– A group of mathematicians have solved the decades-old problem of what would happen to a sprinkler head if it was submerged and sucked in water instead of gushing in water.
– The problem has been known as Feynman's sprinkler problem since the mid-20th century, when a graduate student at Princeton University solved it in the 1940s.
Previous experiments have produced conflicting results, but a new ultra-low-friction rotary bearing has been built to allow a custom-made reverse sprinkler to spin freely.
The device was designed to run indefinitely and the researchers used colored dyes, laser-scattering microparticles,
and high-speed cameras to visualize and record the rotation of the sprinkler and water flows.
The team found that the reversed sprinkler spins in the opposite direction
when taking in water as it does when ejecting it, and the cause is subtle and surprising.
The findings could be applied to engineer technologies to harvest energy from flowing air or water by generating motion or forces.