy of the universe at the time of the Big Bang?

(I asked this question in Philosophy.SE; but I was advised to direct it here, despite it being in my opinion somewhat too speculative for physics.SE). High entropy generally means high disorder; and ...
16 views

### Spectral Decomposition for Complex Conserved Current

What is the spectral decomposition for the vacuum expectation value of a complex conserved current $J^\mu(x)$, $\langle T\{J^\mu(x),J^\nu(y)^\dagger\}\rangle$?
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### What is a good book/e-book on flight dynamics, guidance, and navigation? [on hold]

I was looking into buying a detailed theoretical foundation book on flight dynamics, particularly geared towards navigation. Is there any solid comprehensive material?
502 views

### Minimal vs. Non-minimal coupling

What is the difference between Minimal vs. Non-minimal coupling in General Relativity? A brief introduction to Minimal Coupling in General Relativity could be useful too.
161 views

### photon polarization, uncertainty in Energy

A beam of red light is sent along the $z$ axis through a polaroid filter that passes only $x$ polarized light. The beam is initially polarized at $30$°, and the total energy is $10$ Joules. Estimate ...
131 views

### If a car appears in horison and within 2 seconds passes you by, whats the speed it's doing?

While watching the first 4 seconds of driving at 745 km/h is ludicrous from any angle wondered If we knew the curvature of the Earth in a "flat" desert, what would be the speed of the car? ...
106 views

### The status of the BICEP2 'discovery' after Planck 2014

The tumultous period after the original announcement that the BICEP2 experiment had supposedly detected strong evidence of cosmological inflation in the form of B-mode polarization in the cosmic ...
26 views

### Rotational KE in double pendulum

Why the Rotational Kinetic Energy term for the point mass of Kinetic Energy for double pendulum is not included in Lagrangian equation? \begin{align} ...
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### Quantum Simple Harmonic Oscillator Interpretation

I am just wondering what does the SHO system from quantum mechanics actually physically represent? Is it just a SHO of a quantum particle, seems a little too obvious for quantum theory? I'm from a ...
201 views

### Force on a coil inside of a voice coil

as a homework exercise we were given the following question: Given the following voice coil: With depth = 20 mm Permanent magnets with B = 1.23 T, Ur = 1.1 The coils has 20 turns, I = 1 Ampere. a) ...
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### Action and Reaction - Time lag

Is there a time lag between action and reaction ? If there isn't such a time lag, the reaction force must cancel the applying force although they act on different bodies. My second question is that, ...
33 views

### Drag versus centripetal force

I'm trying to see how extensive a gaming engine's physics are. Consider a spinning disc with a box on it which is free to spin around a vertical pole connecting it to the disc. The pole is more ...
24 views

### Why is radiance measured normal to the beam?

Radiance is defined as: $L=\frac{d \Phi}{\mathop{d \omega} \mathop{d A} \mathop{\cos\theta}}.$ I’m wondering why there is a $\cos \theta$ factor in the denominator of the radiance ($\theta$ is the ...
54 views

### Is it acceptable to base a physical theory on a philosophical idea?

Are theories that are based on the philosophy acceptable in Physics? If the theory is based on the philosophy that obtained from laboratory experiments, can it be accepted?
33 views

### Boundary conditions of stream function

I have to do an problem about solving numerically the flow that goes under an airfoil. The airfoil has a flap deployed downwards and I need to solve the mesh that it's under the airfoil. I have drawn ...
34 views

### Polarized light

A light is made up of electric and magnetic fields oriented perpendicular to each other. Can polarization lead to the removal of any of the field completely?
118 views

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

I am an 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 ...
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### How to calculate scalar neutron flux

I am really confused about the difference between flux and scalar flux. I have a specific question: If we have a parallel neutron beam of strength $\phi_0$ given in neutrons/cm$^2$s, incident on a ...
23 views

### Antimatter traveling back in time and gravity [duplicate]

I've been reading on the construct of considering antimatter as matter traveling backward in time, which seems like an useful tool. There seems to be some discussion around this concept, if ...
2k views

### Why isn't length contraction permanent even though time dilation is?

It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that ...
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### The use of Artificial Intelligence in physics resarch

I have been reading about a machine that observed a double pendulum and created equations that both described its motion and associated conservation laws. The authors claims: We have developed a ...
3k views

### How far into space does one have to travel to see the entire face of earth?

Virgin Galactic will take passengers aboard SpaceShipTwo as high as 65 miles above the surface of the earth. But from this altitude, passengers will only be able to see a certain segment of the ...