Prerequisite concepts Vector Calculus $d \vec r$ is a small displacement vector $d \vec r$ represents a small displacement vector (i.e., it points along the direction of a step with a magnitude equal to the length of that step). New prereq concept Vector Differentials New taught by The magnitude of $d\vec r$ is the distance between two nearby points FIXME: What's the point of this concept? Representations used No activity! NEEDS NAME $d \vec r$ ENTER LONG DESCRIPTION New representation New needed for concept