Often it is necessary to
measure the rate at which objects rotate. An instrument which is capable
of doing this is called a stroboscope. Stroboscopes give flashes of bright
light. This light is then made to fall on the rotating object. The rate at
which the stroboscope flashes light is then adjusted so that the light
falling on the rotating object appears to be stationery. At this point of
time the frequency of flashing of the stroboscope is the same as that of
rotation of the object. In this way the rate of rotation of rotating
objects can be determined.
Let us now undertake a simple experiment to demonstrate this concept.
You Will Need
- A white cardboard disc, about
4" - 5" in diameter
- A hand drill
- A nail
Take a cardboard disc and
divide it into eight equal pie shaped sections.
Colour alternate sections red so that you have four white and four
Now pierce the nail through the exact centre of the disc. The nail
should be firmly attached to the disc and turning the nail should
turn the disc.
Open the chuck of the hand drill by rotating the screw and insert
the other end of the nail in the chuck. Tighten the chuck so that
the nail is firmly gripped by the chuck
Rotate the handle of the chuck. At
first the disc will appear to be moving backward, as you increase
the speed a point will come where the disc appears to be perfectly
still. If you further increase the speed the disc will appear to
be moving rapidly forward. This experiment demonstrates the