The conservation-laws tag has no wiki summary.
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1answer
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Scattering problem: Converting the two-body lab frame problem into a one-body center-of-mass frame problem
I'm reading the section on scattering in Goldstein's Classical Mechanics, and I have a rather basic question about this.
It says that scattering in the laboratory is a two-body problem because of ...
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2answers
173 views
The time component is $\gamma m c$, so shouldn't $E=mc$?
Basically, the book is Brian Cox's Why Does $E=mc^2$?: (And Why Should We Care?).
I just finished Chapter 5, where we derived the spacetime momentum vector (energy-momentum four vector, as he ...
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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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2answers
258 views
How can a non-conservative field be a scalar multiple of a conservative field?
Okay so I was reading this from University Physics by Freeman and Young and on the topic of inductors as circuit element, they wrote that $\mathbf{E_c} + \mathbf{E_n} = 0$ which makes no sense to me
...
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1answer
345 views
What causes a force field to be “nonconservative?”
A conservative force field is one in which all that matters is that a particle goes from point A to point B. The time (or otherwise) path involved makes no difference.
Most force fields in physics ...
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1answer
165 views
How to determine n equidistant vectors from point P in three dimensions
As an assignment for uni I need to figure out an algorithm that explodes a particle of mass $m$, velocity $v$, into $n$ pieces.
For the first part of the assignment, the particle has mass $m$, ...
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1answer
90 views
Can 3 photons be combined to give a spin-0 projection?
Motivation: The neutral pion decays to 2 photons ($\pi^0\to\gamma\gamma$) most of the time. For the decay of the neutral to 3 photons ($\pi^0\to 3\gamma$) we have an upper limit on the branching ...
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1answer
70 views
Shooting a bullet at a system of blocks [closed]
So, I made this question up myself.... and I'm curious about the answer. It requires only secondary-school-level knowledge of physics:
You have a surface (ground) with a certain coefficient of ...
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0answers
42 views
Conservation laws in mSUGRA model
Can somebody list all the quantum numbers (beside R-parity) that are conserved in vertex for SUSY particles in mSUGRA model?
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1answer
108 views
Entanglement and conservation
Is the following assertion sufficiently unique to merit a paper? Every absolute conservation law implies a corresponding form of entanglement, not just spin (angular momentum). Linear momentum ...
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0answers
126 views
Does electron go through a forbidden state when annihilate with positron?
Let's consider an electron-positron pair with total spin equal to zero. When it annihilates it can not emit only one photon because it would have zero momentum and nonzero energy. The pair emits two ...
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0answers
557 views
Do symmetries increase the number of conserved quantities? [closed]
Let us consider a classical mechanical system of N particles in a constant external field. We have 3N coordinates and 3N velocities, so totally 6N unknown variables. We have 6N ordinary differential ...
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5answers
173 views
Why is momentum conserved (or rather what makes an object carry on moving infinitely)?
I know this is an incredibly simple question, but I am trying to find a very simple explanation to this other than the simple logic that energy is conserved when two items impact and bounce off each ...
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1answer
144 views
What happens if object is thrown in empty space?
If I throw a object in empty space, I apply a force to throw that.
Then it gains some acceleration and it's speed increases.
So will it's speed keep on increasing, or it will get stable?
If yes, ...
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3answers
371 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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1answer
141 views
M1 vs M2 on a frictionless surface
I was wondering, if I had a frictionless surface and I had an M1 that was 100kg and an M2 that was 1kg and I pushed each separately with an equal force F would they move at the same speed or am I ...
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3answers
650 views
Conservation of electric charge in Feynman diagram
Here is a Feynman diagram showing the mutual annihilation of a bound state electron positron pair into two photons:
Is the electric charge conserved at the point A (or B)? What is the "charge" of ...
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2answers
65 views
Conservation of Momentum from Recoil Speed
A gun has a recoil speed of 2 m/s when firing. If the gun has a mass of 2kg and the bullet has a mass of 10g (0.01 kg) what speed does the bullet come out at?
The gun has zero total momentum before ...
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2answers
426 views
Calculating force of impact
Since $\text{force = mass}\times\text{acceleration}$,
is it right to say that an object traveling at a high
constant velocity (zero acceleration), exerts zero
force upon impact with a stationary ...
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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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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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1answer
86 views
Period of an Object in Periodic Motion
My attempt (if it matters):
The initial period is given by $T_X = \frac{2\pi X}{v}$ for some $v$.
The new period is given by $T_Y = \frac{2\pi Y}{v}$ for the same $v$.
$Y = \frac{X}{2}$, so ...
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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
195 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
172 views
What process could produce two neutral pions only?
Any examples?
$$? \rightarrow \pi^0 \pi^0$$
If such a process exist, could there be nonzero total orbital angular momentum in the final states of the two neutral pions? But then how to understand ...
