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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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If system and block are released from rest, find the tension in string when the string is vertical [closed]

By using Work Energy Theorem, as well as Velocity of centre of mass, I succeeded in finding the velocities of both the ring as well as block. I noticed that there is going to be a vertical circular ...
Science Tard's user avatar
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Generate trajectory between 2 points to achieve a desired momentum [closed]

NOTE: This question is about generating trajectory between 2 points to achieve a desired momentum. I consider it as a topic for physics. I need to plan path for robotic arm(having a tennis racquet as ...
Pratham's user avatar
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Idealized Newton's cradle

I was wondering about the conditions for an ideal newtons cradle. Under regular circumstances, the collisions are inelastic and a newton's cradle dissipates energy in various forms like heat, friction,...
Ritesh Nandi's user avatar
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Why is it less shocking to cross the bump with just one wheel? [closed]

Difference between 'go over speed bump with one side' and 'both sides at the same time' I asked a similar question previously and received an excellent answer stating that when going ...
NOH WHIREA's user avatar
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Apparent violation of Newton's Third Law in relativistic force transformation

In special relativity, we know that, relativistic force is defined as F = dp/dt, where p = γmv. For forces perpendicular to the direction of relative motion, force transforms as F' = γF. Consider two ...
Kenshin's user avatar
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Direction of impulse

My textbook has the following problem: A batsman deflects a ball by an angle of 45° without changing the initial speed which is equal to 54 km/h. What is the impulse imparted to the ball? (Mass of ...
archthegreat's user avatar
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A 1m diameter sphere contains a Avagadro Number (mass 2.015g) of ideal gas particles of mean velocity 550m/s, what is the pressure in the sphere? [closed]

I get an answer of 1.552 kPa using surprisingly simple mathematics and wonder if my method is valid. I used P(sphere) = M(gas) * v(particles)^2 / r(adius sphere)^3 / 4 / Pi() Can it be that simple.
Bryan Major's user avatar
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Noether's theorem by a taste of logic [closed]

I am a mathematician and I asked this question briefly and my question became closed, may be - I don't know - because physicists don't used to apply the method of "proof by contradiction". ...
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How does the direction of the change in momentum of the object change during the motion?

In the case of an object's movement resembled in this graph, as the gradient is decreasing, a decrease in velocity occurs. According to the formula $$p = mv$$, The momentum is directly proportional to ...
Mohammad Osama's user avatar
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Alternative way to compute expectation value of momentum? [closed]

This might be ridiculously incorrect, but is it possible to find the expectation value of momentum like this? In the position space: $$\langle x | \psi \rangle = \psi(x)$$ $$\langle \hat{A} \rangle_{x\...
Aryan MP's user avatar
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Meaning of $d\mathcal{L}=-H$ in analytical mechanics?

In Lagrangian mechanics the momentum is defined as: $$p=\frac{\partial \mathcal{L}}{\partial \dot q}$$ Also we can define it as: $$p=\frac{\partial S}{\partial q}$$ where $S$ is Hamilton's principal ...
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How do you solve instantaneous 3 body collisions

A few years ago I built myself a very basic python program that did some very basic collision mechanics between particles with a mass and velocity and it was helpful in learning a few things and ...
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What's the meaning of the momentum operator?

I understand that a wave function $\psi(x, t)$ tells me that the probability to find the particle at position $x$ is $|\psi(x, t)|^2$. In the Schrodinger equation, we use the momentum operator $\hat{p}...
James's user avatar
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Could we deduce energy, momentum and angular momentum conservation laws from only Galilean relativity?

In Newtonian physics we could deduce conservation of energy, momentum and angular momentum from Newton's three laws. But by Noether's theorem, conservation laws could be deduced from symmetries. Could ...
moshtaba's user avatar
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Kinematics of a two-body decay [closed]

I suspect a flaw in the reasoning below, but am unable to pinpoint it: Is there something inconsistent in terms of the application of conservation of momentum and energy? Thanks for any hints in ...
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Do bodies stick together after an inelastic oblique collision?

My question is particularly about an oblique collision case. (For example a body having velocity along x axis approaching another with velocity along y axis) From what I know, in perfectly inelastic ...
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Linearity of Amplitudes and Lorentz Frames

I know that this question may be a bit weird, but I decided to ask. Assume I have an amplitude, say in QED, which depends on a set of four-momenta $\{p_1,\ p_2,\ p_3,\ ...,\ p_n\}$. Further assume ...
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Proper time of two particles being the same when they are under a tree-level interaction

I have a question: I have a figure like this: The interpretation of the diagram is this: a particle is emitted at $x_2$, interacts with the field at $x_1$ and from $x_1$ another particle is emitted ...
SX849's user avatar
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Does moving the idler in a wheel and disk CVT conserve energy or momentum? [closed]

Consider the wheel and disk CVTs (continuous variable transmissions) below. Configuration A comprises a CVT disk coupled to the "system under control" 's', whereby a control wheel 'cw' ...
Mr. Haelscheir's user avatar
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2 answers
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Generalized momentum

I am studying Hamiltonian Mechanics and I was questioning about some laws of conservation: in an isolate system, the Lagrangian $\mathcal{L}=\mathcal{L}(q,\dot q)$ is a function of the generalized ...
user1255055's user avatar
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After how many bounces will a ball's mechanical energy equal zero?

