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I am a student and due to school closures I am reading ahead in physics. I have been learning about relativity and I made up a problem for myself. You can see a diagram that I drew below:
The diagram shows car X travelling at $0.7c$ with respect to car B and $0.5c$ with respect to car A. Car A is travelling at $0.2c $... |
I am trying to read Fradkin's book "Field Theories of Condensed Matter Physics" but I am finding it to be a bit hard to follow at some places. In particular, I find that Fradkin sometimes throws some formulas out of nowhere and while I can work through most of them, some are too difficult for me to understand/derive. I... |
I'm trying the derive the period of a simple pendulum using energy conservation and without calculus.
I'm doing something wrong which I can't figure out.
I see a lot of other derivations online using calculus which I want to avoid for now.
The pendulum has a length $L$ and is displaced by $\theta$ from the vertical.
Co... |
My understanding is that the intrinsic carrier concentration of a wide bandgap material tends to be lower than that of a narrow bandgap material.
$$ n_i = \left(N_cN_v\right)^{1/2}e^{\left(\frac{-E_g}{2kT}\right)} $$
and the open circuit voltage of a solar cell is
$$ V_{OC} = \frac{kT}{e}ln\left(\frac{J_{SC}}{J_o}\righ... |
Suppose I have a plane wave with wavevector $\mathbf{k}$ and polarization $\mathbf{\hat{e}}$. Is there a convention or some logical way of defining the polarization given the wavevector? I know that the polarization vector must be perpendicular to the wavevector, so the only free parameter to specify is the angle of ro... |
A cord is wrapped around the rim of a solid cylinder of radius $0.25$ m, and a constant force of $40$ N is exerted on the cord shown, as shown in the following figure. The cylinder is mounted on frictionless bearings, and its moment of inertia is $6.0 \mathrm{~kg⋅m}^2$. (a) Use the work energy theorem to calculate the... |
In Henneaux's Lectures on the Antifield BRST Formalism for Gauge Theories, it is claimed in Exercise 1 that diffeomorphisms $\delta_\xi A_\mu=\xi^\rho\partial_\rho A_\mu+\partial_\mu\xi^\rho A_\rho$ differ from ordinary gauge transformations $\delta_\Lambda A_\mu=\partial_\mu\Lambda$ by a trivial gauge transformation $... |
This is the delayed-choice quantum-eraser experiment of Kim diagram described on Wikipedia https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser
Why do I need a lens in front of the D0? Why we should focus photons? The classic Double-slit experiment does not require a lens.
What pattern will we see on D0 if we r... |
How are the two approaches of understanding gravity, the so-called 'Emergent/entropic gravity' and 'Quantum gravity' (String theory, LQG etc) differ from each other? I am very curious and will appreciate if somebody can sketch a summary.
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This is a sort of a generalized question and not just referring to the flow of current. This includes fluids and many other such entities.
But why does this flow occur. For example if I consider current, then the definition of potential at any point is the work done by external agent in bringing a unit positive charge ... |
One can show that for the phase difference $\Delta$ between the two wave functions (slit 1 and slit 2) it holds the first equality on the LHS
$$\Delta=\oint_{\partial\Omega} \vec{A}\overset{!}{=}\int_\Omega \nabla\times \vec{A}=\int_\Omega \vec{B}=\Phi_m$$
This is then used to proof a physically important result, namel... |
The Quantum Harmonic Oscillator in the ground state is specified by the following Gaussian PDF in two dimensions:
$$p(x,y)= \frac{M \omega_x}{\pi h}\sqrt{ \frac{\omega_y}{\omega_x}} e^{-\frac{M}{h}(\omega_xx^2+\omega_yy^2)}$$
where M = mass of particle, h = plank's constant, $\omega_x=\frac{h}{2M\sigma_x^2}$ and $\ome... |
Using the grand canonical ensemble, we can show that the occupation factor of an energy level (when the temperature $T$ and chemical potential $\mu$ are fixed) is given by $$ f_E(T,\mu) = \frac{1}{\exp \frac{E-\mu}{kT} \pm 1} \quad (1)$$. The total number of particles and energy in the system are thus given by
$$ N(... |
A system which is in a macro state may be in any of a large no. of microstates at a particular instant of time. But we see an average behaviour of the system. I don't understand why it is so ? Why don't we see the instantaneous state of the system ?
