Have you ever wondered why wheels in movies start rotating clockwise, then reverse in the counterclockwise direction, then slow down to standstill? If the wagon or the car keeps accelerating, the wheel starts rotating clockwise again, at a lower speed, however. Another related wonder occurs with stroboscopes. Stroboscope is a short-duration, adjustable-high-frequency, and high-intensity flashlight source made of a xenon discharge lamp or high-power light-emitting diodes (LED.) It is used to find the rotational speed of wheels, fans, and the like. The flash source briefly illuminates the rotating object. The flash frequency is gradually increased until the object eventually appears stationary.