Summary

• Know how spins behave and how to manipulate them.

• Know we can't measure single spin. Start to look at density of spins and integration over groups of spins.

• Have alluded to the fact that all spins will eventually ``relax'' back to equilibrium.

• Also know that $\omega = \gamma B$ is always at work, and if $B$ is not the same everywhere spins will precess at different rates in different locations. Consider 2 types of ``static'' fields
  1. Externally applied fields
  2. Internally applied fields; spins on one another, chemical environment

• Consider these factors, and how they effect the behavior of the spins.