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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Application of Heisenberg's uncertainty principle on photons

While I was hobby-reading about quantum mechanics I came across Heisenberg's theory. But while I was trying to understand it I thought of this: if the speed of light (as well as the momentum of a ...
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Atmospheric pressure's effect on sound

An argument has been travelling in amongst my friends around this matter and after listening about it for 3 whole days I decided to ask it here. The Question is: Would a high atmospheric pressure ...
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103 views

How does a pop pop boat work?

I have been reading about the pop pop boat on wikipedea. What I don't understand is after the hot water is ejected the vacuume gets created, so when the same amount of water will be sucked in the boat ...
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53 views

Elastic Collision of Infinitely Large Body and an Infinitely Small Body

So I guess this is a somewhat conceptual question. There are two bodies, one with a mass $m$ that is so light it is massless and at rest so $v_{_i1} = 0$ And the other with mass $M$ that is almost ...
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95 views

Operator algebra for momentum and magnetic vector potential

Let $\vec{A}$ be the magnetic vector potential and $\vec{p}$ be momentum. $$ \vec{p} \cdot \vec{A} \psi = (\vec{p} \cdot \vec{A}) \psi + \vec{A} \cdot (\vec{p} \psi) $$ $$ \vec{A} \cdot \vec{p} \psi =...
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47 views

How impulse relates to momentum? is this correct?

Knowing that: $$F=\frac{dp}{dt}$$ I manipulate the equation a bit to say: $$Fdt=dp$$ Then ingrate both sides... $$\int{F}dt = p$$ From what I've read, isn't the change in momentum related to the ...
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126 views

What happens when two bodies collide in a dynamics point of view?

I'm a high school student learning about energy and momentum. What confuses me is the things with elastic and inelastic collisions. I completely (in my opinion) understand those concepts in energy ...
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1answer
35 views

How do i find how long an object can coast for?

I am given the mass of an object (a motorcycle), its velocity, the mass of its wheels, and the radius of the wheels. If the object rolls without slipping, how can I possibly find out how high it can ...
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61 views

Momentum Equation VS Momentum of Momentum Equation

Newton's second law states that the linear momentum ($P$) rate is equal to the net force: $$F=\frac{d}{dt}P \tag{1} $$ On the other side, there is a same expression for angular momentum ($L$): $$M=\...
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144 views

Conservation of mechanical energy isn't giving me the right answer? [closed]

I have been trying to solve this question: You are working for a shipping company. Your job is to stand at the bottom of an 8.0 m long ramp that is inclined at 37 degrees above the horizontal. You ...
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4answers
463 views

A question about $E=pc$ for massless particles

Since photon has no (rest)mass and $$E^2=(pc)^2+(mc^2)^2$$ we derive that $E=pc$ for particle with no (rest)mass. However, if we transform the non-relativistic formula for kinetic energy $$E_k=\...
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Do particles also have intrinsic linear momentum (linear analogue of spin)?

We know from quantum mechanics that microscopic particles have spin, which is a kind of intrinsic angular momentum. The particle has angular momentum without physically rotating. In a similar way, do ...
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53 views

Law of conservation of momentum , elastic collision [closed]

In Law of Conservation of momentum , elastic collision occurs only in an isolated system. A case defined as,when Object A comes with initial velocity and collides with object B which is in rest V= ...
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1answer
34 views

Rigid Balls aligned along a line in vacuum

Recently I've been trying to visualize a situation where i have these really rigid identical balls aligned along a line so close to each other in vacuum.Now if I were to apply an impulsive force to ...
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2answers
176 views

Is the reaction force for a stone hitting a wall infinite?

Let us assume a rigid stone which moves in empty space with a constant speed of $v$. (Or in the air with no friction and drag or you can imagine a free fall with friction). This stone hits a rigid ...
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0answers
17 views

Motion in Spaces [duplicate]

How does a shuttle move in the space as, the whole mechanism of a rocket is based on 3rd law of newton but, we can not apply 3rd law of newton in space because there is no reactive force in space?
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3answers
170 views

Derivation of momentum operator

From a video lecture on quantum mechanics at MIT OCW I found that you didn't need to know Schrödinger's equation to know the momentum operator which is $\frac{\hbar}{i}\frac{\partial}{\partial x}$. ...
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2answers
83 views

Conflicts between Bernoulli's Equation and Momentum Conservation?

