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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What would happen if light was converted into matter as it is propogating?

If light is a form of energy and can be converted into matter then does light slow down since no mass full object can reach the speed of light
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46 views

Conservation of momentum for moving inclined plane

I'm confused about the conservation of momentum in problems involving inclined planes that moves. Consider an inclined plane free to move on the floor and a body on the edge, there is no friction at ...
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3answers
112 views

Does the canonical commutation relation relate to the fact that momentum is the generator of spatial translations?

In classical mechanics momentum is the generator of spatial translations. This remains true in quantum mechanics. The way we define the momentum operator in one-dimension, for example, already shows ...
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91 views

Can a coffee cup really jump off the table?

I've been reading Nassim Nicholas Taleb's book The Black Swan which largely concerns the uncertainty of social and economic systems (and the futility of predicting outcome); the Black Swan being the ...
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0answers
29 views

Analogy Between Momentum and Faraday's Law of Induction

What is the reason behind momentum, during acceleration? Mass resist velocity change during acceleration similar to Coiled wire resisting Current amount change. The similarity is worth looking at. ...
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1answer
26 views

Get a ball to keep jumping using momentum, and force if necessary

To make a ball keep bouncing with momentum, or with force. When a bouncy ball hits the ground, the ground takes some of the momentum. But it doesn't disappear. Would you be able to make the ball keep ...
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69 views

How is momentum conserved in magnetic field? [duplicate]

In a uniform perpendicular magnetic field , force on charged particle cause change in direction of momentum. How do we explain it using conservation of momentum? I don't know what is Hamilton or ...
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149 views

Does the Inertia of a Cue Ball Affect its Reflection Angle off a Resting Billiard Ball?

Consider the following Diagram in which a Cue Ball (A) of mass M is shot twice at another pool ball with identical mass M. When the force with which the cue ball (A) is hit (v1) is increased (v2) ...
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40 views

Torque at a bar [closed]

Take a look at the image below. At the point B a motor is spinning really fast in anticlockwise direction. The motor should be connected to a propeller (I didnt draw it) that will pull the bar upwards ...
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32 views

How does the deflection of force on a tire work?

So, considering the example of a car that is turning, is all the force lost that's not along the axis of rotation of a tire, or is there some way to calculate how much of that force gets deflected ...
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4answers
172 views

Does the physical cross section of a projectile have an effect on the motion of a target? [closed]

Why can a baseball (moving with kinetic energy) move a baseball glove (or how a hammer displaces a nail),. yet a bullet can't move a person? I know the laws of conservation of energy, deformation, ...
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1answer
44 views

Derivation of de Broglie's Equation

I came across the derivation, present all across the web, which utilized Einstein's energy mass equivalence equation and energy of a photon. It goes like this: $$ E = mc^2,\;\;E = h f \;\;[f = ...
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61 views

Total Momentum in the Center of Mass Reference Frame

For solving problems involving elastic collisions it is useful to use the center of mass reference frame as to avoid quadratic equations. However, I am confused about why the total momentum in the ...
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5answers
294 views

How does constant thrust avoid quadratic kinetic energy accumulation?

I haven't found the right search terms for this question, so if it has been answered, references would be welcome. Suppose we start from experimental station in deep space (interstellar space if need ...
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1answer
25 views

Lorentz Force and Apparent Conservation of Momentum Violation Useful for Unidirectional Force?

My understanding is that the apparent violation of Newton's Third Law by the Lorentz Force necessitates a description of the system that describes the "missing" momentum as being absorbed/carried by ...
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1answer
40 views

Change in momentum in a photon collision?

Let's say I drop a ball on the ground and it bounces up. According to classical physics, once the ball hits the ground it goes trough a short phase of deceleration until the velocity reaches zero, ...
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2answers
47 views

Can wind be defined as momentum/mass of air molecules?

