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Bicycle physics

From a long time, I have a question that bicycle is not stable at low speed or for that matter it's difficult to balance bicycle on its wheels in static position ( with zero speed and no brakes). Can ...
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1answer
16 views

How to find the initial speed on the y axis while only having Dy, Dx, angle, and acceleration

Is it possible to find the initial speed of a projectile on the y axis while only having $D_y$ (distance on the y axis), $D_x$ (distance on the x axis), the angle and $a_y$ (acceleration on the y axis)...
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0answers
5 views

electric field inside the surface with light is at normal incidence

I read that at normal incidence the polarizations of sigma and pi are indistinguishable so how can I find the electric field then if I cannot use either case's equations? Also if the light is from air ...
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17 views

Given acceleration, why must kinematics be used when solving for distance in terms of time rather than the literal definition of acceleration?

I'm working with rotational motion, and one of the mistakes that I made in solving for distance in terms of time was substituting angular acceleration for (d/Rt^2) where d is distance and R is the ...
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1answer
28 views

If space-time can be warped or curved, Doesn't that mean that It need space to be curved?

There is a doubt that i've always have and no one has given to me a satisfing or good response, i hope someone give me the response. Lets Talk about space only. If space can be curved or warped, that ...
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0answers
8 views

Extinction cross section and elastic forward scattering

It's often written that the extinction cross section ($\sigma_{\text{ext}}$) defined along a path of length $\ell$ is the sum of absorption ($\sigma_{\text{abs}}$) and scattering cross sections ($\...
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0answers
11 views

Commutator Angular momentum squared with position

I have to calculate this: $[\vec{L}^2, \vec{R}]$, I've got $([\vec{L}^2, \vec{R}])_i=[\vec{L}^2, X_i]=2\hbar^2X_i$. Is it correct?
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10 views

2D electron system: delta function impurity and principal value integral

This question refers primarily to this paper by R. Prange. The author considers a $2D$ electron system with a single impurity modeled as a $\delta$ function. The end goal is to show that when the ...
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1answer
35 views

Why can't we fly aeroplane or shuttle directly into the space (beyond 100 km height above Earth's surface)?

Without rockets can we go beyond Karmans line by shuttle or plane?
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0answers
11 views

Simple model for friction in a pivot joint

Consider a pendulum that is attached to its pivot point using a hinge or ball bearing joint. What is a simple but reasonable approximation for modelling friction in that joint? Background: I'm ...
1
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1answer
26 views

How magnetic monopole modifies faraday's law

I have encountered a statement that upon existence of magnetic monopoles, the equation $$\nabla \times \textbf{E} = -\partial_t \textbf{B}$$ must be modified. I only see that the last equation $$\...
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0answers
59 views

Why do we still call the electron charge the elementary (EM) charge?

The electron is an elementary particle, part of the SM, pointlike, with no substructure, or spatial extent. Its intrinsic properties include its EM charge, which we still call the elementary charge. ...
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25 views

What is the spinor representation of other groups beside $SO(p, q)$?

I am studying a lecture about superconformal algebras and it claims that there is a superconformal algebra in $d=5$ where supercharges belongs to spinor representation of $F_4$ (which is an ...
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0answers
16 views

The intensity of light coming from a distant star

The intensity of light coming from a distant star is measured using two identical instruments A and B, where A is placed in a satellite outside the Earth’s atmosphere,and B is placed on the Earth’s ...
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1answer
22 views

Is the capacitance of two isolated conducting spheres connected to each other by a wire equal to the sum of capacitances of each sphere on its own?

