# 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 ...
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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 ...
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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,...
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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 ...
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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 ...
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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 ...
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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.
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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 ...
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### Favre Averaged Navier-Stokes equations

Consider the Navier-Stokes (NS) 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}...
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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. ...
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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 ...
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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 $pc$ ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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### 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": ...
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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, ...
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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 ...
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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 ...
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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 ...
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### 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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