# Difference between weak and strong interactions?

This was a statement given in my class:

"Strangeness is conserved in the strong and electromagnetic interactions, but not in a weak interaction "

But could someone please tell me how we differentiate between a weak and a strong interaction? An example would be helpful.

• Can you clarify what you are asking. Are you asking how we distinguish between the interaction in a scattering experiment, or are you asking how the fundamental mechanisms differ? – John Rennie Jun 11 '14 at 9:18
• There is a sense in which this is like asking how we differentiate gravity from electromagnetism. We differentiate them by the different laws they follow and the different effect that arise from them. – dmckee Jun 11 '14 at 20:19

Relative to the strong interaction the weak one is $10^{-6}$ in coupling strength. The couplings enter squared when calculating probabilities from the state functions.
Neutron decay is the classical example and where the weak interaction first was observed. In general, the typical lifetime for the strong interactions is less than $10^{-23}$ seconds, whereas that for the weak interactions can be anything from $\sim 10^{-11}$, to years, depending on the isotopes.