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 direction of $d\vec r$ is tangent to a path between two nearby points FIXME: Tangent to what path? How is this useful? Representations used No activity! NEEDS NAME $d \vec r$ ENTER LONG DESCRIPTION New representation New needed for concept