Nature may have a few things to teach tennis players about backspin.
The hairyflower wild petunia (Ruellia ciliatiflora) shoots seeds that spin up to 1,660 times per second, which helps them fly farther, researchers report March 7 in Journal of the Royal Society Interface. These seeds have the fastest known rotations of any plant or animal, the authors say. Plants that disperse seeds a greater distance are likely to be more successful in reproducing and spreading.
Glue that holds the flower’s podlike fruit together breaks down on contact with water, allowing the fruit to split explosively, launching millimeter-sized seeds. Little hooks inside the pod help fling these flattened discs at speeds of around 10 meters per second.
Using high-speed cameras that record 20,000 frames per second, the researchers analyzed the seeds’ flight. “Our first thought was: ‘Why doesn’t this throw like a Frisbee?’” says Dwight Whitaker, an applied physicist at Pomona College, in Claremont, Calif. Instead of spinning horizontally, most seeds spin counterclockwise vertically, like a bicycle wheel in reverse.
Whitaker and his colleagues calculated that backspin should help stabilize the seeds as they travel through the air, reducing drag. Experiments backed this up: Stable “spinners” had less drag on average than “floppers,” seeds that tumbled as they fell. Simulations predict that lower drag lets spinners travel 6.7 meters on average — more than twice as far on average as floppers.
TAKEN FOR A SPIN Watch as the fruit pod of the hairyflower wild petunia explosively splits open, sending its seeds spinning. Moisture usually triggers this action, but in this experiment, a pinch worked as well. Some seeds have a rapid backspin that gives them stable flight, while other seeds, known as floppers, are unstable and don’t fly as far.