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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306 views
Momentum as Generator of Translations
I understand from some studies in mathematics, that the generator of translations is given by the operator $\frac{d}{dx}$.
Similarly, I know from quantum mechanics that the momentum operator is ...
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1answer
99 views
Integration of constant: $\int dp = \Delta p$ in impulse formula
In University Physics, it has something like:
$$\int \sum F dt = \int \frac{dp}{dt} dt = \int dp = \underbrace{p_2 - p_1}_{\Delta p?}$$
But I thought $\int dp = p$? Though my maths is really rusty ...
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0answers
26 views
Elastic Collision Between Two Objects [duplicate]
Possible Duplicate:
Elastic Collision And Momentum
I've already asked this question, Elastic Collision And Momentum, but I didn't find the answer particularly helpful--sorry, I don't mean ...
5
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2answers
235 views
Photon energy - momentum in matter
$E = h\nu$ and $P = h\nu/c$ in vacuum.
If a photon enters water, it's frequency $\nu$ doesn't change.
What are its energy and momentum : $h\nu$ ? and $h\nu/c$ ?
Since part of it's energy and momentum ...
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1answer
114 views
Analysis of the impulse of 2 colliding carts under the effect of magnetic repulsion
Hi there! I have a question about an experiment that was conducted. It is related to momentum.
2 carts were put on a track on opposite sides. They were then propelled towards one another at ...
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1answer
61 views
Physics Impulse
This is the problem I am dealing with:
"One of the functions of an automotive air bag is that it lengthens the collision time. Without an air bag, suppose the 100Ns impulse of a collision is taken up ...
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1answer
152 views
Momentum And A Car Collision
I am studying an example problem, concerning the very topic mentioned in the title. In this example problem, a car has a head-on collision with the wall; the initial and final velocity are known, as ...
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1answer
65 views
A Decrease In Momentum?
The specifics of a question I am working on are, "After a 0.280-kg rubber ball is dropped from a height of 1.80 m, it bounces off a concrete floor and rebounds to a height of 1.45 m."
Why doesn't the ...
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1answer
123 views
Momentum And Energy Problem
The information to the question is, "A $59.0~kg$ boy and his $38.0~kg$ sister, both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backward with a velocity ...
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1answer
332 views
Relative Velocity and Momentum
The question is, "A $45.5~kg$ girl is standing on a $140~kg$ plank. Both originally at rest on a frozen lake that constitutes a friction-less, flat surface. The girl begins to walk along the plank at ...
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votes
4answers
556 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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1answer
197 views
What is the linear momentum of an inelastic and elastic collision?
The arrows in the figure represent the linear momentum of two balls before they collide. If the collision is perfectly inelastic, find the linear momentum after the collision. If the collision is ...
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1answer
96 views
Conservation of momentum with MOND
Assuming as true the phenomenological MOND law for low accelerations ($< 10^{-10} m s^{-2} = a_0$), and considering a small mass $m$ attached to a larger mass $M$ by a faint spring (let's think of ...
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0answers
43 views
What is the momentum of the system in the center of mass frame? [closed]
During a baseball game, a batter approaches the plate. The pitcher hurtles the ball in the direction of the batter at a speed of 85 miles per hour. The batter swings and makes contact with the ball. ...
0
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1answer
101 views
Non-relativistic Kepler orbits
Consider the Newtonian gravitational potential at a distance of Sun:
$$\varphi \left ( r \right )~=~-\frac{GM}{r}.$$
I write the classical Lagrangian in spherical coordinates for a planet with mass ...
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1answer
740 views
Violation of Newton's 3rd law and momentum conservation
Why and when does newtons 3rd law violate in relativistic mechanics? Check this link http://www.animations.physics.unsw.edu.au/jw/Newton.htm.
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6answers
1k views
How can there be net linear momentum in a static electromagnetic field (not propagating)?
I understand from basic conservation of energy and momentum considerations, it is clear in classical electrodynamics that the fields should be able to have energy and momentum. This leads to the usual ...
