NYU researchers found a way to create gear mechanisms using water through fluid mechanics — how liquids and gases interact with themselves and other objects. 

Published in Physical Review Letters, the scientists powered one active cylinder to rotate while submerged in a glycerol-water solution, and left another passive cylinder unpowered in the solution. The researchers discovered that rotating the active cylinder, through the movement of the surrounding solution, could cause the passive cylinder to also spin — like a set of gears or pulleys.

“We found out that fluids can act as both gears and belts, that is, they can engage on the closer sides of two rotors like teeth on a pair of gears or engage on the far sides like a belt around a pair of pulleys,” co-author and Courant associate professor Leif Ristroph wrote to WSN. “Fluids are surprisingly multifunctional when it comes to communicating forces and motions between objects.”

Traditional gears, which are made of wood, metal or plastic, can be fragile and must be perfectly interlocked to work. Fluid gears, however, can spin each other without physically touching, preventing jams caused by manufacturing defects that prevent normal gears from interlocking with each other.

Ristroph wrote that fluid gears could also have advantages over traditional gears because they could control each other’s speed or rotation just based on their proximity to each other.

“Normally the speed coming out a motor is done by ‘changing gears,’ that is, literally using gears of differing sizes to change rotation rate,” Ristroph said. “The same can be accomplished for fluid gears just by changing how close or far the input and output rotors are … we can even change the direction of rotation by the same operation.”

The study also brings researchers across departments, as Ristroph’s co-authors are affiliated with the CAS physics department and NYU Shanghai.

“We’re excited to continue to serve as a link between math and other areas, and we’re especially excited by all the developments at the Tandon School,” Ristroph said. “I can foresee many productive interactions and collaborations in the future.”

Contact Justin Liu at [email protected].