All Questions

341 views

What is wrong with this downforce calculcation?

I tried calculating the downforce of a spoiler I need for a robot. I used this formula. $$F = \frac{1}{2}Ac_a\rho v^2$$ Where $\rho$ is air density, $v$ is the speed of my robot, $c_a$ is the lift ...
643 views

What generates such a huge amount of gravitational attraction in a black hole?

I had been fascinated to hear that anything can be swallowed by a black hole. But what causes such a huge amount of gravitational force?
3k views

Finite potential well problem - calculating the ground state

1. The problem statement, all variables and given/known data Electron of is in a 1-D potential well of depth $20eV$ width $d=0.2 nm$ in his ground state $N=1$. What is the energy of the ground ...
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What do you call the period after sunrise when the sky is bright?

At sunrise, the sky isn't actually up in the sky yet. Twilight occurs before sunrise, then at sunrise the leading part of the sun crosses the horizon. But, the sky isn't bright yet. It takes some time ...
179 views

Measuring a quantity using two measuring devices

I would like to ask how I can reduce uncertainty by designing an experiment. I need to measure a quantity( say speed, in m/s). I have to calibrate the device and then move the device to measure ...
1k views

Projectile Motion Question involving a ball and a ramp inclined at an angle

The question is to finde the initial horizontal velocity of the ball at end of the ramp, where it is released. I know how to do this using gravitational potential energy and kinetic energy ...
147 views

Colors of light

White light is always said to contain all the different wavelengths of light. Why, then, can we 'make' new colors simply by adding wavelengths? Is it just a matter of our perception, that, when two ...
1k views

Born's Rule, What is the Reason? [duplicate]

As far as I've read online, there isn't a good explanation for the Born Rule. Is this the case? Why does taking the square of the wave function give you the Probability? Naturally it removes negatives ...
235 views

Wave packets Group Velocity

For the the group velocity of a wave packet, the group velocity is the partial derivative of omega with respect to the wavenumber, what does this mean? I thought that for some given wave packet both ...
4k views

Physical difference between Lorenz and Coulomb gauge-fixing conditions

Lorenz and Coulomb gauge-fixing conditions. What is physical difference between these two gauge-fixing conditions? Mathematical expression are clear but how to we choose one of these means what they ...
415 views

How to introduce the electromagnetic field in Quantum Field Theory?

There are many ways to introduce the electromagnrtic field in Quantum Field Theory(QFT), such as canonical quantization method which introduces the creation and annihilation oprators by treating the ...
894 views

Church-Turing hypothesis as a fundamental law of physics

The Church-Turing hypothesis says one can not build a computing device which has more computing power (in terms of computability) than the abstract model of Turing machine. So, there is something in ...
137 views

Red shift and the expanding universe

Given that the universe is expanding because space itself is expanding, is that expansion occuring in all places and on all scales? Consider a photon emitted from a source billions of years ago. As it ...
336 views

Fundamental Higgs vs. pseudo-Nambu-Goldstone boson: experimental fingerprints

If we consider the 126 Higgs-like boson as a pseudo-Nambu-Goldstone boson, what are the experimental fingerprints of that case? What are the main differences, in a purely effective field theory ...
155 views

$d=\frac{1}{2}at^2$ not giving expected results

Say I have an object that starts falling from rest at 2 m/s2. Its total displacement and velocity at the end of every second should look something like this: ...
249 views

How to superpose an wavefunction for an infinite potential well / interval - $-d/2 <x<d/2$

I know that two functions which describe the state of a particle in an infinite square (on interval $-d/2<x<d/2$) well are like: \begin{align} \psi_{even}&= ...
88 views

what is the radial extent of the last scattering “shell”?

At CMB recombination (z=1090), what is the radial extent of the last scattering "shell"? a) Delta(z) = .... b) Delta(comoving angular distance)= ....Mpc The WMAP first-year parameters give Delta(z) ...
312 views

On the atomic level, how is incandescent light structured?

I want to know from the smallest possible originating structures how the light I see generated from heat is made by atoms themselves.
280 views

Good place/supervisor for PhD in Theory of Condensed matter [closed]

I am currently finishing my undegraduate degree in physics and would like to do PhD in Theory of Condensed Matter field. Could you give advice on which are good groups/supervisors in the field. ...
161 views

What's going on along the “sides” of an Alcubierre warp bubble?

The models/depictions I've seen of warp bubbles show space compressed ahead of the bubble and expanded behind, so that the space inside the bubble moves with respect to the space outside. If that is ...
281 views

General Relativity and the effect of mass on time [duplicate]

My question is related to the first page of this article regarding the big bang theory and refers to this specific sentence: Armed with the best physics of the 20th century, Albert Einstein came ...
103 views

Interaction of external light or matter and an Alcubierre warp bubble

For a hypothetical vehicle traveling in an Alcubierre bubble at faster-than-light (FTL) velocities, what would happen when the leading edge of the bubble encounters incident particles or photons? ...
182 views

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Nuclear Fission and Fusion [duplicate]

I've read several other answers on here, but I still don't understand. Why do both fission and fusion release energy? I know the masses drop, but then why do the masses drop on both? Fusion is taking ...
438 views

Why is the Higgs boson created so infrequently at the CERN collider?

Although each collision at CERN has the available energy to create a Higgs boson each time, the vast majority of the time it does not create one. I suspect that part of the reason for this is that ...
794 views

Is everything made of massless particles?

Photons have no mass. Yet they interact gravitationally, as all energy does, with other energetic and massive particles. This means that if you put multiple photons in a system, you get something that ...
842 views

Conservation of Angular Momentum, as related to a flywheel

Trying to work out some pesky flywheel dynamics for a project I'm working on, would love some for your assistance to better understand the underlying concepts. For a given flywheel (thin-walled ...
111 views

Is a “supercritical charge” in graphene similar to Hawking Radiation?

These papers describe a phenomenon referred to as "atomic collapse" and "supercritical charge" in graphene: Wang et al., Pereira et al. "Atomic collapse" appears when you have a large enough Coulomb ...
618 views

Law of conservation of energy and kinetic energy: deformation of a spring [closed]

Problem: A block B of 1,5 kg is attached to the right of a spring (not deformed, with its right side attach to a wall) with a constant of $k = 80 N/m$ and, at rest, the block enter in collision with ...