This was a question I asked myself for fun. It turned out to be more difficult than I initially imagined. The Problem: Let's say a ball is dropped from h0. Air friction is negligible. The collisions ...
jazzblaster's user avatar
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Problem when deriving formula of the momentum of photons in photoelectric emission

Now I know this might be a small error on my part or some wrong assumption taken, but for some reason when I tried deriving the momentum, I ended up with a different value. The momentum is given as: $$...
Aaron's user avatar
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Favre Averaged Navier-Stokes equations

Consider the Navier-Stokes (NS) equation \begin{equation} \frac{\partial (\rho u_i)}{\partial t} + \frac{\partial (\rho u_i u_j)}{\partial x_j} = - \frac{\partial p}{\partial x_i} + \frac{\partial}...
Somestudent01's user avatar
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Is it theoretically possible to aim a neutrino's trajectory without using a massive celestal body to aim it?

Recently, when reading about atomic rockets, I noticed an entry about spin-aligning neutrons to make them shoot out of the rocket's nozzle instead of randomly flying around to wreck the rocket. ...
General_Ripper's user avatar
2 votes
1 answer
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Momentum distribution of nucleons inside the deuteron (Paris potential)

I am looking for a graph that shows the momentum distribution of nucleons inside the deuteron. Side note: I know that several models for nucleon-nucleon potentials exist, such as the Paris, Bonn or ...
MCSquared's user avatar
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Energy and momentum operators using Hamilton's equations

The energy operator is: $${\displaystyle {\hat {E}}=i\hbar {\frac {\partial }{\partial t}}}\tag1$$ and the momentum operator is $${\displaystyle {\hat {p}}=-i\hbar {\frac {\partial }{\partial x}}}.\...
User198's user avatar
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Total momentum of a fluid in a pipe [closed]

Suppose we have a cylindrical pipe let's say length L = 10 m and radius R = 1 m through which water is flowing. The velocity distribution is given by Poiseuille's Law: $v(r)=\frac{\Delta P}{4L\eta}\...
Javieer Picazo's user avatar
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2 answers
79 views

Definition of expectation value for momentum [duplicate]

I think this is probably a stupid question but I'm confused over how the expectation value for momentum is calculated. It is always given as $$⟨𝑝⟩ = ⟨𝜓|\hat{p}𝜓⟩ = −𝑖\hbar∫𝜓^*(𝑥)\frac{d𝜓(𝑥)}{...
user1184477's user avatar
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Where did the rotational energy come from? [duplicate]

Consider a floating static pencil in flat space with no gravity. If we apply an impact force F for a short time t to the pencil vertically, pencil must get a CM momentum Ft, and corresponding kinetic ...
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How to understand $W=pc$ in Feynman's Lectures on physics?

Pictures below are from 34-3 of Feynman's Lectures on physics. I can't understand the red line. The $p$ is momentum, $c$ is light speed. I can't understand the red line. I feel the author think $pc$ ...
Enhao Lan's user avatar
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Difference of $p^0$ and $E_p$

In QFT when I learn about Feynman-propagator, I see such an expression: $$ \frac{1}{2E_p}e^{-iE_p(x^0-y^0)}=-\frac{1}{2\pi i}\int_Cdp^0\frac{e^{-ip^0(x^0-y^0)}}{(p^0-E_p)(p^0+E_p)}. $$ I know that ...
Gao Minghao's user avatar
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What is the so-called momentum density? [duplicate]

What is the so-called momentum density? I am reading the paper by Pitaevskii, in which he stated that it is well-known. He studied the nonlinear Schroedinger equation, but it seems that the concepts ...
poisson's user avatar
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Confusion in conservation of momentum [closed]

Two masses $m_1$ and $m_2$ are attached to the two ends of a rope that is sent through a pulley. Then a mass $M$ is dropped onto the mass $m_1$ from a $h$ height. So when the law of conservation of ...
Yara Try's user avatar
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2 votes
1 answer
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Catching a large reaction mass in space [closed]

Suppose we have a long, cylindrical spaceship in free fall in space. Another spacecraft is nearby for observing the cylindrical craft; also in free fall so we can determine when the cylindrical ...
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Can you make a car powered by 4 car air jacks? Using the mechanics of a manual pedal pottery wheel