In the past I thought a breeze of wind was "made" from a large amount of air molecules going all the same direction in the same speed. But it's not like that, actually this voted answer, this site, ...
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62 views

Do gravitational waves contain actual energy and momentum? [closed]

Gravitational waves are waves in the fabric of space time and gravity is also caused by warped space time. So do gravitational waves contain actual energy and momentum?
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0answers
16 views

deformation and displacement by a collison? [duplicate]

In an experiment by Emilie du chatelet metal balls were dropped from a height on a clay bed only to find that the displacement of the clay material was proportional to the square of velocity of the ...
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0answers
31 views

Relationship between impact crater properties and kinetic energy? [duplicate]

William Gravesande in 1722 published an experiment in which brass balls were dropped from varying heights onto a soft clay surface. He found that a ball with twice the speed of another would leave an ...
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0answers
35 views

Separation of two particles

An object ofass $5$ kg is projected with a velocity of $20m/s$ at an angle of $60degress$ to the horizontal. At the highest point of its path projectile explodes and breaks up into $2$ fragments of ...
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0answers
45 views

How is momentum conserved in this electromagnetic scattering?

It is well known that verifying momentum and energy conservation in the presence of electromagnetic fields requires care as the fields themselves carry energy and momentum (see Griffiths chapter 8 for ...
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2answers
42 views

Ball collides with another. Find velocities [closed]

A ball moving at a velocity of 5.0 m/s east when it collided with an identical ball at rest. Both balls are the same mass. The first ball moved at 60 degrees north of east. The second went 30 ...
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83 views

Momentum and position for free particle

In the section of 'The free particle' in 'Introduction to quantum mechanics, second edition' by Griffiths page 65. He has the wave equation as $$\Psi(x,t) = \frac{1}{\sqrt{2 \pi}} ...
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42 views

Momentum when a people fall down to ground (Related to momentum, gravity, lever)

According to the Newton's laws, free fall is subjected to the pull of gravity at acceleration of 9.8 m/s per second. (Something like this) But I don't think the principle of "free fall" is applicable ...
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3answers
75 views

Can a submarine be powered by a wind turbine?

This is not intended as a realistic way for propulsion of submarines, it is just an interesting thought experiment. Say I want to travel directly towards the wind, only powered by the wind. This is ...
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61 views

How could a heavy manhole cover jump out of the ground, fly through the windshield and hit a driver in a car?

Today (12 of Feb), there was this accident in Boston where a driver was killed because a manhole cover (~200lbs) had somehow become airborne and struck her. The car looks like an SUV, so her head must ...
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37 views

Two Dimensional Momentum [closed]

[2] []3> A tennis player receives a ball of mass $60\ \mathrm g$ travelling horizontally at $55\ \mathrm{ms}^{-1}$ perpendicular to the net, and returns it at $28\ \mathrm{ms}^{-1}$ in a direction at ...
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63 views

How does commutation between the hamiltonian and angular momentum operator (squared) imply conservation of Angular momentum?

So we are looking at central potentials in QM; The lecturer poses the question, when is $\textbf{L}$ conserved? He then considers the commutator of $\hat{H}$ and $\hat{L^2}$. We have; ...
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32 views

Assumptions in two balls falling experiment

A typical undergraduate physics class problem to demonstrate the effects of conservation of momentum is to have two balls of different mass falling one above the other (the largest mass below) to the ...
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1answer
77 views

What is the origin of the quantum operators for $p$ and $E$? [closed]

It is always stated the quantum operators for p and E are the ones we´re familiar with (the operator for energy, $H=i\hbar\frac{\partial}{\partial t}$ and the momentum operator, ...
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40 views

Proving Probability Current and Momentum relationship

I am trying to show that $\mathbf j = \frac{\hbar}{2mi}\left(\Psi^* \mathbf \nabla \Psi - \Psi \mathbf \nabla \Psi^{*} \right) \,, $ simplifies to $\mathbf j = \frac{\mathbf p}{2m} (|\Psi|^2) $. I ...
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1answer
56 views

Path of a swinging object on a rope [closed]

With my lanyard in hand (weighted by my keys), a gentle swinging motion will put the keys in pendulum motion, swinging back and forth. Pendulum motion is relatively easy to model since it is ...
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3answers
169 views

Momentum operator representation

If $\hat{p}$ acts on position eigenstate, it is $$\tag{1}\hat{p}\left|x\right\rangle=+i\hbar\frac{\partial }{\partial x}\left|x\right\rangle .$$ But in general $$\tag{2}\hat{p} = -i\hbar ...
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53 views

What is relationship between linear and angular momentum?