The well known Bernoulli's equation states that $P+\frac{\rho V^2}{2}=c$ However, a simple momentum conservation considering $P_1$ and $P_2$ acting on two sides, and velocity changes from $V_1$ to $...
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2answers
112 views

How can photons cause charges to attract? [duplicate]

Photons are the force carrier of the electromagnetic force. I do not see how this could result in a transfer of momentum that attracts objects together. I am primarily interested in an intuitive ...
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1answer
96 views

When are energy, mechanical energy, momentum, and angular momentum conserved?

I am in AP Physics and my only real hangup is knowing when the said quantities are conserved. Please define what is the SYSTEM in your answer. I kind of have the basic idea. For example, if there ...
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0answers
23 views

How is conservation of momentum preserved in antimatter annihilation? [duplicate]

If an anti-proton collides with a proton, they are supposed to totally annihilate each other, correct? Then how is conservation of momentum preserved? Could you launch both protons and antiprotons ...
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40 views

Will the flash light accelerate in space? [duplicate]

As we know from school physics course light has pressure. So my question is will flash light accelerate in space in the direction opposite to light emission? If not, then will flash light with ...
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2answers
70 views

Which has the larger change in momentum [closed]

This is a concept question in my physics class, It isn't for marks, its just to gauge your understanding of the subject. I'm not sure if I have the right idea. since the mass of block A is 4 times ...
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1answer
53 views

Simple frame of reference problem (conservation of momentum?)

I'm having trouble wrapping my head around a particular concept. Suppose we have a machine that fires balls of speed $u$ at some mass rate $\sigma$ (of units $\frac{kg}{s}$) directly at a car of mass $...
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42 views

Relativistic momentum (Lorentz boost) low velocity expansion

If I have a momenta $p^{\mu}=(E, p_x, p_y, p_z)$ and transform it via lorentz boost in x-direction with velocity v I'll get for the new 0th component $E'=\gamma E + \gamma v p_x$ why is this in the ...
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69 views

Momentum operator derivation in QFT from QM

In David Tong`s QFT notes there is a chapter about the derivation of the momentum operator from quantum mechanics (page 44) where he is showing that the momentum operator can be expressed by the ...
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What is the effective electron mass in a plasma?

Is there a way to calculate the effective electron mass in plasmas? Effective electron mass is usually defined as varying from the vacuum electron mass in solid state physics. However, momentum ...
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Matter waves and de Broglie wave length

The wavelength of a particle of momentum p is calculated using De Broglie relation. The de Broglie relation was postulated for what is called a matter waves. Now according to the statistical ...
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3answers
254 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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1answer
39 views

Conservation of momentum in inelastic conservation

Why does momentum and velocity change along contact normal but not contact tangent In in elastic collision? Suppose a ball strike an inelastic surface. It's velocity component does not change along ...
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5answers
515 views

Can a balloon be used as an anchor point for a pulley?

For a physics/ engineering contest, I want to use a large balloon as an anchor point for a pulley. This would allow me to raise and drop masses. However, in testing, when I pull on the pulley the ...
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4answers
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Why do we need the quantity momentum?

Why do we need the quantity Momentum in physics when we have the quantities like Force and Energy? Isn't it possible to substitute the usage of Momentum with equivalent of Force and Energy?
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Calculating the force $F$ for wich $S_2$ will be in uniform motion

The sketch is given: The double pulley groove of radius $r=5\;\mathrm{cm}$ and $R=10\;\mathrm{cm}$ is in rotation Two inextensible wires of negligible masses are wound around each ...
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Does a conservation of momentum problem need to specify velocity, not just speed?

