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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Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newtons third law and Momentum conservation. Here is what I have tried. Lets take $m_1$ (the ball) hits $m_2$ (the man). ...
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0answers
41 views

Commutation relation between linear momentum and vector Potential [on hold]

Does the linear momentum and vector potential commute? How can we show their commutation relation ? I am actually trying to find the commutation relation between both linear momentum of an electron ...
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2answers
126 views

In a CMCS 2-body system, why does the speed of the particles after collision stay the same?

A particle $m_1$ is traveling with velocity $v$ toward a stationary particle $m_2$. The velocity of the center of mass is given as $v_c=\frac{m_1}{m_1+m_2}v$. Changing to a moving coordinate system, ...
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2answers
60 views

Why are force, momentum, and kinetic energy derivatives of each other [on hold]

Force $ma$ is the rate of change of momentum, or the derivative of momentum with respect to time $$\frac{d}{dt} mv = ma = F$$. Kinetic energy is the integral of momentum with respect to velocity: ...
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0answers
17 views

system to reposition a car

I was thinking of a system that will use ejected gas/liquid to reposition the position of a car and/or assist in braking. Would such system be viable? What parameters would such system have? Ie. to ...
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3answers
1k views

In general, why do smaller guns have more felt recoil?

Why is recoil easier to control on a more massive gun compared to a smaller gun with the same bullet. Presumably the bullet leaves both guns with the same momentum, but the larger gun seems easier to ...
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4answers
192 views

A question about canonical momentum and arbitrariness for potential in magnetism

The following question confuses me: There exists magnetic field $B_z =- \beta x$ where $x > 0$, and a particle is incident from origin point $(0,0)$ with pisitive charge $q$, mass $m$, and ...
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1answer
40 views

When will a ball running between two downwards slopes stop going back and forth?

Two angles $a$ and $b$ meet at a point, making an angle $c$ between them. $a$ and $b$ are all $0 < \theta < π/2$. $c$ is $π/2 < \theta < π$ $a$ is to the left and opens to the left, $b$ ...
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2answers
103 views

Where does the equation $p=\frac{1}{c}\sqrt{T^2 +2mTc^2}$ come from?

Where does the relativistic formula $$p~=~\frac{1}{c}\sqrt{T^2 +2mTc^2}$$ come from? What is the derivation from Einstein's formula? $T$ is the kinetic energy $m$ is the mass $p$ is the momentum.
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2answers
247 views

Confused about elasticity and collisions

I was solving the following problem and the explanation to it confused me. There are two objects with mass $m$ and $M$, respectively. The object with mass $m$ has a velocity of $\sqrt{2gl}$ and ...
66
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9answers
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Can we theoretically balance a perfectly symmetrical pencil on its one-atom tip?

I was asked by an undergrad student about this question. I think if we were to take away air molecules around the pencil and cool it to absolute zero, that pencil would theoretically balance. Am I ...
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3answers
55 views

Does a gas in a container lose kinetic energy?

When a gas is in a container, it frequently collides with the container wall, exerting pressure. However, with a collision, kinetic energy ought to be transferred from the gas molecule to the ...
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0answers
25 views

Momentum Vectors (Physics 11) [closed]

This is a question regarding momentum and vector angles that I can't seem to solve. A 6 kg ball (A) moving at 3 m/s hits a 6 kg ball (B) at rest. Ball A moves 40 degrees to the left of its original ...
2
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2answers
155 views

How do waves have momentum?

A question on a practice test I'm taking is as follows: By shaking one end of a stretched string, a single pulse is generated. The traveling pulse carries: A. mass B. energy C. momentum D. ...
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3answers
54 views

Force to deflect ball colliding with wall

Suppose I have a ball with a certain coefficient of restitution. The wall can be considered indeformable and with infinite mass. Everything's in 3 dimensions, and the ball can hit the wall at any ...
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1answer
39 views

What does the second solution in an elastic collision represent?

A ball of mass 2 collides with a stationary ball of mass 1 elastically! In finding the velocities i end up with two solutions and am not sure how to understand the second solution Simplified ...
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2answers
69 views

Why does linear momentum change in this problem?

