He made a device for a child to study physical processes, in the head of optics, I remember at school they did something similar in physics with the only difference being that the drive was manual, by analogy with the device of the English physicist Bragg.
Dismantled the engine and gear with belt from an old printer.
I made a circle out of cardboard. Diameter 140 mm and small radius 3.5 mm
Cut a slot
Painted one half white, the other black
The result was such an analogue of the device of the English physicist W. G. Bragg. If the instrument is powered by a battery or 18650, then you can make a speed regulator for tuning, I have an adjustable LBP so I did not need a regulator.
How to explain to the child the principle of this experience? Why does the color of the LED change during rotation?
Our eyes have three kinds of color sensitivity receptors. Each of them contains photochemical sensitive pigments. The three primary colors — red, green, and blue — have their own receptors. When it hits the retina, red light produces a photochemical reaction, as if neutralizing itself. A signal is created that enters the brain through the optic nerve and causes a sensation of a certain color. With the strong influence of this radiation, the brain automatically underestimates the sensitivity of the corresponding receptors. Have you noticed that when you close your eyes in bright sunlight, is only the red color felt? It is, our retina passes only red through the eyelids.
When the LED is blocked by the bright side of the moon, the eyes receive a maximum spectrum of white light and sensitivity to red is reduced. In our eyes, the signals reflected from the bright side of the moon include all receptors, but not red. Having received the light from the difference of red from white. We see shades of green light or green, when the LED is blocked by the dark side of the moon, the receptors in the eyes are restored, and we only see the red LED. So changing the red LED to any other available LED, and changing the rotation and speed of the disk moon, we get a diverse palette of colors and invaluable knowledge in the field of optics. Good luck to all!