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What was the need to introduce the concept of S matrix in scattering theory?while we were studying scattering with partial wave analysis.
|
Let's say I've got a massless rod, at the end of which, I've attached 2 identical balls. Now say I drop the rod, such that it collides with the ground and for some reason, the coefficient of restitution of both the balls in their collision with the ground is different. In this case, the linear velocity would be differe... |
Is it necessary that a capacitor storage charge? I am a little bit confused.
For example: if I take two concentric conducting shells and a positive point charge at the centre. Both the surfaces (outer surface of the the smaller shell and the inner surface of the larger shell) are equipotential and have zero net charge ... |
A question I encountered is whether a pendulum undergoing SHM on earth will oscillate on the ISS. Apparently the answer is it won't due to no effective gravity. The argument is there will be no tension force as all of it is on free fall. How is this different to on earth, where the entire setup is acted upon by g.
|
From this link Heisenberg uncertainty principle,
It says:
Clearly, when $\Delta p_x$ shrinks, $\Delta x$ has to grow larger and larger in order to satisfy the Heisenberg inequality. For example, a plane wave $\psi(x) = \exp[2\pi i px/h]$ is an eigenfunction of $p = -ih/(2\pi)\ d/dx$, so that $\Delta p_x = 0$; a plane ... |
The picture on the right is what happens in real life but, I cant understand why electrons or negative charge carriers have to take this circuitous path to get to the positive charge, If the positive ions are pulling the electrons then shouldn't the positive and negative ions be adhering to the wall separating them wi... |
Is there a way to calculate the time it has to be on Earth at any moment in time when a person on the Moon would say their clock reads noon (i.e. a time at which a sundial on the Moon would cast no shadow)?
I would guess it has to do with the relative angle between the planes in which the Moon orbits the Earth and the ... |
I have two bodies of known mass $m_0$ and $m_1$. $m_0$ is at constant velocity of $v_0$ on a level friction-less plane surface, and $m_1$ is moving across the same plane at constant velocity $v_1$ towards $m_0$; the assumption is that $v_1$ > $v_0$ so they will collide at some point.
When the two bodies perfectly colli... |
I'm just wondering what's the difference between symmetry breaking and anomaly.
From my understanding, symmetry breaking means: there is a symmetry in the action, but in the ground state of the theory(minimum of the action), the symmetry becomes smaller, which is a subgroup of the original symmetry.
While anomaly means... |
I have interaction hamiltonian as
$${\cal H}_I = -\frac{1}{2}\sum\limits_{k\neq k',q}\sum\limits_{\sigma,\sigma'}\frac{\omega_{k-k'}M_{k-k'}^2}{\omega_{k-k'}^2-(\epsilon_k-\epsilon_{k'})^2}\hat c_{k'\sigma'}^\dagger\hat c_{-k'+q,\sigma}^\dagger\hat c_{-k+q,\sigma}\hat c_{k\sigma'}$$
and total hamiltonian is
$${\cal H} ... |
I am a student and due to school closures, I am reading ahead in physics. I have been learning about special relativity and I made up a problem for myself. I've drawn a diagram below:
The diagram shows Mr Green travelling at $0.5c$ in the $x$-direction with respect to me at the origin and Mr Red is travelling at $0.5... |
Rotations are part of the symmetries of nature
I heard that electrons carry a spin 1/2
Q: How do rotations acts on the spin of an electron?
The state of my reflection: irreducible representations of rotations are dimension odd. But the spin is dimension 2, so it is either invariant under rotation, either incomplete (... |
When reading Light Sterile Neutrinos: A White Paper I came around the following statement:
"A further difficulty in interpreting experimental evidence in support of a light sterile neutrino is that the effects are purely in count rates. The energy and distance-dependent
characteristic of the oscillation phenomena assoc... |
Suppose we have an ideal spring. We push the spring with our hand in the $x$ direction (so we don't need to take account gravity) exerting a force $-F_{h}$. From Newton's third law the spring exert to our hand a force $F_h$. Also the spring at some point where it is extended it will exert a force according to Hooke's ... |
If I have an arbitrary function of $n$ 4-vectors $f = f(q_1^\mu, q_2^\mu, ..., q_n^\mu)$ where $q_i^\mu$ are 4-vectors, what is the least number of Lorentz scalars I would need if I needed to specify the function's argument in the form $f = f(s_1, s_2, ..., s_k)$ where $s_i$ are Lorentz scalars? These k scalars could t... |
Its a question about entangled pairs and double slit experiment. I have seen and read many such on the stackexchange but I can not really understand what is happening! So please don't stop the question as a duplicate.