I have a homework problem, in which if I assume that the answer to the question in the title is True, then I get a right answer. I do not have good arguments why it is true though. How should I ...
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1answer
27 views

How to find the probability of a state from non-degenerate spectral decomposition

I have just begun learning the topics of time evolution in quantum mechanics, and I'm having trouble understanding how to calculate the probabilities of certain eigenvalues of an operator at a later ...
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1answer
39 views

Question about the Dirac adjoint and Feynman slash notation

I was trying to prove the identity $\overline{\displaystyle{\not}{a}\displaystyle{\not}{b}\dots \displaystyle{\not}{p}} = \displaystyle{\not}{p}\dots \displaystyle{\not}{b}\displaystyle{\not}{a}$. On ...
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1answer
30 views

Find the density of states of a bouncing ball

Imagine a ball falling from a maximum height of $h$ and colliding with the ground at $z=0$. The ball only moves in the z-axis and the collisions are elastic. My job is to show that the density of ...
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0answers
9 views

NMR Bloch equations in 4D?

I'd like to apologize for the purely theoretical question in advance, but I find this an interesting thought-excercise. So basically me and my coworkers asked how the Bloch-equation would look like "...
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0answers
22 views

D7-brane in Type IIB and axio-dilaton

In the context of Type IIB string theory with one D7-brane we have the following situation. The axio-dilaton complex scalar is defined by $\tau:= C_0+i e^{-\phi}$ where $C_0$ is the axion and $\phi$ ...
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0answers
11 views

Is it possible to equate the radius of a hole using poiseuille's law?

I want to calculate the radius of a hole from the leak rate. I have come across Poiseuille's law which includes the radius of pipe/hole. Is it possible to equate the radius of the hole from the volume ...
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1answer
36 views

What happens if water is prevented from freezing due to pressure; where does the energy go?

Say you have an iron (or whatever strong material) ball filled with water, and you leave it in a frozen environment (say $-100\ \mathrm{^\circ C}$); once it gets cold enough, the water will want to ...
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1answer
11 views

Does potential difference depend on the size of an object

Let's say object A has received a number x of electrons and is now at a 1v higher potential relative to a neutral ground. Now if object B which is 2 times bigger than object A receives the same ...
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0answers
26 views

Transformation between a dynamical system to a Hamiltonian system [duplicate]

Consider a dynamical system characterized by these equations $$\dot{x}=x-xy \\ \dot{y}=-y+xy$$ If we transform $\ln(y)=q$ and $\ln(x)=p$, the system can be changed into a Hamiltonian system with $q$ ...
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1answer
29 views

Electric potential and its signs

When we are calculating the potential due to the sphere, why do we integrate from $r$ to $\infty$ instead of from $\infty$ to $r$? Or do we integrate from $r$ to $\infty$? Regardless of who does the ...
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0answers
28 views

Non-linear sigma-models on curved worldsheet

I am studying nonlinear sigma-models and topological twists using E.Witten's article "Mirror manifolds and topological field theory" (https://arxiv.org/abs/hep-th/9112056), as well as "Mirror symmetry"...
4
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1answer
99 views

Phenomenon: dust in candle wax

I happened to encounter an interesting phenomenon in candle wax. As shown in the video, small dust near the fire seem to move back and forth, as if there is some kind of repulsive and attractive ...
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1answer
38 views

Kraus operators of a classical quantum channel

Consider a channel $\mathcal{E}: A\rightarrow B$ that maps quantum states $\rho_A\in A$ to $$\mathcal{E}(\rho_A) = \sum_i \langle i\vert \rho_A\vert i\rangle\tau_i\ ,\tag{1}$$ where $\tau_i\in B$ ...
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0answers
28 views

Why an ideal gas expands in the 2nd step of carnot's cycle/engine?

In the 2nd step of carnot's cycle, when the gas cylinder is kept under an adiabatic condition, it expands and the temperature falls. My question is why does the gas spend it's internal energy to ...
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0answers
17 views

Difference between Debye frequency and highest phonon frequency

In my lecture it says that the Debye frequency is the cutoff frequency. So is this also the highest phonon frequency? And if not, what is the difference? A little background: I do have an exercise ...
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0answers
13 views

Are there experiments specifically testing for electrostatic charge when light enters a medium?

