Episode 9: Electric Didgeridoo

Science off the Sphere

Astronaut and chemist Dr. Don Pettit does physics demos that are out of this world. Currently on board the International Space Station, Dr. Pettit presents fantastic physics that can only be demonstrated in micro-gravity.


Episode 9: Electric Didgeridoo

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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