I would like to get an answer about an extremely simple scheme which is close to that of Birgit Dopf... |
There is a classical problem which is a bead in a vertical hoop that is rotating around its vertical axis. If $R$ is the radius of the hoop, $m$ the mass of the bead, $\omega$ the angular velocity of the hoop and $\theta$ the angle that represents the position of the bead measured from the bottom, the lagrangian is $$L... |
I am trying to derive the free-streaming length for the HDM particles but I couldnt follow the arguments given by the article https://arxiv.org/pdf/astro-ph/0201405v1.pdf after equation 83.
Thanks
|
I am trying to wrap my head around periodic potentials and weak periodic potentials from the reduced zone schemes. From the definition of $\psi_k$:
$$
\psi_k(x)=\sum_G C_{k-G}e^{i(k-G)x}
$$
I understand how $\psi_k=\psi_{k+ng}$ when $g$ is the smallest reciprocal lattice vector. As the sum is infinite a simple relabeli... |
I'd like to consider the 1D-oscillator phase space probability density evolution problem with the ordinary
Hamiltonian
$$H = \frac{p^2}{2m} + \frac{kq^2}{2}.$$
Then the Liouville theorem is just
$$\frac{{\partial \rho }}{{\partial t}} = { {\frac{{\partial \rho }}{{\partial {q}}}\frac{{\partial H}}{{\partial {p}}} - ... |
Suppose I have a linear homogeneous isotropic magnetic material, such that
$$\textbf{M} = \chi \textbf{H}\tag{1},$$ where $\chi$ is the magnetic susceptibility, $\textbf{M}$ the magnetization, and $\textbf{H}$ is the magnetic field.
In some articles/webpages, for exemple [1], [2] and [3], equation $(1)$ says how the m... |
I would like to get some information on the operational safety of this equipment. How much, approximately (just the order of magnitude) does the school Crookes tube with the Maltese cross, used to demonstrate cathode rays, produce X rays at 5-10kV DC (1–10mA) during, say, 10-15 seconds of work from a 1 meter distance? ... |
Reading up on how lasers work, I found out that there are lots of different materials that can be used as laser medium, from noble gas ions and halogens to metal atoms to organic dyes. So far I have understood that to get laser action your laser medium needs to have several energy levels, with a high level that is meta... |
I am grateful for any help offered:
Ignoring friction (and hence rolling), what are the forces in play on the ball in the middle frame??
I am attempting to mirror this diagram to make a half hexagonal shape. With this I should be able to visualise what would happen when the slope becomes more and more curved until it ... |
I was look around stack exchange and couldn't find a good answer to this: What is the relation of the band theory of solids and the X-ray diffraction? We know that it EM wave is scattered (the process is difraction from reflection [diffraction grating]) only if there is a vector in reciprocal lattice such that $\Delta ... |
According to the original paper of Glauber and Cahill
Ordered Expansions in Boson Amplitude Operators. K. E. Cahill and R. J. Glauber. Phys. Rev. 177 no. 5, 1857-1881 (1969).
the displacement operator's matrix elements with respect to the number-basis read:
$$
⟨m|D(\alpha)|n⟩=\sqrt{\frac{n!}{m!}}\cdot\alpha^{m-n}\cd... |
Reviewing the anomalies of the standard model, one knows that the Baryon number is not conserved because of an anomaly associated to the global $U(1)$ symmetry that quarks have. That is the current
$$J_B^\mu = \sum_\alpha \bar{\psi}_\alpha\gamma^\mu\psi_\alpha,$$
where $\alpha$ runs over flavors and colors, is not con... |
According to Wikipedia visible light lie between 405-790 THz https://en.wikipedia.org/wiki/Visible_spectrum
Can I just sum "maximum" spectrum of the light if by definition white light is sum of colors (frequencies)?
Like 405+790?