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2answers
154 views
Conservation of Linear Momentum with respect to a given direction
Is linear momentum conserved in any direction? More specifically, if you project all momentum vectors in a system onto another vector, will momentum be conserved?
I know that momentum is conserved ...
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2answers
965 views
Inelastic collision and conservation of linear and angular momentum
Is it possible for two spheres (a & b) to have an inelastic collision with BOTH the total linear and angular momentum preserved? I'm doing some physics simulation of some spheres attracting each ...
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1answer
224 views
Controlling the outcome of a quantum measurement through translational entanglement
According to the paper:
A. S. Parkins and H. J. Kimble, Phys. Rev. A 61, 52104 (2000).
http://pra.aps.org/abstract/PRA/v61/i5/e052104
You can entangle position and momenta of two atoms by using ...
2
votes
2answers
3k views
Difference between momentum and kinetic energy
From a mathematical point of view it seems to be clear what's the difference between momentum and $mv$ and kinetic energy $\frac{1}{2} m v^2$. Now my problem is the following: Suppose you want to ...
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1answer
157 views
Intuition of Impulse Formula $J = \sum F \Delta t$
I understand that
$$\begin{align}
J = \sum F \Delta t &= \Delta p \\
\sum F &= \frac{\Delta p}{\Delta t} \\
&= \frac{mv_2 - mv_1}{\Delta t} \\
&= m \cdot \frac{\Delta v}{\Delta t} \\
...
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3answers
268 views
Same momentum, different mass
The question is: if
A bowling ball and ping pong ball
are moving at same momentum
and you exert same force to stop each one
which will take a longer time? or some?
which will have a longer ...
0
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2answers
217 views
Center of mass of a car
This might be little of the track but my question is more on possibility of application of principle of center of mass.
The probability of a vehicle overturning depends more on the level of center of ...
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votes
3answers
393 views
Newton's 3rd Law: How can I break things?
If I punch a wooden board hard enough and it breaks in two, has the board still exerted a force of equal magnitude on my fist?
When the board breaks in two due to my force, the halves have a ...
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1answer
90 views
Would synchronized dancing be a good way to describe entangled atoms to a laymen?
I was talking my professor about entanglement swapping between light and matter and it is briefly described here:
You start out with a crystal capable of doing parametric down conversion of incoming ...
3
votes
3answers
251 views
Conservation of Energy in Different Frames of Reference
Say I have a bucket of fuel that can produce 150J of energy by combustion. No matter what frame of reference an observer or the bucket of fuel is in, since the configuration of molecules stay the ...
2
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1answer
123 views
Total momentum of the Universe
What is the total momentum of the whole Universe in reference to the point in space where the Big Bang took place?
According to my reasoning (and a bit elementary knowledge) it should be exactly ...
3
votes
1answer
481 views
Conservation of linear and angular momentum
Suppose I have two rigid bodies A and B and they are connected by a spring which is attached off-center (thus possibly causing torques). Due to the spring a force $f$ acts on A and a force $-f$ acts ...
2
votes
3answers
202 views
Explanation for classic mechanics puzzle
I'm trying to figure out a nice way to describe to a kid the physics behind these experiments:
Assuming ideal conditions, we have a small boat with a sale, close to a lake's shore and a fan fixed on ...
12
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4answers
577 views
Energy is actually the momentum in the direction of time?
By comparatively examining the operators
a student concludes that `Energy is actually the momentum in the direction of time.' Is this student right? Could he be wrong?
5
votes
4answers
6k views
Is pushing actually easier than pulling?
It is generally assumed that pushing a cart is more easier than pulling one. But why?
Is there any difference in terms of force required to achieve the same amount of displacement?
Or is it just a ...
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2answers
155 views
Having Trouble With The Principle Of Conservation Of Momentum For a Multiparticle System
I'am reading John Taylor's Classical Mechanics chapter 1 page 20 where he proves the principle of conservation of momentum which states "If the net external force $F^{ext}$ on an $N$-particle system ...
