Teaching
The following are supplementary materials I've created for use in courses I've taught. They shouldn't be considered to be entirely self-contained, but, combined with other sources/a pre-existing knowledge of the topic, aim to reinforce or expand upon some aspect of physics.
An illustration and discussion of the electric potential for two point charges of equal and opposite magnitude [PDF]. Appropriate for an introductory E&M class.
Four gifs showing the normal modes of coupled oscillating systems: one, two, and three carts (of identical mass) connected by identical springs; and the three vibrational + one rotational modes of a triangle of equal masses connected by equal-stiffness springs [ZIP]. Made for an upper-level Mechanics course, but you could probably use them conceptually in an introductory course.
Two graphics demonstrating how spatial interference works for two pure-tone sources, with some explanation; as well as three sound files demonstrating temporal interference (beat frequency) for two pure tones [ZIP]. Appropriate for an introductory course.