I just want to know what is frequency of bombarding by photons "white" noise rather specif... |
I just have a question on the terminology since I am a beginner and am not sure of it. If we have a $3$-qubit system
$$(a_1|0\rangle+a_2|1\rangle)\otimes(a_3|0\rangle+a_4|1\rangle)\otimes(a_5|0\rangle+a+6|1\rangle)$$
and then we multiply them together it will be:
$$a_1a_3a_5|000\rangle+a_1a_3a_6|001\rangle+a_1a_4a_6|01... |
I'm trying to understand CPT symmetries in the Dirac Lagrangian but, so far, I've had more questions than answers. My naive view of CPT transformations is the following (please don't doubt to correct me):
After a parity transformation, a spinor $\psi$ is transformed into $\psi'$ with $\,\psi'(x,t)=\gamma^0\psi(-x,t)$.... |
As we know, in an infinite square well, the energy is quantised and is given by $$E_n=\frac{n^2h^2}{8mL^2}$$
Now, suppose that there is an electron in the fourth excited state. Now, let us suppose that the electron starts going down to lower energy levels, thereby emitting photons in the process.
My question is-
Is it ... |
In this website, it was written that
If a force acting on an object is a function of position only, it is said to be a conservative force.
Why is this so? According to wikipedia, a force is conservative if it meets any of the following conditions:
$\nabla \times \vec{F}=0$
$\vec{F} = -\nabla V(\vec{r})$
$W = \oint ... |
Mermin-Wagner theorem says that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions $d ≤ 2$. (this is directly copied from wiki).
I'm just wondering that, if we could add some interaction, like Dzyaloshinskii-Moriya (DM) interact... |
When one looks up elementary particles on Wikipedia, as one of their properties their parity is stated. For example the Proton has parity $+1$, while a Pion has parity $-1$. I understand that you have to define the parity of some particles to have a reference to measure the parity of all particles (since one could jus... |
I want to ask a general question about two vast topics of applied electromagnetics: Guided and unguided (radiated) waves.
I have noticed that there are almost always some common strategies for dealing with such problems.
For the guided waves (for example, the eigenmodes inside a waveguide), we usually write the (Helmh... |
In the following video (not necessary to watch)...
https://www.youtube.com/watch?v=K_vWYEjgVRg&list=PLdnqjKaksr8pXF2SpDyyD7ouAVlz96_Ra&index=23
...the creator takes the projection of the phasor onto the $y$ axis to be the instantaneous value of the signal. I've seen a couple other lecture-notes online where the writers... |
The effective mass is defined as
$$
\frac{1}{m_{ij}^*} = \frac{1}{\hbar^2} \frac{\partial^2\epsilon}{\partial k_i \partial k_j}
$$
where, $m_{ij}^*$ is the effective mass, $\hbar$ is the Planck's constant, $\epsilon$ is the energy and $k_i,\ k_j$ are reciprocal latttice vectors.
Now let us consider that we have the val... |
I've been recently been assigned this exercise:
Consider two spin 1/2 particles which are coupled through a time dependent interaction:
$$ H(t) = a(t) s_1 \cdot s_2 $$
where $a(t)$ is a function which is constant in the interval $[0,T]$ and zero elsewhere.
The system is in the state $|+,->$ for $t \to -\infty$.
... |
I have seen that Gauss law works mainly because $\vec{\nabla} \times \vec{E}=0$, and that we are implicitly using this when finding the charge enclosed using Gauss law. Why is that? I have seen the derivation, and it solely uses Coulomb law. Is it because the Coulomb law describes an irrotational field and it wouldn't ... |
While deriving the Conservation of Energy equation for Fluids using First Law of Thermodynamics in a Lagrangian Co-ordinate, there comes a point where the Work done by Surface forces are converted to volume integrals using Gauss' Theorem. The author mentions it as a step to exploit arbitrariness of volume V considered.... |
Is it necessary that a capacitor stores charge? The definition of capacitor given in books is that it store electric energy. So is it possible that the capacitor does not store charge but stores energy only?
|
Hello Stackexchange physics,
This question is mostly a request for a source of information on quantum measurement and decoherence that is consistent and independent of the particular context.
