Conservation laws Definition and 114 Threads

Hi, In general relativity we have no general conservation of energy and momentum. But if there exists a Killing-field we can show that this leads to a symmetry in spacetime and so to a conserved quantity. Thats what the mathematic tells us. But I don't understand what's the meaning of an...

Does the relativity of simultaneity imply the impossibility of non local conservation laws?

I am confused about the current physics regarding neutrinos and implications about the conservation laws of mass-energy and linear momentum. I have read the threads listed for similar discussions, including, "How does conservation of energy/mass apply to neutrinos?", and none of them seem to...

What ensures conservation of energy and conservation of momentum in Electron-Positron annihilation? If e=mc2 and momentum = mass*velocity, couldn't the energy equivalence of the electron and the positron be converted to make one photon, or more that 2 photons? I've read that two photons are...

Homework Statement Question: Figure 1: QUESTION ABOVE. Homework Equations The Attempt at a Solution :[/B] P + P → K+ + K- + P + P Firstly, I just wanted to check that this is correct. I found the answer pretty quickly by googling it but have since spent a long while trying to understand...

Hi Guys, I was wondering; if electronic charge is conserved by Kirchoff's Current Law, then does this mean that the total number of electrons traversing any given circuit at any time is constant?

Homework Statement A billiard ball of mass M is initially at rest on a horizontal frictionless table. Another ball of mass m < M and velocity ##\vec{v}## in the positive x-direction hits the first ball in a pefectly elastic collision. After the collision, the balls move with (unknown)...

Hello, this thought I'm having might be difficult to explain, but i will do my best. Ever since i learned about conservation of energy, conservation of mass (or mass plus energy due to E=mc^2) and conservation of linear/angular momentum, i always found it weird that things in nature can...

Homework Statement 15. A solid sphere of mass 6.0 kg is mounted on a vertical axis and can rotate freely without friction. A massless cord is wrapped around the middle of the sphere and passes over a 1.0 kg pulley and is attached to block of mass 4.0 kg, as shown. What is the speed of the...

Homework Statement Homework Equations v = wr K_total = 1/2Mv^2 + 1/2Iw^2 L = Iw p = mv The Attempt at a Solution a. No friction or other outside forces are acting on the system, so linear momentum is conserved. The collision is elastic, so kinetic energy is conserved. There...

Hi, Assume we have a source that emits several copies of the same quantum state which is a superposition of several eigenstates of the Hamilton operator with different energies. We can calculate the expectation value of the energy of this state and therefore also the energy the source...

I was arguing today with a friend and the argument seemed pretty pointless because we had nothing to back up our facts with, so I thought about hearing your opinion(s). Do black holes violate laws such as the conservation of matter + conservation of energy? I'm currently leaning towards 'yes'...

2) A π0 of kinetic energy 350 MeV decays in flight into 2 γ rays of equal energies. Determine the angles of the γ rays from the incident π0 direction. Not sure where I am going wrong but my answer is not correct. Energy of π0 meson E = 350 MeV Rest mass Energy of π0 meson E0 = 135...

Doesn't traditional time travel violate conservation laws? If I could in effect materialize in the past, then the universe, being an isolated system would have suddenly gained matter/energy out of nowhere! Also, the atoms that make up my body would then be in two places at once since they...

Hello, I am hoping for some input concerning shall we say the philosophy of mechanics, particularly with relation to the concept of force. Most textbooks treat force as being something of a primary concept. A fundamental aspect of nature much like energy and mass and therefore something...

As we are being introduced to this new lesson, it gets difficult sometimes to indicate which component of either (linear or angular momentum) is conserved. Is there a strict rule to help me indicate which is which? Hmm, if not, can you give me the logical way through it? Thanks in advance...

Homework Statement A 15kg block is attached to a very light horizontal spring of force constant 500 N/m and is resting on a frictionless horizontal table. It is struck by a 3kg stone traveling horizontally at 8m/s to the right, whereupon the stone rebounds at 2 m/s horizontally to the left...

Homework Statement A small wooden block, of mass M, lies in the middle of a horizontal table of length L and height h above the floor. The coefficient of kinetic friction between this block and the surface of the table is μ. A bullet, of mass m, is shot with a horizontal velocity into...

Hello PF community! I'm having trouble with what strikes me as an inconsistency within conservation of energy, conservation of momentum, and the four-momentum invariant equation (E2-p2c2 = m2c4). For the sake of this question, I'll be using non-relativistic mass--i.e. mass is the same in all...

Conservation Laws - Finding angle ? Homework Statement Having trouble with question 2, a) - See below Homework Equations The Attempt at a Solution Which conservations laws am I suppoe to use to figure this out? THanks!

In "The Algebra of Grand Unified Theories" http://arxiv.org/abs/0904.1556" john Baez (see page nb 9) shows how the conservation of eigenvalues (T3 isospin) appears if there is an intertwiner between the representation spaces of the symmetry group. I discovered intertwiners for the first time...

It seems to me that there is a difference between, say, the law of conservation of linear momentum or energy and the law of conservation of angular momentum. The first two are valid in any frame of reference and their invariance is a direct consequence of the relativity principle, whereas...

A while back I piggy-backed onto another thread (and then withdrew it as being out of place) an example of a system possibly violating the conservation of energy and momentum (angular momentum directly) - a spinning hollow right circular cylinder placed under frictionless axial compression. Many...

Hi How many conservation laws are there ? 1. Conservation of energy 2. " " momentum 3. " mass 4. " charge ? TIA

It's been 20 years since I took field theory in grad school, and I didn't really understand it all that well even then, so I'm basically looking for a very low-level explanation of the following issue... In the sum-over-histories approach, there is the question of which histories to include...

