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Questions tagged [momentum]

In introductory mechanics, the momentum of a particle is its mass times its velocity. In electrodynamics, the momentum of a field is proportional to the cross-product of the electric field with the magnetic field. In special relativity, momentum is generalized to four-momentum.

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Momentum Four-Vectors particle physics

I am studying Special Relativity, and am really struggling to get my head around four-vectors. I am looking at the following question. You have a particle of rest mass M and total energy E, which ...
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Disk and stick Collision involving conservation of angular momentum

A 2.0kg disk traveling at 3.0m/s strikes a 1.0kg stick of length 4.0m that is lying flat on nearly frictionless ice. The disk strikes at the endpoint of the stick, at a distance r=2.0m from the center ...
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Is acceleration of particle by photon a continuous process?

There are a lot of questions, so I assigned a number to each one. Let's assume we have electron which is not moving in some inertial frame of reference. Let this electron be hit by a photon. Since ...
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Most of the momentum of a proton is carried by the quarks

I saw this in wiki https://en.wikipedia.org/wiki/Antiproton#Modern_experiments_and_applications "the valence quarks in the proton, and the valence antiquarks in the antiproton, tend to carry the ...
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Why are the vectors canceled out in this scenario for angular momentum of a particle?

I have a study guide for our next test, and I'm trying to understand the professors answer but I don't understand why i^ * i^ = 0? Here is his work, Why do we know that the P Vector is on direction ...
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Physical Interpretation of Energy-wavenumber Graphs

Consider an energy-wavenumber graph, typical in solid state physics, like the one below. I can follow the mathematics in the derivations with a KP model. But I don't understand the physical ...
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Doubt from Momentum operator in the position basis [duplicate]

J.J Sakurai shows in the section of ' Momentum operator in the position basis' as $$P \lvert\alpha\rangle = \int dx^{'}\lvert\ x{'}\rangle\Bigl(-i{h\over 2\pi} {\partial\over\partial x} \langle\ x{...
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Forces on Colliding Blocks [closed]

A block of mass $m_1$ travelling at velocity $v_{1\ pre}$ collides with a block of mass $m_2$ travelling at velocity $v_{2\ pre}$. Both travel along the same axis and experience no external forces (...
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What experiment would confirm De Broglie equation on photons?

If we want to check experimentally that, for a photon: λ=h/p (De Broglie equation) Has such experiment been carried out? What is/would be the experimental setup? Wikipedia doesnt show such protocol ...
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Momentum Operator on a Riemannian Manifold

Consider a non-linear sigma model on a Riemannian manifold with metric $g_{ij}$ with the action $$S= \frac{1}{2} \int dt g_{ij}(X) \frac{dX^i}{dt} \frac{dX^j}{dt}.$$ The momentum operator is $$P_i= \...
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Why is momentum not conserved in this particle interaction?

In this particle equation. $$\Lambda^0 \rightarrow n$$ I thought it would be possible to conserve momentum as the neutron could carry on in a straight line and adjust its speed accordingly so the ...
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Conservation of angular momentum with a circular disk and a person at the rim

So, I was reading my textbook in the section regarding net torque, and they gave an example of a seesaw with one person at each end, and they said that there is a net external torque due to the force ...
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What is the physics behind a pirouette?

Around last week, I watched a ballet production at the Melbourne Arts Centre, and boy was I amazed! These people dressed up in costumes were spinning on their toes in all kinds of ways, and I was ...
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Life physics: falling objects

I've started wondering for a while WHY we experience so much damage when we hit a ground after a free fall? What forces are responsible for that? After some thinking I concluded that it has to do ...
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Claim that DeBroglie relation doesn't work in crystal

In this Wikipedia article on Position and Momentum Space, https://en.wikipedia.org/wiki/Position_and_momentum_space there is a claim that "the de Broglie relation is not true in a crystal" in the ...
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How are classical and quantum momentum related in an intuitive manner?

