Using a reciprocating pump and a strobe light, we can make water drops appear to fall down (or up) in slow motion.
This illusion is due to the periodic nature of the pump: each droplet forced out of the tube is almost identical to the
preceding droplet so our eyes perceive the droplets moving slowly rather than falling quickly. You also can freeze-frame this
video and use the ruler to make a crude measurement of the acceleration of gravity.
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