Ever wonder why a boomerang comes back?

Ever wonder why a boomerang comes back?

By Steven Law, KSL.com Contributor | Posted - Aug. 2, 2012 at 11:45 a.m.



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There are two types of boomerangs: hunting boomerangs and returning boomerangs. When most of us think of boomerangs, we probably picture returning boomerangs, a curved stick that, when thrown, will return to the one who threw it.

A boomerang returns to its thrower due to the application of some complex laws of physics. Given the complex physics involved and the fact that returning boomerangs have been used since primitive times, anthropologists believe that returning boomerangs likely evolved by accident, or trial and error, from hunting boomerangs.

So how does it work? A returning boomerang has two physical properties that make it work the way it does. The first is its curved, banana-shaped design. This gives the boomerang two component parts, whereas a straight stick flying through the air has only one component part. The boomerang’s two opposing wings meet at a central point, and when it’s thrown, the boomerang spins around that central point. This action stabilizes the boomerang’s motion as it flies. But this alone won’t make the boomerang return.

Boomerangs have a second property, and it’s this second property that makes it curve through the air and return: each wing of a boomerang has an airfoil shape, which means that the wing's leading edge is rounded at the top and tapers to flatness on its back edge, just like an airplane wing. The rounded edge of an airfoil causes the air traveling over it to move more quickly than it does the flat underside of the wing. The wing lifts because it has greater pressure below it than above it.

Boomerang trick shots

A boomerang has two motions acting upon it. It has a spinning propeller motion (a boomerang is essentially two-thirds of a propeller that’s not attached to an axis), as well as the motion of flying through the air in the direction it was thrown. Thus, whichever wing is at the top of the spin is also moving in the same direction as the boomerang’s forward motion. This means that the air travels over the boomerang’s top wing faster than it does the bottom wing. The faster air travels over an airfoil, the more lift that wing has. Consequently the top wing will have more lift than the bottom wing, and the boomerang constantly "lifting” in that direction is what makes it fly in a circle.

Oh!

A right-handed boomerang flies in a counter-clockwise direction, a left-handed boomerang flies in a clockwise direction.

Traditional boomerangs have two wings, but modern boomerangs are made with three and four wings. The additional wings give the boomerang more airfoil space and the more airfoil space the easier it is to return, says Dana Larabee, vice president of Boomerangs.com, a California company that designs, manufactures and sells boomerangs.

Hunting boomerangs have been used for thousands of years, says Saulius Pakanlis, an engineer who wrote his doctoral thesis on the physics and history of boomerangs. Pakanlis is probably the world’s leading expert on all things boomerang.

Ever wonder why a boomerang comes back?

Australian Aboriginal boomerangs have been found that are as old as 10,000 years. Contrary to common belief, boomerangs didn’t originate in Australia (though Australia’s Aboriginal people did discover them independently). Non-returning boomerangs have been found all over the world. The oldest known non-returning boomerang, found in Poland, dates from about 20,000 years ago, writes Pakanlis.

A hunting boomerang is made from a long, heavy piece of wood. They’re typically about three feet long, with sharpened edges. The boomerang’s sharpened edges allow it to cut efficiently through the air, allowing the hunters to make more accurate throws. When hunters throw their boomerangs at prey, the heavy, blade-like weapon injures or kills the prey. Because returning boomerangs curve when you throw them, they are not well-suited for hunting, as it’s hard to hit your target.

Early Aborigines understood that sticks with sharpened and shaped edges made them travel through the air more truly than just an ordinary stick. Aborigines experimented with their boomerang’s shapes and edges looking for the most optimal shape and through that process stumbled upon a shape of boomerang that returned when they threw it, says Pakanlis.

It’s unlikely that returning boomerangs were used for hunting, but they continued to be made, and even perfected upon, and used for recreational and entertainment purposes.

To throw a boomerang, hold it in a vertical line with the V-point, or elbow, facing toward you, with the boomerang’s flat side facing to your right. Hold the boomerang by the end of the bottom wing, with a pinch-like grip. Bring the boomerang behind you and bring it forward in the same motion as throwing a baseball. Keep it vertical when you throw it. When you release the boomerang, snap it forward with your wrist to give it extra spin. The boomerang will travel in a counter- clockwise direction and gradually flatten out on a horizontal plane like a Frisbee as it returns.

If you'd like to read Steven Law's past science articles, you can find them at www.curiosity101.com

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