HOW COME? The returning boomerang
How come a boomerang comes back to you? asks reader Ife Oshikanlu.
Like yo-yos, kites and radio-controlled airplanes, a boomerang is a toy that returns to you -- but with no controller or string required to reel it back. A toy that returns to your empty hands might seem modern, but human beings have been playing with the ultimate come-back toys for thousands of years.
How did people invent boomerangs? Archeologists have found that early humans threw heavy wooden sticks to kill animals for food and hides. They also used the weapons in battles with rival tribes. And these so-called throwing sticks were designed with a slight bend in the wood. While experimenting with carving such throwing sticks, hunters probably made the first returning boomerangs.
The original throwing sticks were used for hunting, but returning boomerangs were designed for fun and sport. In old movies, boomerangs swished through the air, knocked down a bad guy or attacking animal, and spun obediently back. In real life a boomerang that strikes an obstacle simply plunks to the ground.
So what's the difference between a boomerang and a traditional throwing stick? One difference is a boomerang's feather-light weight. The other is its shape: Boomerangs are made in rounded V-shapes, while wooden throwing weapons are much straighter. A boomerang in flight is really a kind of freely rotating wing, unattached to an airplane, helicopter or bird.
According to physicists, boomerangs come back for two main reasons: the shape of their two arms, and the way in which they're thrown. Like an airplane wing, the underside of a boomerang arm is flat, while the top is curved. This wing shape causes air rushing over the boomerang to lift it up. But boomerang arms are different from the average plane's wings. On a boomerang the curved top of one arm leans into the wind; on the other arm the curve leans away. If an airplane had such opposing wings, it would have a hard time flying straight. So does a boomerang -- and that's the idea.
How a boomerang is thrown is also crucial to its eventual return. The boomerang is held vertically, with its flat side pointing away from the thrower's body. Then, with a snap of the thrower's wrist, it is tossed into the air. As it flies away, the boomerang is both traveling forward while frantically spinning end-over-end.
As the boomerang travels forward, it's tugged back a bit each time an arm spins under. This creates pressure on top of the boomerang -- and the boomerang gradually takes a left turn. As the boomerang traces a big circle in the air, it "lies down" like a rotating helicopter blade. If all goes well, the boomerang tumbles back.
