The problem: L = 0.5. Pendulum of L is displaced angle of 0.1 rad and then released from rest. Determine resulting motion. Ok, so I know it's going to be a second order DE of this kind which I will need to solve: theta''(t) + (g/L)theta(t) = 0; so theta(0) = 0.1? then what about theta'(t)(0)? is it just = 0? and what is it exactly anyway? if derivative is a rate of change with respect to time? rate of change of angle? Thanks for any explanation/source.