I know that quantum momentum is inversely proportional to the wavelength of the probability or matter wave of a given particle, but I don't get how this relation of this abstract mathematical ...
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Special Relativity; 3 Momentum Conservation

In SR, I understand you can use 4 momentum conservation, but what are the special cases where you can use 3 momentum/energy conservation? An example I have seen is with $$P_1=(M_1, 0) \\ P_2=(M_2,0) \...
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Change in momentum for gas particle collision with wall

I've attached the question as an image below as it's a graphical question. It simply states: "The diagram shows a gas particle about to collide elastically with a wall. Which diagram shows the ...
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What happens when in space a basketball flies and hits another resting basketball?

We have the following situation: In space, a basketball flies and hits another resting basketball. What happens next? a) Both balls fly in the original direction (but slightly slower) = momentum ...
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LSZ reduction, momentum diagram, QFT

I was initially confused about which way to choose the sign of the momentum, since it gives rise to different exponential momentum combinations and thus different deltas for momentum conservation. I ...
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Necessity to consider the square of Four Momentum

Why do we often need to consider the square of four momentum transfer $Q$ in scattering experiment or particle physics/cosmology instead of just the $Q$ itself?
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Why can we parameterize a null geodesic such that its velocity is four-momentum? [duplicate]

One principle in general relativity is that the wordlines of massless particles are null geodesics. It also seem to be a commonly stated fact (for instance see eq. (3.62) in Section 3.4 of Carroll's ...
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Individual air molecule momentum exchange

Background: Looking at this illustration about solar radiation pressure on a perfect reflective surface, incident photon exchanges its momentum to the slanted surface which provides a reaction force ...
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Net Force regarding Impulse and Momentum

I'm just going to preface this with: I don't know much, I've just started learning about impulse. Question: If there is a change in velocity regarding momentum $P$ then would there be a net force on ...
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What is the 4-momentum of a moving photon with a certain energy in natural units?

If a photon is travelling along the x-axis with an energy $E$ then the 4-momentum of the photon in natural units is: $$\begin{pmatrix}E \\E\\0\\0\end{pmatrix}$$ I don't understand why the first ...
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Itzykson & Zuber: Conjugate momentum sign

I can't give myself peace on a confusion about the signs. I'm studying on Claude Itzykson & Jean-Bernard Zuber, Quantum Field Theory, Dover Publications. Metric convention $g_{\mu\nu}=diag(1,-1,-1,...
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Collision angle relation to velocity of balls in Billiard Pool Game

I have a question about the billiard game physics. I know that in a billiard game, balls collisions are elastic and therefore the angle of the collision of two balls can easily be calculated no matter ...
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Energy conservation in a ballistic pendulum

So I was thinking about this really simple situation and then I came across a little question. The situation is as follows: There is a block of wood suspended from a ceiling like support with four ...
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Why does leaking truck keep same speed? [closed]

Why this is the right answer? As we know liner momentum is conserved so: $$V_1 M_1=V_2M_2$$ and since truck is leaking oil $M_2$ is less than $M_1$, let $M_1=10$ and $M_2=8$ then $$V_1\cdot10=V_2\...
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Transformation connecting two representations - Quantum mechanics [duplicate]

I am working on Dirac's paper The Lagrangian in Quantum Mechanics. He looks for the analogy between a classical transformation between two sets of coordinates and momenta $p_r$, $q_r$ and $P_r$, $Q_r$ ...
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CFT in momentum space

Is there a way to see the conformal symmetry in momentum space in a CFT? I mean if I can recover the conformal group in some way in momentum space.
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Simple harmonic motion momentum leads restoring force by 90 degrees [closed]

What is meant by "in a simple harmonic motion, momentum leads the restoring force of elasticity by 90 degrees" ??
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A basic formula of 1D elastic collision derivation

I found the folowing formula for 1d elastic colition: $$v_1 +u_1 =v_2+u_2 $$ (v,u means the velocity before and after the collision respectively) I tried to derivate it from momentum and energy ...
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If F(action) =F(reaction), why doesn't a ball bounce to its original height? [duplicate]

This might seem like a very absurd/ridiculous question, but this question suddenly popped on my head a few days ago. Is it that I'm missing something as I haven't reviewed this topic for quite a while?...
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Linear and angular momentum

If I push on an object not through the center of mass, we say that the translational effect on the entire object is the same. In other words, we can turn that off-center force into a force through the ...
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Why the lens is pushed to the right after light goes through?

