Vibration as a Form of Artificial Gravity

French scientists have studied how the transition from liquid to gas and back again slows down in a weightless environment and how an artificial form of gravity can be simulated using high-speed vibration of the sample. This work has implications for work in space, where fluids don't behave the way they do on the ground.

Past studies have shown that vibrating an astronaut's legs and feet helps to prevent muscle decay or bone decalcification. Daniel Beysens, a researcher at the Commissariat a l'Energie Atomique (CEA, dbeysens@cea.fr) and his colleagues study this problem at the much more basic level of individual bubbles and droplets, and what happens to them when you add or subtract the effects of gravity.

Movement between liquid and vapor states is aided by buoyancy: bubbles rise and droplets fall. But without gravity these actions cease and liquids condense only by the haphazard and slower process of collision between droplets or bubbles. In the new experiment a 20-cubic-millimeter sample of liquid/gaseous hydrogen was levitated in a strong magnetic field; the field grabs onto the magnetic moments of the H2 molecules, helping to suspend them. This essentially creates an artificial weightlessness (only about 1% of Earth's gravity remains) and allows one to see how capillary forces and "wetting" (the process by which a liquid layer builds up on a surface) are dominant in a freefall environment. Then some of the effects of gravity are artificially added back in, this time in the form of high-speed but low-amplitude vibrations.

The vibrations cause motion in the fluid, which induces effects that resemble gravity. Bubbles and droplets go "up" and "down" again when the vibration is turned on. As far as simulating gravity, vibrations seem to work. ( Beysens et al., Physical Review Letters, 15 July 2005)