Mathematics – angles on parallel lines. Used the document camera to write out the information, instead of putting it on the board. Was that why the kids were more attentive during the writing stuff down drudgery? Them being able to see how to arrange the information on paper is surely helpful.
Physics – refraction of light! I opened with a demo where we went outside, linked arms and marched from pavement to grass. Kids slow down when they hit the grass, and the whole line changes direction! It was super effective and explaining refraction – I still remember taking forever to tease it out myself when I was an 11th grader.