I'm confused about imparting momentum to a sphere, which causes it to rotate without slipping. Does the momentum applied go: only to the rotational motion and the linear is a consequence of the ...
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1answer
54 views

What makes cart with a moving object in it gain speed (no friction anywhere)?

I would like to understand what makes the cart below the moving object move. There is no friction between any of the objects. The cart is moving therefore there is force applied to it. The only force ...
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36 views

The physics of an anvil [closed]

I am trying to understand how an anvil might best be made. An anvil requires two essential characteristics: enough hardness to not be deformed under the blows of the hammer, but as little rebound and ...
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2answers
116 views

Conservation of momentum and conservation of energy

I had the impression that conservation of momentum is valid only when we consider no loss of kinetic energy into heat etc. My tutor says that even if we have loss of kinetic energy as heat in a ...
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3answers
258 views

How can I solve this quantum mechanical “paradox”?

Let a (free) particle move in $[0,a]$ with cyclic boundary condition $\psi(0)=\psi(a)$. The solution of the Schrödinger-equation can be put in the form of a plane wave. In this state the standard ...
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1answer
72 views

Particle sliding down frictionless hemisphere on frictionless surface

http://web.physics.harvard.edu/uploads/files/undergrad/probweek/prob87.pdf http://web.physics.harvard.edu/uploads/files/undergrad/probweek/sol87.pdf The problem and the suggested solution are in the ...
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1answer
51 views

Calculating post-collision velocity [closed]

Consider two persons $p1$ and $p2$ of the same mass , such that they are together moving rightward with a velocity of $v/2$ Now person $p1$ pushes $p2$ in the left direction. According to newton's ...
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30 views

Does inelastic collision mean the colliding particles have to necessarily stick?

In a case when particle 1 is moving vertically upwards and particle 2 if moving horizontally and they collide perfectly inelastically, why would the particles stick ? Since inelastic collision means ...
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2answers
71 views

When a ball bounces on a wall at an angle, why does the angle of incidence equal angle of reflection?

When a ball is thrown to a wall without spin and bounces, supposing it's an elastic collision, why does the angle of incidence equal the angle "reflection" (relatively to the normal), why isn't it any ...
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1answer
46 views

What causes the skidding of the wheels of a moving car? Momentum or inertia?

In a moving car, when brakes are applied suddenly the wheels skid.I have these two explanations in my mind and both seems correct to me.1. The momentum of the car must be conserved so the car ...
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2answers
59 views

Why do $\hat{X}$ and $\hat{P}$ have to correspond to position and momentum?

As far as I understand, in QM we treat observables as operators, and the eigenvalues of these operators are the possible values we can measure of the observables. It is usually simpler to work in the ...
2
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1answer
62 views

Nail clippers and conservation of momentum

As I clip my fingernails using nail clippers, pieces of nails sometimes fly off violently, reaching the other end of the room. What's happening in terms of conservation of momentum, how are the pieces ...
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1answer
91 views

conservation of momentum? [closed]

At hyperphysics I got this image, with the same description in text as is in this image It says that when a massive particle (say $A$) moving with a velocity collides with an object having a ...
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1answer
62 views

Is $E = p^0$ in non-inertial frames?

In special relativity the energy of a particle is the 0-component of the 4-momentum. However, is this still true in non-inertial frames, and in particular in non-freely-falling frames in general ...
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50 views

Why the speed of a cart stays the same, on a frictionless surface, as the sand falls out? [closed]

This is a question on my test. I got it right by guessing. Can someone explain it, in terms of equations of momentum. I first thought of the equation of conservation of momentum: ...
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1answer
95 views

Mathematical proof of an electron cant absorb a photon [duplicate]

How can we mathematically prove that a free electron cant absorb a photon totally?