If an air jack can pump up a car using little force, can’t an aluminum air jack spin a plastic wheel barrel car going at least 10 mph? Each wheel will have an air jack that uses the mechanics of a ...
DevGabe's user avatar
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1 answer
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Wavefunction with determinate momentum

In page 100 Griffiths' Introduction to Quantum Mechanics, Griffiths states that the eigenvector of $\hat{p}$ in the position basis is $\frac{1}{\sqrt {2\pi\hbar}}e^{\frac{ipx}{\hbar}}$ and states that ...
xyz1234's user avatar
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3 answers
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Conservation of momentum in Newton's cradle

Imagine a Newton's cradle with 5 balls with mass of each ball is $m$. In a case where two balls are dropped against three balls, if we write an equation considering that momentum is conserved, $$ 2mu=...
Yara Try's user avatar
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0 answers
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The little group of the connected Lorentz group [duplicate]

For $n\geq 2$, the $n$-dimensional connected Lorentz group is defined as $$SO(n-1,1)^{\uparrow}=\{f\in M_n (\mathbb{R}):f^T\eta f=\eta, \det (f)=1,f^0_0>0\}$$ where $$\eta=\begin{bmatrix}-1 & ...
Mahtab's user avatar
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-1 votes
1 answer
108 views

A car collides with a fast-moving bus, which vehicle experiences the greater change in momentum? [closed]

$\textbf{My question:}$ A car collides with a fast-moving bus, which vehicle experiences the greater change in momentum? But when I googled I got conflicting answers from "expert answers": ...
Reuben's user avatar
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1 answer
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Conservation of $y$ component of momentum

Rain with mass $mr$, falling vertically downwards at speed $v$, into a truck of mass $mt$, moving on a horizontal surface at speed $u$ inital, ignoring friction and air resistance. Taking the system ...
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How to interpret the additive term in torque formula?

Torque formula for a body subjected to a force is: $\vec{M}$ = $\frac{\mathbb d\vec{L}}{\mathbb dt}$ + $\vec{v}_o$ $\times$ $\vec{p}$; where $\vec{M}$ is the torque, $\vec{L}$ is the angular momentum, ...
bnim's user avatar
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1 vote
4 answers
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Question about relativistic mass and momentum transfer of Light

How can we reconcile the concept of inertia, typically associated with mass, with the behavior of light or electromagnetic waves, which lack classical mass but still exhibit resistance to changes in ...
Shantanu Binekar's user avatar
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Pure rolling interrupted, does friction provide impulse?

When a ring is under pure rolling (no slipping and friction zero) on a horizontal rough surface and now another small ball hits it, can there be impulse due to friction? I feel that there should be ...
Anon's user avatar
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1 answer
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"Momentum" of spinning disc from collision -- conserving momentum of input momentum?

I have an application for which I have concluded a collision lets conserve momentum. Examples of the type of scenario in which I believe my conclusion applies: a waterwheel blade hit by a ball (wheel ...
user5588495's user avatar
5 votes
3 answers
350 views

Is invariance under rescaling of the Lagrangian lost during quantization?

In classical mechanics, a field theory can be described by a lagrangian involving the field and its derivatives, $\mathcal{L}=\mathcal{L}(\phi,\,\partial\phi,\,t).$ The equations of motion for the ...
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2 answers
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Ball colliding with inclined stationary plane

A particle with mass m1 is dropped from a height onto an incline plane creating the angle $\alpha$ with the ground (the slope is frictionless). The coefficient of restitution is e. Find the angle $\...
Alexander Jonsson's user avatar
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2 answers
111 views

Why $\int_{t_0}^{t_1} \mathbf{F}dt\neq \mathbf{P}(t_1)-\mathbf{P}(t_0)$ in general?

I'm reading the book of mechanichs of Kleppner & Kolenkow and I can't understand the following passage Why it is essential to deal with the same set of particles? This makes no sense to me, as ...
Masacroso's user avatar
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2 answers
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Would placing sand bags over the top of a car's strut housing reduce the jarring impact felt when the car hits a pothole? [closed]

I live in an urban area where many of the streets have pot holes and some of these streets have some very large and deep potholes. I have been wondering lately if it would be worth the effort to try ...
user57467's user avatar
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1 vote
1 answer
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Im confused on how conservation of momentum works mathematically for a problem involving a skater throwing two weights from rest [closed]

Here's the question. A 40-kg skateboarder on a 3-kg board is training with two 5-kg weights. Beginning from rest, she throws the weights horizontally, one at a time from her board. The speed of each ...
Groggyboi's user avatar
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How to show that $G_p=SO(D-1)$?

Let $G=SO(D-1,1)^{‎\uparrow‎}$ be the connected Lorentz group. Let $p$ be a timelike momentum with $p_0>0$. I want to show that $G_p=SO(D-1)$, the little group of $p=(M,0,\ldots,0)$ where $M>0$....
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