# How many conservation laws ?

by bksree
Tags: conservation, laws
 P: 55 Hi How many conservation laws are there ? 1. Conservation of energy 2. " " momentum 3. " mass 4. " charge ???? TIA
 P: 748 energy momentum angular momentum charge gravity + others I can't think of right now mass conservation isn't really true
 HW Helper P: 6,164 color charge weak isospin probability density CPT symmetry (combining charge, parity and time conjugation) Lorentz symmetry (ripped from http://en.wikipedia.org/wiki/Conservation_law)
PF Patron
P: 10,403

## How many conservation laws ?

 Quote by Curl mass conservation isn't really true
Yeah, It all depends on what you mean by "mass". Converting electrons-positrons to gamma rays removes the "mass" and turns it into energy or momentum or whatever.
 Mentor P: 14,660 I don't know what "conservation of gravity" even means. As for weak isospin, it is certainly not conserved, although it's third component is. There is no answer to this question. What is conserved and what is not depends on the state you are looking at: an object in a central force orbit always has angular momentum conserved, but in a 1/r potential, it also has another quantity conserved: the Runge-Lenz vector. Additionally, if x and y are conserved, x + ay is conserved as well, for all values of a. So if there are two, there are an infinite number.
PF Patron
P: 10,403

From wikipedia, it lists a few things seperated into "exact laws" and "approximate laws".
 A partial listing of conservation laws that are said to be exact laws, or more precisely have never been shown to be violated: Conservation of mass-energy Conservation of linear momentum Conservation of angular momentum Conservation of electric charge Conservation of color charge Conservation of weak isospin Conservation of probability density CPT symmetry (combining charge, parity and time conjugation) Lorentz symmetry There are also approximate conservation laws. These are approximately true in particular situations, such as low speeds, short time scales, or certain interactions. Conservation of mass (applies for non-relativistic speeds and when there are no nuclear reactions) Conservation of baryon number (See chiral anomaly) Conservation of lepton number (In the Standard Model) Conservation of flavor (violated by the weak interaction) Conservation of parity Invariance under Charge conjugation Invariance under time reversal CP symmetry, the combination of charge and parity conjugation (equivalent to time reversal if CPT holds)
P: 1,060
 Quote by Drakkith Yeah, It all depends on what you mean by "mass". Converting electrons-positrons to gamma rays removes the "mass" and turns it into energy or momentum or whatever.
Would it then be correct to say that a conservation of matter doesn't exist, but a conservation of mass does, seeing as energy does possess mass?
PF Patron
P: 10,403
 Quote by 1MileCrash Would it then be correct to say that a conservation of matter doesn't exist, but a conservation of mass does, seeing as energy does possess mass?
As wikipedia put it, I'd call it Conservation of mass-energy.
 P: 15 The concept of mass–energy equivalence connects the concepts of conservation of mass and conservation of energy, which continue to hold separately. The theory of relativity allows particles which have rest mass to be converted to other forms of mass which require motion, such as kinetic energy, heat, or light.From WkiPedia.

 Related Discussions Classical Physics 13 Special & General Relativity 13 Advanced Physics Homework 2 General Physics 1 Introductory Physics Homework 1