How to make a stroboscope

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Making a stroboscope
You Require
One Cardboard disc 4”in diameter
One hand drill
One nail
Method
Take a cardboard disc 4” in diameter. Divide the circle into eight pie shaped sections. This can be done by drawing a line through the centre of the circle and then drawing another line at right angle through it. This divides the circle into four equal parts. Now, divide each of these four parts into halves thus, producing eight sections. Leave one section white and colour the next. In this way, you will have white sections and four coloured sections.
Now, force a nail through the centre of the circular disc in such a way that the cardboard cannot turn unless you turn the nail. If necessary, you can glue the nail .
Insert the nail into the chuck of the hand drill. Now, turn the handle of the drill. As you change the speed of the drill, the disc will appear as if it is standing perfectly still. If you reduce the speed slightly at this position, the disc will appear to be turning backwards. If you increase the speed, the section will move rapidly forward. This demonstrates the stroboscopic effects.