I found this problem in a Irodov's book. It's asked to find the momentum increment of the bullet-rod system. I wonder why the system momentum changes. They argue this: The bullet-rod system is ...
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5answers
4k views

Relativistic momentum

I have been trying to derive why relativistic momentum is defined as $p=\gamma mv$. I set up a collision between 2 same balls ($m_1 = m_2 = m$). Before the collision these two balls travel one ...
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3answers
1k views

Inertia Vs Momentum

At my recent lesson on kinematics, my teacher taught about inertia and momentum. This is what she said. Inertia: a characteristic of an object that resists changes to its state of motion. Momentum: ...
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1answer
48 views

Shooting a bullet in space [closed]

Imagine I was in space holding a gun and I shot a bullet from it. Do I go back? Or does the bullet move forward? Or both of us go in the same speed at different directions? Or what? Please Explain. ...
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1answer
132 views

Changing momentum of moving trolley

We have a trolley of mass $m$ and it is moving at a velocity $v$ along a smooth horizontal plane. It is full of water, and is leaking water at a constant rate out of the bottom of the trolley, i.e ...
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1answer
42 views

Force vs. Momentum [closed]

Obviously, if no external non-preservative force acts upon an object, if we apply a force to the object than the object will continue to hold that force within them. My question is, the object would ...
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3answers
98 views

What is the algebraic form of the momentum eigenstate?

I'm asking this in the context of trying to verify the equation $a^{\dagger}_{p} \vert 0 \rangle = \frac{1}{\sqrt{2\omega_p}} \vert p \rangle$. So far I have calculated $\vert 0 \rangle = ...
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2answers
153 views

What does the force mean in $dp/dt$ form?

One was to write Newton's laws is: $$F=\frac{dp}{dt}.$$ I don't understand what is the force there. I believe that $F$ is the net external force on the system. So supposedly I have a mass which is ...
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1answer
1k views

Do neutrinos refract?

The most benign of interactions is refraction. While neutrinos rarely interact with matter in a sense like the photoelectric effect, does that mean that they don't refract either?
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1answer
37 views

Momentum distribution function for a particle in a 1D box

In these notes on statistical thermodynamics (pp. 62), I encountered this [topic: particle in a 1D box]: We shall adopt the initial condition that the probability distribution function has the ...
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0answers
32 views

Does a graviton impart negative momentum?

Picture a massive system on an axis. If a graviton is generated and emitted by a system in the positive direction, will that system also be accelerated in the positive direction? Another system ...
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1answer
252 views

Symmetries of a Uniform Magnetic Field

Simple question. A system with a uniform electric field everywhere in space has translational invariance in the directions perpendicular to the electric field but no translational invariance parallel ...
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1answer
138 views

How is momentum conserved when a magnet attracts a metal?

Suppose your have any magnetic object and no external force acts upon it, and the object comes near a metal which causes an impulse (think that will happen). However, the magnetic force is internal to ...
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1answer
100 views

Equations for a collision between two particles

Say I have two particles on a 2D plane, they have a x and y coordinate, a x and y velocity, a mass, a coefficient of restitution and a coefficient of friction. What formulae would I need to determine ...
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1answer
35 views

Energy and momentum of a relativistic electron

The question is to find the magnitude, $p$ of the electron's momentum in the unit of MeV/$c$, given that the kinetic energy of the electron is 2.53 MeV. The answer provided by the book says, ...
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2answers
37 views

Velocity of Rocket Exhaust

i recently learned a bit of rocket propulsion.It wasn't much complex but was explained in simple terms.The only problem i had understanding it was that in calculating the thrust of rocket the velocity ...
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0answers
59 views

Probability flux

I was reading a text on Quantum Mechanics in which it said that $$\int{d^3 x \, j(x,t)} = \frac{\langle p\rangle}{m},$$ where $\langle p\rangle$ is the expectation value of the momentum operator at ...
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1answer
26 views

Comparison of the effects of collisions from an NFL Nose Tackle and a Car with roughly the same momenta

If you get hit an NFL Defensive Tackle who runs at roughly 17mph (7.6m/s) it'd hurt a lot, but if you got hit by a normal car at 1.3mph (about 0.6m/s) it hardly hurts at all, and a collision from an ...
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1answer
77 views

Uncertainty principle

I am reading about uncertainity principle. My textbook says, if $λ$ is the wavelength of the radiation used to observe the particle then the position of the particle cannot be determined with ...
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4answers
209 views

Why is the momentum of a particle $\gamma mv$?

