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Challenge Question: Why does the amount of water on the speakers affect how often droplets are ejected?
Challenge Answer: The more water, the larger the surface area of the sphere of water. The speakers exert a force on the sphere of water, increasing the pressure inside the sphere. Pressure is F/A, so a given sound will generate a lower pressure in the sphere. If the pressure per unit area is strong enough to overcome the surface tension of the water, a droplet is ejected. Therefore, more water means larger surface area, which means lower force per unit area on a water droplet.
Challenge Winner: Zach Mitchell from Chapel Hill, NC