The Dance of the Hemispherical Water Droplets: Sound Waves in Space
Water covers approximately 70 percent of Earth's surface and the human body contains up to 78 percent water, depending on body size. Yet, water seems to be taken for granted here on Earth. But if you travel to an orbital altitude of about 250 miles, water starts looking pretty interesting. Especially to astronaut Don Pettit on-board the International Space Station.
In recent Science Off the Sphere episodes, Don's already shown us the dance of water droplets around knitting needles and how centrifugal force affects antibubbles in microgravity. Now, he's pulling out the H2O again to show us how it interacts with sound waves.
Don takes the grate off a set of USB-powered stereo speakers and hooks up his MP3 player to start the show. He puts a drop of water on one of the speaker cones and plays some low frequency tones from 20 Hz to 30 Hz, which turns a small hemispherical blob of water into a wildly oscillating beast. Here on Earth, gravity would just flatten the water out. But in near zero-gravity space, things get crazy and water even starts squirting out of the hemisphere.
He then plays around with slower speeds and other frequencies up to 40 Hz. But the real show doesn't take place until he jams the ZZ Top. Though water does no behave this way to sound waves on Earth, it does remind me of watching cornstarch dance on speakers. Even the wildly sophisticated movements of ferrofluid reacting with magnets.
Do you know why Don uses low frequencies to get the water to jiggle? Let us know in the comments below! Or share you answer with Science Off the Sphere.