This document discusses Hooke's law, which states that the force (F) needed to extend or compress a spring is proportional to the displacement (x) of the spring from its resting position. F = kx, where k is the spring constant. It provides examples of calculating the total extension of springs connected in series or in parallel. For springs in series, the total extension is the sum of the individual extensions. For springs in parallel, the total extension is the average of the individual extensions.