Stand facing a mirror, and hold the disk in front of you. Be sure the disk is mounted on the pencil so that the horses are facing the mirror. Close one eye, then spin the disk and watch its reflection in the mirror through one of the slits. Concentrate your attention on one of the horses, and you will see it gallop! Try spinning the disk faster, then slower, then in the opposite direction. Compare your results.
Try these other experiments:
Have a friend hold out a hand so you can see it through the spinning disk. Ask your friend to move the hand from side to side. Notice that the movement you see is jerky rather than smooth. Have your friend move his or her hand rapidly, then slowly. Notice that the amount of jerkiness changes as the speed of the hand movement changes.
Let water run slowly enough to produce a stream that breaks up into separate droplets as it falls. Place a black background behind the well-illuminated drops of water. Look through the spinning stroboscope and watch the water droplets fall in slow motion. Vary the stroboscope’s speed and see if you can make the water droplets stand still or even look like they are moving upward.