I am asking myself why the lens must be pushed to the right in the following scenario: (image coming from Atoms and Sporks' nice video https://www.youtube.com/watch?v=UAmdoOX3870&t=327s) This can ...
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How momentum is conserved when left circularly polarized light hits a mirror?

I read that 2 light planes with same amplitude are set perpendicular to each other will create a circularly polarized light, but I am curious that when it is reflected back and is converted from left ...
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Why we get relativistic momentum without length contraction?

My last question was wrongly duplicated. We've already known that "p=γmv" . v is particle's velocity depends on our rest frame and mass too. But shouldn't we consider particle's momentum by its ...
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How can we write relativistic momentum without length length contraction? [duplicate]

We've already known that "p=γmv" . v is particle's velocity depends on our rest frame and mass too. But shouldn't we observe particle's momentum by its displacement? for particle's view, displacement ...
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Marble rolling further the more marbles rolled at it

Recently, our science teacher had us do an experiment at school, which was a form of Newton’s Cradle. Marbles were placed on a chain of rulers with grooves and a number of marbles were rolled at the ...
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Is static pressure the pressure used in the navier-stokes equations?

I believe in the image below, the pressure (P) being quoted is the same type of pressure that is used in the navier-stokes equations. Is this pressure the static pressure of the fluid? i.e. if i were ...
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Momentum of solar panel after photon is absorbed [closed]

A solar panel installed on a car of mass 1 kg lying on a friction free road. Let the efficiency of the solar panel be 100%.let the momentum of photons be $m_o$ and and the car be at rest before ...
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Is the radial component of $p^2$ a hermitian operator?

The kinetic energy of a system $p^2/2m$ in real space representation takes the form $-\hbar^2\nabla^2/2m$. I want to express this in cylindrical coordinates via the representation of the laplace ...
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Lie algebra vs. position and momentum commutators

Most theoretical texts on high energy physics make statements like below: $$[A_i , A_j] = i C^k_{i,j} A_k $$ (I suppose $\hbar$ may or may not be needed) and of course they describe this as being ...
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How is energy conserved in an elastic collision between two unequal masses?

In an elastic collision between two masses, if one mass is much heavier than the other, then the heavier mass will continue to move with same velocity while the lighter mass doubles its velocity. How ...
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Force on trapezoidal tank

I'm stuck with this problem that I have almost solved but the last bit seems impenetrable. Please take a look at the problem on the image i provided. Plan: I started by calculating the momentum flow ...
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Mossbauer effect: neglectable recoil or absolute no recoil?

I stumbled on the Mossbauer effect. From the wikipedia article, I cannot tell for sure if the momentum of recoil is really zero, or only neglectable. From what I do (think I) understand, the ...
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Derivation of the wind load formula

I am trying to derive the wind load formula: $F_d = \frac{1}{2} \rho v^2 A C_d$ in which I assume the drag coefficient to be equal to 1. My starting point is that the momentum of a rectangular wall ...
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How we can prove that photons have no mass? [duplicate]

I am thinking nowadays that how its possible that a particle without mass, actually exists? in the case of light its used to say that photons have no mass no weight but they have momentum. can any ...
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Momentum and changed a changing mass

let there be a spaceship which is floating in space with a surface size of A. The spaceship floats in a constant speed of $v_0$, dust with density of $\rho$ gets stuck on the (only) surface of the ...