I am very new to relativity, and as I was going through Resnick & Halliday, I saw that momentum was no longer $mv$, rather $\gamma mv$. This was the proof: $$p = mv = m \frac{\delta x}{\delta ...
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2answers
49 views

Human max speed in open space

Suppose you are an astronaut forgotten in the middle of nowhere, between our solar system and proxima centauri's. Now, you are out of fuel. I heard that with some kind of movements, someone in free ...
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2answers
90 views

Linear momentum experiment

trying to design an experiment for linear momentum. Could someone tell me whether this would work. Get a wooden toy car and attach it to some string which is hung over a pulley on the end of the ...
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2answers
4k views

block slides on smooth triangular wedge kept on smooth floor.Find velocity of wedge when block reaches bottom

Find the velocity of the triangular block when the small block reaches the bottom: Here is what I did: The final velocity(at the bottom)of the small block of mass m is $\sqrt{2gh}$ along the plane ...
2
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3answers
725 views

How do the electric or magnetic fields contain momentum?

I have recently come to know that the electric and magnetic field contain both linear and angular momenta, which are known functions of the electric and magnetic fields at any given point in space and ...
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6answers
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What is canonical momentum?

What does the canonical momentum $\textbf{p}=m\textbf{v}+e\textbf{A}$ mean? Is it just momentum accounting for electromagnetic effects?
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1answer
35 views

As the magnetic field propagates does it have a momentum that can be felt by another magnetic field of the same charge?

If I have a solenoid and a permanent magnet, and I placed the magnet an inch away from the solenoid, oriented in a position where the magnet would be repelled as the solenoid is turned on. Is it a ...
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2answers
144 views

Electromagnetic field or direct interactions between charged particles?

Consider a small distribution of charged particles enclosed by an arbitrary volume $V$ with boundary $S$. It can be shown that the total mechanical momentum of the particles, $\mathbf{P_{mech}}$, ...
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1answer
40 views

What is the difference between the momentum in the Fourier transform of a scalar field and the conjugate momentum of the field?

What is the difference between the momentum $p$ in $\exp(ipx)$ in the Fourier transform of a scalar field and the corresponding conjugate momenta $\pi(x)$ of the scalar field?
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2answers
50 views

Conservation of momentum and mechanical energy in different reference frames

I am a biologist developing an interest in physics. I am struggling with the implications of changing reference frames on momentum, mechanical energy and work done calculations. I invented the ...
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1answer
31 views

Momentum which is transfered to the wall of container by a molecule

now I study thremodynamics course, and I cant understand why for ideal gas in equilibrium state when a molecule collides with the wall of container it transfers to it the momentum which is equals to ...
2
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2answers
74 views

Momentum change of a photon upon diffraction at a grating

How is the momentum change of a photon is related to the grating periodicity and diffraction order? I came across with this question while studying surface plasmon polaritons (SPPs) and how to excite ...
4
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2answers
119 views

Is the Einstein Energy-Momentum equation $E^2 = p^2c^2 + m_0^2c^4$ valid only for Free Particles?

Is the energy -momentum relation $$E^2 = p^2c^2 + m_0^2c^4$$ satisfied only by free particles or even bound particles? Does the Energy refer to total Energy(including potential) or only (kinetic ...
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3answers
99 views

How can I find the angular and linear velocity of a 2D body that breaks into two bodies?

Afternoon. This is my first question, so do let me know if I'm doing anything wrong. Looking for help on building a 2D physics game engine with bodies that split in half: I have a two dimensional ...
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2answers
47 views

If one object, moving at a constant speed collides with another object - which is at rest - how much force has been applied?

This is one question for which an answer doesn't really make intuitive sense. In elementary school, we learn F=ma, but where's the "a" in a collision such as this? Edit: Plus, there has to be a force ...