Periodic: t, time is takes to oscillate over the same path (units: seconds) Equilibrium position: spring"s natural length in which it exerts no force on mass. If spring compresses or stretched, spring force will appear: restoring force, fs = -kx, k = spring constant (n/m, x = distance from equilibrium. Simple harmonic motion (smh): oscillating system when net restoring force is directly proportional to the negative of displacement. Shm only occurs without friction (me is constant: at xmax, e total = (1/2) ka^2, ke = 0 because v = 0, total mechanical energy of a simple harmonic oscillator is proportional to the square of the amplitude. Sfu: at x=0, e total = (1/2) mv^2, pe = 0 because mass is in full motion, at intermediate points, e total is both pe & ke, (1/2) ka^2 = (1/2) kx^2 + (1/2) mv^2. Acceleration is proportional to fs & distance: ma = f = -kx.