Sprocket wheel

HOW

Turn the crank and observe the gears, enclosed in glass cover.

WHY

Under the glass cover, there are 15 large wheels, each with 120 teeth, and 14 smaller wheels,each with 22 teeth. The smaller wheels are fixed immovably to the larger ones in such a way that the smaller wheels drive the next larger wheels.

One full rotation of the first, large wheel, means one full rotation of the first, small wheel, but also 22/120 rotation of the second large wheel, (22/120) x (22/120) rotation of the third, large wheel, etc. The last large wheel will rotate by the fraction 22/120 raised to the 14th power during the full rotation of the first wheel. This means a shift of the teeth of the last wheel by one-millionth of the thickness of a human hair. Such a small shift and the small clearances between the teeth mean that the last wheel can be immobilized, and the whole system still works. For the last, yellow wheel to make one full rotation, the first must rotate more than 20 billion times.