Problem: A $100$ g bullet is fired from a $10$ kg gun with a speed of $1000$ m/s. What is the speed of the recoil of the gun? This problem can be solved, if it can, using the law of conservation of ...
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3answers
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Derivation of $E=pc$ for a massless particle?

In classical mechanics, massless particles don't exist because for $m=0$, $p=0$. The relativistic relation between energy, mass and spatial momentum is: $E^2= (pc)^2 + (mc^2)^2$ . So it is said that ...
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What is the definition of linear momentum?

Every where and book I search I get that the definition of linear momentum is the amount of speed (quantity of motion) contained in it or simply it is mass $\times$velocity? So, what is an ...
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1answer
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Does third law of motion apply to light or EM waves? [duplicate]

Third law of motion - "For every action there is an equal and opposite reaction" I was considering the situation, where I may be motionless in space with only a flashlight and no forces acting on me. ...
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4answers
200 views

Calculating $\langle x | \hat{x} | p \rangle$ in $p$ basis

I am trying to calculate $\langle x\ |\ \hat{x}\ |\ p\rangle$. I can work in the $x$-basis like so: $$\langle x\ |\ \hat{x}\ |\ p\rangle=\int dx'\langle x\ |\ \hat{x}\ |\ x'\rangle\langle x'\ |\ p\...
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How to construct the radial component of the momentum operator?

I'm having trouble doing it. I know so far that if we have two Hermitian operators $A$ and $B$ that do not commute, and suppose we wish to find the quantum mechanical Hermitian operator for the ...
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1answer
253 views

Expectation value of momentum in any bound state [duplicate]

How do we prove that the expectation value of momentum operator in any bound state is zero ? $$ \langle \hat{P} \rangle_{\text{bound state}}=0 $$ and what about the position expectation value ? How ...
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1answer
223 views

Optimization of Bottle Rocket Water Level

My (entry-level) physics class is building bottle rockets, and we are competing to build the longest-flying bottle rocket. The rockets are filled partway (we get to decide how much to fill them) with ...
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1answer
23 views

For elastic collisions, can I transfer mass to velocity?

I think my teacher said that because the momentum is the same if you multiply/divide mass and velocity by the same factor, you can make the masses equal and then do a shortcut. Is this right?
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Conservation of momentum homework problem [closed]

A 2-stage rocket travels $1200 \text{ m/s}$ relative to earth. When the first stage runs out of fuel, the explosive bolt separates the first stage from the second with a velocity of $35 \text{ m/s}$ ...
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2answers
309 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 ...
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2answers
113 views

The acceleration of the centre of mass [closed]

Given two balls that are thrown straight up in the air at a speed of $40 \:\mathrm{m/s}$, $0.10 \:\mathrm{s}$ apart. One ball is twice the mass of the other. The heavier ball is thrown second. I'm ...
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31 views

Impulse and Momentum

Case 1- We have two masses of equal size. Mass 1, with positive velocity, collides with Mass 2. This causes Mass 1 to have 0 velocity in the end and Mass 2 to have a velocity. Case 2- A mass (1) ...
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171 views

Relation between $\Delta E$ and $\Delta p$

This will be a very quick question. I've seen in some books, that when describing the Heisenberg uncertainty principle, it was used implicitly the application of the following statement: $$\Delta E=\...
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2answers
161 views

Particle anti-particle annihilation and photon production

This is just a conceptual question I guess. The annihilation of a particle with a finite mass and its anti-particle cannot lead to the emission of only one photon, and this is due to the conservation ...
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2answers
882 views

Why the photon can't produce electron and positron in space or in vacuum?

$$\frac{hc}{\lambda} = K_e + K_p + 2m_e c^2$$ could be the energy conservation equation for a photon of wavelength $\lambda$ decaying into a electron and positron with kinetic energies $K_e$ and $K_p$ ...
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2answers
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Pair production - mathematically?

Allover the web i am only seeing a statement similar to this: Pair production is not possible in vaccum, 3rd particle is needed so that conservation of momentum holds. Well noone out of many ...