When I read about quantum information in the context of quantum computers and play with the IBMQ, it appears I can get my entang... |
When a body travels at a very high speed, as far as its concerned, everything is in motion except itself, so according to the body everything around it looses length in the direction of motion and gains mass. Keeping these two facts in mind, should it not be possible to travel so close to the speed of light, that due t... |
Beginner to QFT - While Taylor expanding the exponential term of the S-matrix, why is the 2nd order term (quadratic time integration term) written with two different dummy variables for time? (Lectures on Quantum Field Theory by Ashok Das, page 231)
|
In Wolfgang Demtröder (auth.) - Atoms, Molecules and Photons we have this laser spectroscopic setup.
Without any explanation he claims the chopper can fix the Doppler broadening background shown on this graph here:
(a) Doppler-broadened overlapping absorption profiles with small Lamb dips.
(b) Elimination of the Dopp... |
I'm creating an asteroids game. For player movement, I want the spaceship to be slowed down as if by a drag force, see e.g. https://en.wikipedia.org/wiki/Drag_(physics), and only the drag force. The magnitude of the drag force is proportional to $v^2$, and I decree that all other parameters are constant in the fantasy ... |
If a massive body is moving at near light speed (or, hypothetically at light speed) and on course to hit Earth, will we feel its gravitational pull before it collides with us?
I think the answer is no because speed of gravity is same to speed of light.
Does it mean bodies moving at near light speed don't produce gravit... |
Consider the following question.
The answer is $C$.
I am wondering why is there no centripetal force at point R acting towards the center to give it a centripetal acceleration such that the resultant acceleration vector is pointing down and to the left (or southwest) when both gravity and the centripetal force are acc... |
I expect there is change as energy converts into matter and matter converts into energy. Is there an overall curve we have seen through observation that a galaxy goes through in its lifecycle or does it stay relatively flat?
|
I'm reading Isham's Lecture on Quantum Theory, and towards the end of Chapter 6, in Section 6.4.4, The Time Development of a Mixed State, he shows (not defines) that $\hat{P}_{|\psi_t\rangle}:=|\psi_t\rangle\langle\psi_t|$ evolves as $$\hat{P}_{|\psi_t\rangle}=\hat{U}(t, t_1)\hat{P}_{|\psi_{t_1}\rangle}\hat{U}(t_1, t),... |
How do you make a $(v,t)$ diagram with braking and deceleration?
When someone for instance brakes and then stops with an uniform acceleration?
|
From what I have read, the evolution of a quantum state is determined by the Hamiltonian (Schrodinger equation). However, I'm trying to understand if the Hamiltonian itself can be fully derived from the quantum state, or if it needs to be defined externally. From my understanding, the Hamiltonian includes information a... |
Apparently nice duality between classical and quantum mechanics first noticed by Dirac. As a graduate student of mathematics I believe such a wonderful similarity in their mathematics have a deep root and of course is not accidental. But I'm not so expert in physics that I could find and explain this root.
I also add... |
Let's fix a coordinates system $(x,y,z)$ with origin $O$. Considering a (screw or edge) dislocation and let the coordinate system $(x',y',z')$ with origin $O'$ move with the dislocation, and impose the condition that the two origins $O$ and $O'$ coincide at $t=0$. Then the following transformation holds
\begin{array}{l... |
I'm trying to understand how the idea of an infinite universe with presumably infinite matter works with the Big Bang and inflation.
I understand that if the universe is infinite, then it's always been infinite, and that when we talk about the initial universe being very very small, dense and hot we are referring to th... |
Today I came across a paper, "Experiments testing macroscopic quantum superpositions must be slow," by Mari et al., which proposes and analyzes a thought experiment involving a first mass mA placed in a position superposition in Alice’s lab, the mass mA producing a gravitational field that potentially affects a test ma... |
First of all, I will use a conclusion given by gravitomagnetism, but the example will concern Kerr black holes, and therefore lies in the realm of strong gravitational fields.
Well, gravitomagnetism gives us two Maxwell's equations analogs $[1]$,
$$\vec{\nabla} \cdot \vec{B}_{g} = 0 \tag{1}$$
$$\vec{\nabla} \times \vec... |
I'm trying to understand the exact mathematics of Lorentz invariance and I have a question. I hope this is a good place to ask.
