# All Questions

139,848 questions
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### Does an information-theoretical approach proof the equivalence of total order and total chaos?

In the light of information-theory, are a state with maximum and minimum entropy the same? In the case of gas (maximum entropy), one needs very little words to describe a part of the system, which ...
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### How can a non-rotating black hole or singularity be created?

Every star or other massive body in the universe rotates, if only a little. If such a body collapses, its spin, any spin at all, and thus, angular momentum approach infinity as r approaches 0. Angular ...
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### Time after which the 3 particles will meet? [on hold]

Problem is from Classical Mechanics: I am a beginner in Physics trying to understand the solution to the given below problem. Problem Statement: 3 particles are placed at the vertices of an ...
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### Could black holes be driving the expansion? A different perspective than others that have asked [on hold]

Disclaimer: I'm not a phycisist. I'm a computer science major, going to an engineer school, that's taken the required physics with calc 1 and 2. This is just an interest. Please correct anything that'...
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### What does it mean that charged particles in orbits undergoing acceleration would emit electromagnetic radiation?

One of the drawbacks of Rutherford's atomic model was that electron would emit electromagnetic radiation as it is continuously changing direction and therefore undergoing acceleration, in what form ...
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### Dimensionally inconsistent!

This equation doesn't seem to be correct. Dimensionally inconsistent, in fact! How then, is it established? $$s_{t}=v_{0}+\frac{1}{2}a(2t-1)$$ (In case you don't know, this is the equation used to ...
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### Are there cases where $\nabla\cdot\iiint\frac{\mathbf{J}(\mathbf{x}')}{\left|\mathbf{x}-\mathbf{x'}\right|}\mathrm{d}V' \neq 0$?

In Jackson's Classical Electrodynamics, Section 5.4 (Vector Potential), the author seems to assume that because $\nabla\cdot\mathbf{J} = 0$, the following holds for the current density (where the ...
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### Using Kinematic Equations when acceleration is not constant due to drag force

If you drop a ball in a vat of oil with a mass of 50 g and it reaches terminal velocity of 0.032 m/s, how long would it take to reach 1/2 of terminal velocity? The drag force equals $F_d$ = Dv. I ...
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### Frictional force between ground and sphere [on hold]

In this question I was asked to draw the free body diagram of the sphere. In the free body diagram, there were two forces in horizontal direction (1) normal reaction from wall (2) horizontal ...
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### Force on Dielectric on pulling it out from capacitor

This is the text from Griffiths Electrodynamics for calculating force on dielectric on pulling it out from capacitor when the capacitor is connected to Battery so that voltage of capacitor is fixed: ...
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### Change of basis in the many worlds interpretation?

Say we have two orthogonal states $|A\rangle$ and $|B\rangle$. In the many worlds interpretation, we can imagine two parallel universes in which we are either in state $A$ or $B$. But now if we ...
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### Photoelectric effect confusion

I just have a quick confusion, so photoelectric effect says that light or photon act as particles not waves, however the photon energy is given by $E=hf$, so shouldn't the photon be initially a wave ...
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### Pressure required to form a black hole, explained to a ten year old

I could point to a mountain and say: gravity in a Black Hole is so strong, it would crush that mountain into the size of a grain of salt. But I am looking for something more concise, like the pressure ...
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### Prove that a transformation is canonical by using $\mathbb{M}^T\cdot \mathbb{J}\cdot \mathbb{M}$ [on hold]

So, I was given the following problem to solve: A system with two degrees of freedom is described by the following hamiltonian H=p_1^2+p_2^2+\frac{1}{2}(q_1-q_2)^2+\frac{1}{8}(...
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### Is there any graphs that demonstrate the Tsiolkovsky rocket equation? [on hold]

For example can you see the equation from analysis of a graph?
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### How much weight can we pick up with current tools? [on hold]

I'm curious about how much weight can we pick up with the tools have now. I tried to find it on the internet but no luck.
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### How to estimate the error in the positioning of an airplane if there was no relativistic correction? [on hold]

I need to resolve this exercise on relativity. The position of an airplane in flight is made by triangulation. Radio signals are emitted by the airplane at regular time intervals and picked up by at ...
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### Is there a superposition principle for the motion of interacting charges acted upon by external EM fields?

Consider a system of charges interacting with one another via their EM fields together with external EM fields applied to the system from outside. Suppose we work out the equations of motion ...
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### Photon creation operator physical realization

I am trying to self study QED so I apologize if my question seems silly. As I realize, all physical processes should stem from some "hermitian" operator in the quantum language. As it is well known, ...
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### What's wrong with my work? (calculate spring stiffness constant) [on hold]

So the prompt is as follows: A 1100 kg car moving on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.3 m. What ...
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### Convert emotion into energy? [on hold]

if it were possible to quantify emotion, would it be possible, theoretically, to then convert it into usable energy?
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### Are there more than 3 dynamical pictures of quantum mechanics?

There are 3 well known dynamical pictures of quantum mechanics: the Schrödinger picture, the Heisenberg picture and the interaction picture. In above wikipedia article, their connection is nicely ...
### What is the critical temperature for a BKT transition in the 2D quantum XY model with $S=1$ (not $S=1/2$)?
What is the critical temperature for a BKT transition in the 2D quantum XY model with $S=1$ (not $S=1/2$)? For instance, the classical XY model has KTc/J = 0.898 and the quantum XY model with S=1/2 ...