⇒ In quantum physics, there are many different quantum number conservation laws i.e. situations where the properties or physical quantities after an interaction are the same as before an interaction

• For example, we have looked at the conservation of the lepton number, the baryon number and strangeness

⇒ In addition to this three other quantities are always conserved in an interaction:

• Charge (Q)
• Momentum (p)
• Mass-energy (E = mc²)

⇒ Strangeness is the only quantitiy that is not conserved in an interaction i.e. it is conserved in strong interactions, but not weak interactions (as the strange quark changes flavour)

⇒ Also see our notes on:

• Introduction
• Quarks
• Fundamental Forces
• Feynman Diagrams
• Classification of Particles