We all know that the universe is expanding and for that matter accelerating. Science is now starting to realize that the universe will expand forever and the big crunch will never occur due to recent data of a supernova. My point to all this is, quantum theory states that a vacuum must always...

Hey, It seems like this is impossible because momentum conservation is violated. I had a Q where an electron underwent an energy transition and emitted a photon, and then they asked whether it was possible for the photon to be reabsorbed by the electron to undergo the same transition as...

Hello, everybody! During the whole of my undergraduate study of physics, this one thing always bothered me. It concerns the interplay of conserved quantities, symmetries, Noether's theorem and initial conditions. For a system of N degrees of freedom, governed by the usual Newton's laws...

I've been trying to organize my thoughts about conservation laws in GR, and so far I'm not having as much success as I'd like in bringing order to the whole topic. Maybe this is just the way GR is -- conservation laws don't play their usual central role, and their behavior varies on a...

Is my understanding correct: Charge is conserved at a vertex. So the charges of particles pointing in towards a vertex and the charges of particles pointing out must be equal. Alternatively: The sum of the charges at a vertex must be zero. So if this is correct, can someone explain the...

I am working on a homework assignment for my particle physics class, and it requires I understand what forces conserve what quantum numbers. As I understand it: Strong Conserves Isospin, I3 projection, s, c, b, t, Baryon number, lepton flavor E&M Conserves I3 projection, s, c, b...

Not a homework question, but I am trying to understand some stuff in Leibniz's 17th century "natural philosophy" which got me realizing that I don't have a clear grasp of my high school physics from 40 years ago. Imagine a closed system consisting of 2 objects, and imagine a perfect elastic...

Is conservation laws are more fundamental than Newton's second law in Newtonian mechanics? I know from the point of view of Noether's theorem conservation laws are more fundamental. But all the conservation laws can be derived from the F= ma equation. And from these conservation laws I can't...

Last time people concluded that 'I proved the law of conservation of energy and momentum wrong by my invention'...but the reality is strictly opposite. If this invention DOES NOT work THEN then 2 laws are wrong. This invention follows all rules and regulation governed by the physics book...

Perpetual motion idea: Sit on a bench with a collimated laser, single slit and detector screen. This prepares particles with identical and symmetric spatial wave-functions, so each measurement transfers an independent, random quantity of transverse momentum (from a symmetric distribution) to...

Homework Statement A 0.2 kg disc slides down from smooth track of height 1.8m. It arrives at a rough 1 kg block resting on a smooth surface. The friction between them is 1.2N. Find the distance traveled by the disc on the block before it comes to rest relative to the block. Homework...

Hi all, This is my first post, so please forgive me if this has already been discussed. There is a question that has perplexed me for years, and I am hoping someone at this forum can shed light or point me in the right direction. If two like charges separated by a distance, d, quickly and...

I'm doing some research into time travel for a presentation I have to give in a month or so, and I'm currently looking at the compatibility of Time Travel and the Laws of Conservation. Sending an object back in time would increase the mass - and hence the energy - in the Universe at this...

Do resistors in series and parallel obey conservation laws? why? I think yes, because I add individual resistance for the effective resistance ... but why? :| what's a true and deeper explanation for this??

Homework Statement Consider a small body of mass m placed over a larger body of mass M whose surface is horizontal near the smaller mass and gradually curves to become vertical at height h. The smaller mass is pushed on the longer one at speed v and the system is left to itself...

A 4.00 kg steel ball strikes a wall with a speed of 9 m/s at an angle of 60.0° with the surface. It bounces off with the same speed and angle (Fig. P8.9) If the ball is in contact with the wall for 0.200 s, what is the average force exerted on the ball by the wall? F\DeltaT = \Deltap p =...

I just got a copy of Feynman's lectures on Physics the other week. They are very interesting. Near the end of the 4th chapter, he begins discussing conservation laws. One of the laws he gives is the conservation of baryons. I noticed early in the first volume, the lectures were published in...

In classical mechanics (also in QM I guess), the fundamental laws of conservation (energy, momentum and angular momentum. tell me if I forget something) are valid only if the system is closed and the net external force is zero. WE define what the system is. We can include or exclude things...

Place equal amounts of matter and anitmatter in a box on a scale. It's a very good box; it's very reflective, and light doesn't get in or out. Allow all the stuff to annihilate to photons. The box floats away. Has a conservation law been violated?

Homework Statement A uniform solid sphere, with diameter 28 cm and mass 2.5 kg, rolls without slipping on a horizontal surface, at constant speed of 2.0 m/s. 1) What is the rotational kinetic energy? 2) What is its total kinetic energy? 3) What is its angular momentum? Homework...

Homework Statement A cannon in a fort overlooking the ocean fires a shell of mass M at an elevation angle, theta and muzzle velocity, v0. At the highest point, the shell explodes into two fragments (masses m1 + m2 = M), with an additional energy E, traveling in the original horizontal...

Hi, i just need to get together all the conservations/violations that the weak interaction conserves/violates. I know about parity, charge conjugation and basic properties such as charge and lepton number but i was wandering if anybody could think of any more. No mathematics please! Thanks.

In the time evolution defined by the Shrodinger's equation, the expectation value of the energy is conserved. However, in a collapse of the state, where state vector gets projected onto some subspace of physical states, the expectation value is not conserved. Does this mean that through...

The Reynolds Transport theorem (RTT) is usually applied to derive the conservation of mass, momentum and energy in a fluid. But when I try to apply the RTT to other physical quantities, I get weird results. Can anyone see where I'm going wrong? As a simple example, take the physical...

Homework Statement Two balls go vis-a-vis (each of them speed is v) and strike. Hit is absolutely elastic. After the hit, one of the balls changes his motion direction 30 degrees. I need to find the direction of the other ball and both ball speeds after the hit. The Attempt at a Solution...