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2answers
161 views
Derivative of a Position Eigenket
I was flicking through Zettili's book on quantum mechanics and came across a 'derivation' of the momentum operator in the position representation on page 126. The author derived that ...
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0answers
822 views
Moment of Inertia problem [closed]
I'm revising for my exam and there's this one problem where I can't get the correct answer, so I'd like to know how to solve it. The problem is:
Two boys, each with a mass of 30kg, are sitting ...
2
votes
1answer
120 views
Mass Shell in Light Cone Coordinates
I'm reading Zweibach's introduction to string theory, and don't understand one of his claims.
He defined the mass shell to be the set of points in momentum space s.t. $p^2+m^2 = 0$. Then the physical ...
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3answers
150 views
The impossible possibility - weightless mass
I have a rather theoretical question about inertia.
Let's say I have an object that weighs a ton (2,000 lbs.), and is sitting in my front yard, for instance. If it would suddenly become immune to ...
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1answer
294 views
Momentum in quantum mechanics
In quantum mechanics, we can have some superposition of matter waves that have different wavelengths. If then, can't momentum of a particle change every time measurement takes place? Or should I ...
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1answer
90 views
Cyclic co-ordinates implying the constant velocity motion of center of mass of a system of particles
I'm reading the section on Central Force in my textbook (Goldstein's Classical Mechanics has a similar argument in the chapter titled "The Central Force Problem", first section), where we have the ...
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1answer
209 views
Can a fly pierce itself onto a cactus needle?
Somebody on reddit posted a ridiculous picture today of a fly pierced onto a needle of a cactus: http://www.reddit.com/r/pics/comments/xarue/what_are_the_odds_of_this_accident/
Whilst the OP claims ...
2
votes
3answers
197 views
Should any theory of physics respect the principle of conservation of angular momentum or linear momentum?
Is it possible that a theory that can describe the universe at the planck scale can violate things that we now consider fundamental in nature?For example can it violate rotational and translational ...
1
vote
2answers
53 views
Can you launch an item farther by slamming into it or accelerating it along a length
I am trying to desgin a little penny balista toy (built with a 3d printer).
The short description is that there is a track with a mass ("hammer") that slides along it. There is a stack of pennies in ...
0
votes
2answers
94 views
Really basic mechanics and Galilean Relativity question
Consider two solid objects: A and B.
System 1:
A <----- B
10m/s
System 2:
A -----> B
10m/s
...
0
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0answers
248 views
Error Analysis, Change in momentum, Kinetic Energy
If momentum of an object is increased by 10%,then its kinetic energy will be increased by?
Well, I don't need the solution logically by calculating the change in Kinetic Energy etc, but my question ...
0
votes
0answers
34 views
Does the direction of a rocket relative to an orbiting mass reduce the orbiting mass' orbital velocity?
Does a rocket taking off in the same direction of an orbiting mass (asteroid to planetary size) reduce the mass' orbital velocity versus the same rocket taking off in the opposite direction of the ...
4
votes
3answers
499 views
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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3answers
374 views
Will a stone thrown in space move forever?
If I throw a stone on space, in a place where gravity is equal zero, will the stone move forward forever, because no air, so no friction?
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vote
3answers
541 views
what is physical meaning of this partial derivative?
what is physical meaning of this partial derivative:
$$\frac {\partial p_x}{\partial x}$$
i know how do i solve it when the case is just derivative but partial derivative is a bit Hectic!.
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1answer
688 views
Spring compression and Momentum
I am asked to rate a series of elastic collisions in order of greatest time of max compression to least time of max compression for several vehicles with varying masses and velocities, which strike a ...
0
votes
2answers
183 views
Conservation of momentum equation, how do I factor out v0Final and v1Final?
I am trying to figure out an equation for conservation of momentum. So,
If combined momentum before and after the collision is the same, and momentum is velocity times mass, then for 2 objects (A,B), ...
