Quadcopters, or drones, have come into wide use recently for a variety of applications including video inspection of otherwise inaccessible areas, real estate sales, and entertainment. Students are interested in them and in some cases own their own. The combination of high mobility, relatively low price, and autonomous operation is quite…

Discusses the nature and orientation of the forces that allow an engineless airplane (a glider or sailplane) to fly. A glider flying at constant velocity provides a nice example of an object moving under the action of several forces that add to zero. (WRM)