60秒科学:Maple Seed Flight Aerodynamics（在线收听）

What do a hummingbird, a moth, and a maple tree have in common? They all use a similar trick to fly. Okay, okay, a maple tree doesn’t fly. But its seeds kind of do. Maples make those little whirlybird seeds you see spiraling down in droves each spring. Their papery little wings keep them aloft so they can find a good place to germinate and make a new maple. But how they manage to fall so slowly has been a bit of a mystery—until now.

Scientists filmed maple seeds as they wafted through a smoke-filled wind tunnel. And they found that a spiral of air develops on top of each falling seed’s wing. That vortex generates lift, and acts like a miniature tornado that sucks the seed up. The study appears in the June 12th issue of the journal Science.

The same type of vortex also helps bats, hummingbirds and insects soar. So it seems that plants and animals have both stumbled on the same aerodynamic approach to battling gravity. Which explains why the acorn might not fall far from the tree, but maple seeds can really go the distance.

—Karen Hopkin