Funky Vision

Set a computer screen to a blank white screen. I do this by opening a NEW Word document. Strike a tuning fork and hold it in front of the screen. What do you see? Is it different if you orient the fork horizontally and vertically? Why? The screen, like all tube-based video monitors, acts as a strobe light since it flickers just faster than we can notice. So if you hold the fork horizontally, it appears the fork is vibrating slower than if held in front of another background. When held vertically, you get a really weird wavy effect. This is due to the screen's uneven lighting. It will light by sweeping electrons across itself. When the electrons are present, you see the fork. When the electrons aren't there, you don't. It happens so fast that your brain actually gets confused. [Again, thanks to Jewitt,]
A similar effect is to just have kids look at the blank white screen and hum loudly. They will notice a "sweeping" effect caused by the intermittent electron scanning.

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