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1answer
216 views
How did one get the defining equation of probability current and conservation of probability current and density?
I'm reading the Wikipedia page for the Dirac equation:
$$\rho=\phi^*\phi$$
and this density is convected according to the probability current
vector
$$J = ...
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1answer
137 views
Charge-less, Mass-less, Spin Fields
after looking through a couple QFT texts it seems that all the spin-1/2 fields come associated with a charge of some sort. I was wondering if it's possible to write down a classical lagrangian (with ...
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2answers
118 views
What is the origin of nonconservative force?
My understanding about conservative force is a force that its work is independent of path such that we can construct another form of the work called potential to make our life easier.
For friction, ...
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2answers
144 views
Perpendicular Elastic Collision (different masses, different velocities)
I'm stuck on a mechanics problem and I can't make any headway past momentum and kinetic energy being conserved. Here is the problem:
Two hover cars are approaching an intersection from ...
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0answers
53 views
Conservation of angular momentum tensor $L^{\mu\nu}$ in special relativity [duplicate]
I have edited this question because I don't think that the related post answers my question fully. It refers to Noether's theorem but I would like an explicit illustration in an easier fashion: The ...
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1answer
161 views
Calculating a 2D collision between two perfectly circular disks
Assume I have two disks, $p_1$ and $p_2$, of radius $r$, with their own velocities (preferably in $(x,y)$ form, but $(m, \theta)$ works too) and masses (unit-less, but same unit) collide in two ...
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1answer
79 views
Combining Conservation Laws ~ Homework Problem Guidance
Problem 8.79 - Combining Conservation Laws
A 5.00-kg chunk of ice is sliding at 12.0 m/s on the floor of an ice-covered valley when it collides with and sticks to another 5.00-kg chunk of ice that is ...
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1answer
273 views
Kinetic energy in the center of mass
In a collision of a particle
of mass $m_1$ moving with speed $v_1$ with a stationary particle
of mass $m_2$ not all the original kinetic energy can be converted
into heat or internal energy. what ...
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3answers
238 views
Interaction between a Pair of Particles
We consider a particle, A receiving energy from a second one,particle B in a one dimensional collision.
$$E^2=p^2+m_0^2$$
$$EdE=pdp$$
For particle A:
$$E_AdE_A=p_Adp_A{\;\;\;\;\;\;}(1)$$
For ...
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1answer
180 views
Scattering problem: Finding the speed of the scatterer after collision
A particle of mass $M$ moving in a straight line with speed $v$ collides with a stationary particle of the same mass. In the center of mass coordinate system, the first particle is deflected by 90 ...
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2answers
182 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), ...
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189 views
Am I doing this conservation of angular momentum problem correctly? [closed]
I am doing some calculations for a practical project of mine. Basically I have a levitating sphere with gravity countered and close to 0 friction when the sphere rotates(due to airdrag). Inside the ...
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3answers
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Classical mechanics and the speed of a train-mosquito collision, when perfectly rigid bodies
This is all under the assumption that they are perfectly rigid bodies:
A train is moving at 300m/s.
A mosquito is moving directly towards it, head-on, at 4m/s.
When the mosquito and the train ...
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1answer
734 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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2answers
225 views
Newton's Third Law - Action and Reaction on space, what happen with the astronaut? [closed]
This is a question from my homework.
Imagine an astronaut doing a repair in his ship, "parked" somewhere in space where gravity result is zero. As he can not do the repair, gets nervous and throws ...
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1answer
104 views
Could a people do all sort of gymnastics movement in vacuum space? [closed]
Could a people do all sort of gymnastics movement in vacuum space? I asked this because I am worry about that the astronaut leave the space shuttle during emergency could not go back to earth by ...
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1answer
383 views
Question on Impulse-Momentum theory
A 5kg stone kicked by a student undergoes a velocity change from 6m/s
to 10m/s in 4 seconds;
---- What is the momentum change of the stone within the time interval?
---- What impulse ...
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3answers
280 views
Is the continuous transformation of energy from one form to another one free? Or it consumes some quantity of who knows what?
Sorry for the unclarity. I probably created some bias in your mind having tagged my question with energy-conservation and conservation-laws.
I simply consider that, relatively independently of ...
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1answer
135 views
Mathematical question on Collisions [closed]
A 2.5kg ball travelling with a speed of 7.5m/s makes an elastic
collision with another ball of ...
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votes
1answer
182 views
Tricky Conservation of Momentum problem: find the ratio of the carts by mass percentage lost [closed]
A wagon is coasting at a speed $v_A$ along a straight and level road. When 42.5% of the wagon's mass is thrown off the wagon, parallel to the ground and in the forward direction, the wagon is brought ...