To prove that $J^\mu dt=\rho dx^\mu$ defines a $4$-vector, my book says that for a small charged particle occupying the volumes $dV$ with charge density $\rho$ in a certain referential $R$, th... |
Could white holes undergo reverse hawking radiation? This is because of quantum mechanical uncertainty. So for example a pair of particles one a positive and one a negative energy particle. The negative energy escapes the white hole. So could white holes also reverse hawking radiate and get mass through this process. A... |
EM waves include both lower frequency(RF/microwave/mm -wave) and higher frequency(visible light).
My question is: why do these waves, whos behavior is governed by the same maxwells euqations, behave so fundamentally differently?
For example, you can accurately understand a scene using a camera which has been designed ... |
I am working on a project that involves launching a ball through a basket (similar to basketball, but on a smaller scale for now).
I haven't started building the project yet as I wanted to work out all the theory first. However, the system I am thinking of uses a single flywheel configuration, driven by a DC motor, th... |
in a material there is a quantity N of electrons, if light (of appropiate wavelenth) hits it, only the valence electrons will be removed from the material (photoelectric effect), how can I calculate the number of electrons removed?
I have seen in the forum that they respond to the number of electrons emitted per second... |
In the question I have L = 1 and s = 1/2. First I had to find the quantum state for the highest m = m$_l$ + m$_s$ value which I did. To find the quantum states for the next highest m value I used the lowering operator of j, as can be seen in the picture below. I understand that there has to be another state for that m ... |
Let us consider 't Hooft anomaly:
\begin{eqnarray}
Z[A^\lambda]=Z[A]\exp(i\alpha[A,\lambda]),
\end{eqnarray}
where $A$ is the background $G$-gauge field and $\lambda$ is some $G$-gauge transformation.
We know that a nontrivial factor $\exp(i\alpha[A,\lambda])\neq1$ obstructs $G$-gauging and, if the symmetry $G$ is a... |
For a standard $N$ DOF system we can find the eigenfrequencies and eigenmodes of the system by setting up an eigenvalue problem in the form of
$$
([M]-\omega^{2}[K])\phi=0.
$$
For a continuous structure, we can set up equations in some coordinate system and solve.
Consider a structure, such as a beam, vibrating near ... |
The formula is given by $n=\frac{1}{\sin(C)}$, $n$ is the refractive index of the denser medium, C is the critical angle. From this formula, it seems to be that we are substituting the angle of refraction as the angle of incidence, therefore $\frac{\sin(90)}{\sin(C)}$, but why can we do this? Why not $\frac{\sin(C)}{\s... |
In the dam scene in Episode 7 of Devs, one of the characters says:
A few moments from now, you climb over this rail, you stand on the other side and balance there, right on the edge of the dam. Just your toes on the concrete, arms outstretched not holding the rail. Whether you stay balanced or fall depends on quantum ... |
The quantum Hamiltonian of a degenerative parametric amplifier (DPA) is given by (taking $\hbar=1$
$$
\hat{H}=\omega\hat{a}^{\dagger}\hat{a}+2\omega\hat{b}^{\dagger}\hat{b}+\kappa\left(\hat{a}^{\dagger 2}\hat{b}+\hat{a}^{2}\hat{b}^{\dagger }\right),
$$
where $\hat{a} \ (\hat{a}^{\dagger})$ and $\hat{b} \ (\hat{b}^{\dag... |
Please consider me a beginner and not an expert by any means. My question below will thus be very very simple as that of an uninitiated. Let me consider four simple physical systems with ${\rm N}_S$ states. With those, I'll try to explain my current state of knowledge/understanding at this point and ask the question.
... |
An operator is said to be linear if it obeys the distributive law and commutes with the constant i.e.
$\hat{A}(a_1 |\psi_1\rangle + a_2|\psi_2\rangle)=a_1\hat{A}|\psi_1\rangle +a_2\hat{A}|\psi_2\rangle$ and same when we act in from bra.
The product of two operator are not commutative (not all case) but their product a... |
Consider a non-relativistic point particle of mass $m$ in 1D under the action of only conservative forces. Then by Newton's second law, the equation of motion is $$m\ddot{x}(t)=-U'(x(t)).$$
Now, do all potentials that satisfy $U(x)=U(-x)$ produce periodic motion? If so, how can we prove it?
