This document discusses simple harmonic motion and modeling it using sinusoidal functions. Simple harmonic motion is motion that repeats, such as a buoy bobbing up and down in waves or a piano string vibrating. It can be described using a sinusoidal function of the form f(t) = a cos(bt + c) + d, where a controls amplitude, b controls period, c controls phase shift, and d controls vertical shift. The document provides examples of writing sinusoidal functions to model real-world situations involving simple harmonic motion, such as a bobbing buoy or vibrating piano string. It also discusses using the functions to make predictions about the motion.