I'm aware of the Faraday effect that occurs when light enters a medium, which suggests that there could be some interactions between magnetic fields and light: https://en.wikipedia.org/wiki/...
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19 views
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1answer
42 views

Rate of change of acceleration

I am trying to figure out some equations for a program I'm writing and I'm kinda stuck. I don't have the best experience with math or science so bear with me here please. I am trying to calculate ...
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0answers
42 views

Lagrangian Involving a Integral

This is my first post here, so do let me know if I am asking anything or in any manner unproperly! I am trying to construct a Lagrangian for a dynamic Euler-Bernoulli beam (with one end cramped) with ...
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1answer
30 views

Why the gravitational potential energy at infinity is zero?

If an object is taken from earth's surface to infinity, it's gravitational potential energy becomes zero (always taken as zero), but it doesn't make any sense as energy can never be destroyed so where ...
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0answers
12 views

Query concerning black holes [duplicate]

What information can be conveyed from a black hole about the substances and radiations it absorbs into it's singularity.
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7 views

How can we differentiate different parallel planes with the same Miller indices?

How can we distinguish different parallel planes with the same Miller indices not by graph and just with the numbers?
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35 views

Friction on Inclined Plane [on hold]

Please refer to the following picture: A mass m1 is placed on a ramp whose surface is frictionless. Another mass m2 is placed on top of m1. Release both masses so that they start sliding down the ...
1
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1answer
19 views

Potential of hydrogen atom solution of the Laplacian: Missing boundary condition to fix integration constant $c_1$

I have following problem, I want to calculate the classical potential $\phi(r)$ of the hydrogen atom in its ground state. The charge density is known: $$\rho(r)=\frac{-e_{0}}{\pi a^3}e^{-\frac{...
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0answers
11 views

Beam Deflections of a simply supported beam in terms of forces acting on the beam

I came across this formula for the bending moment of a simply supported cantilever beam with a point load added in the center: M=WL/4 I am currently investigating the effect of distance between the ...
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0answers
37 views

Conservation of energy in decay

A Λ0 particle of rest mass 1115.7 MeV and kinetic energy 172.6 MeV decays into proton of mass 938.8 MeV/c^2 and momentum 428.8 MeV/c and a "mystery" particle - calculate mass of mystery particle and ...
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1answer
58 views

Problem on conservation of energy

A parcel is launched at speed of $3.0\; \mathrm{ms}^{-1}$ up a rough plane inclined at an angle of $35^o$ above the horizontal. The coefficient of kinetic friction between the parcel and the plane ...
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0answers
10 views

Forces acting on a charged particle [on hold]

List down the forces that act on a charged particle when, a) it is at rest and b) it starts to move.
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0answers
35 views

How do we find a momentum space eigenfunction?

A particle moves in a 1D potential. The potential gives rise to a uniform force field $F$; $V(x)=-Fx$. The enegy $E$ is a horizontal line. How do we find a momentum space eigenfunction? $\dfrac{\...
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3answers
55 views

Newton's third law and Coulomb's law

Coulomb's law states that if we have two charges $q_{1}$ and $q_{2}$, then $q_{1}$ will act on $q_{2}$ with a force $$ \textbf{f}_{12}=\frac{q_{1}q_{2}}{r_{12}^2} { \hat {\textbf {r}}_{12}},$$ and $...
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3answers
188 views

Justification for excluding gravitational energy from the stress-energy tensor

I did general relativity years ago at Uni and was just revising with the aid of Dirac''s brilliant book; the beauty of this book is that it is so thin and concise. On reading this book I find that I ...
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2answers
50 views

Is there a connection between spontaneous symmetry breaking and massless photons?

I haven't studied a lot about these topics to put it that way. But I wonder if there is a connection between spontaneous symmetry breaking and the fact that photons are massless? The spontaneous ...
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0answers
24 views

Two particle Heisenberg model with field

I'm having trouble solving a problem with a phase transition of this system. We are considering the following Hamiltonian: $$H=-J \vec{S_1}\vec{S_2}-\mu b (S_{1z}+S_{2z})$$ And I've studied it in ...
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0answers
11 views

Is Coefficient of viscosity frame dependent? Why/Why not?

Is Coefficient of viscosity frame dependent? Why/Why not?
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0answers
37 views

The expected value of $x$

How to get the expected value of $x$ in the momentum space?

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