It seems to be the case for ... |
The evidence for Big Bang cosmology is an expanding universe. The expansion of the universe is accelerating. Gravity causes acceleration. What evidence is there that proves everything is moving away from us and not us falling away from everything towards a spacetime singularity?
|
Why can't we feel any force unless that force is opposed by other forces ??
E.g. we don't feel our weight unless we stand on rigid bodies or other supports . When we are in air or when we jump from a height we feel weightless because there is no force opposing our weight.
So my question is why and how do such crazy th... |
An homogeneous sphere of mass $m$ and radius $r$ with only initial rotation $|\dot\phi(t=0)|= \omega_0$ is placed over an horizontal surface , with initial velocity of translation of the center of mass $\dot R(t=0)= 0 $. Until the sphere starts rolling without slipping,besides its movement of rotations, it must necessa... |
I want to start by prefacing a scenario. Say equation of state is $w<-1$ and we live in a phantom dark energy dominated universe. This means in a finite time the cosmological scale factor reaches infinity and the cosmic event horizon reaches 0 in a finite time (i.e. as $t \to t_{rip}$). The expansion then starts first... |
My cousin told me that inertia is just a pseudo force that act on a thing, because he said that inertia is the same as centrifugal force. But when I search for the true fact in Google, I found that inertia is real ? I'm confused, please clarify the true fact.
|
How can to derive $F = m H$?
I know:
$$ F = \frac{\mu m_1 m_2}{4\pi r^2}$$
$$\mu = \frac {B}{H} $$
$$ H = \frac{\mu m}{4\pi r^2} $$
where '$F$' is Force, '$H$' is Magnetic Intensity, '$\mu$' is permeability, '$m$' is pole strength, and '$H$' is Magnetic Field Intensity.
|
I have read here that mass is an invariant and that it is the momentum that approaches infinity when your speed approaches the speed of light. That is why infinite energy is required to accelerate an object to the speed of light.
But, why doesn't mass increase as velocity increases? I have read that relativistic mass i... |
In the derivation of the Lie algebra in the first volume of Quantum Theory of Fileds by Weinberg, it is assumed that the operator $U(T(\theta)))$ in equation (2.2.17) is unitary, and the rhs of the expansion
\begin{equation}
U(T(\theta)))=1+i\theta^a t_a +\frac{1}{2} \theta_b\theta_c t_{bc} + \dots
\end{equation}
requ... |
Let's say I have two iron plates (P1 and P2). I want one side of each plate to have an opposite charge.
The surface of P1 should be charged with a positive charge and that of P2 with a negative charge so when I bring the charged sides of two plates closer they should attract eachother. But inorder to achieve this there... |
I want to compute the conductivity of a complex scalar field in both the symmetric and symmetry broken phases. To define the current operator one needs to couple the matter field to EM gauge field using the minimal coupling, the action will be the famous GL functional:
$$ S=\int d^dx\,d\tau \left\{ |(\nabla-ie\mathbf{A... |
I was reading about the hypothesis advanced by George Chapline and Robert Laughlin that black holes might actually be 'dark energy stars', regions where spacetime has undergone a phase transition (e.g. this lay article and this paper).
Does the black hole image produced by the Event Horizon Telescope Collaboration fals... |
I'm a bit confused on the interpretation of the chemical potential in a canonical ensemble (a system which can only exchange energy with a reservoir but not particles).
Here is what I think I know:
As far as I understand, when one deals with a system that can exchange energy and particles with a reservoir one is deali... |
My nephew asked me to help him on his physics homework. I'm alright as physics, but it is by no means a strong point (it's been a looooooong time since I did any physics). He was presented with this diagram:
He had some simple enough questions such as "why does the light change direction" and "what happens when the li... |
The experiment is as follows
A solenoid is connected to a galvanometer and a magnetised iron rod is passed through it. (the apparatus is not ideal, and there is no zero error in the galvanometer)
I pulled the rod very rapidly out of the solenoid and stopped, i
observed that the needle of the galvanometer moved to the ... |
I have a few questions about differentiating the on-shell action.
Here is what I currently understand (or think I do!):
Given that a system with Lagrangian $\mathcal{L}(\mathbf{q}, \dot{\mathbf{q}}, t)$ has the coordinate $\mathbf{q}_1$ at time $t_1$, and the coordinate $\mathbf{q}_2$ at time $t_2$, there exists a uni... |
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