Why does a boomerang return to its thrower? What’s the science behind it?

Boomerang is a special type of throwing stick that is sickle shaped with arms slightly twisted in opposite directions as in a propeller. The two arms are at an angle of anything between 70 and 120 degrees, with one arm of a bit longer than the other and tips always bent a little upwards. The principle involved in its characteristic flight is simple, though for most people it has remained a mystery. The boomerang is an airfoil. It has more or less flat lower surface, while the upper surface is cambered. This peculiar shape, also common in aircraft wing, has a property of splitting up the oncoming air mass unequally. The air flows more quickly on the curved side with the result that less pressure compared to the flat side where air flow is slower.

A boomerang is thrown by holding it near the tip (flat side toward the thrower) with a strong over arm sweep and flicking the wrist down at the last moment to produce spin. The boomerang travels forward, spinning like a wheel for all of its effective range of about 50 meters. Because the high-pressure flat side is towards the right-handed thrower, it is continuously pushed farther to the right so that the path it describes is that of an arc. Thereafter, if nothing is struck, the boomerang flattens out and swings to the left. Soon, it rises high in the air and because greater force of the lift is not left of the center, the boomerang turns left toward the thrower. The flight path now is similar to an aircraft turning left, with its right wing slightly raised.

The boomerang of the Australian aborigines (from whom the term is derived) is made in two types. The smaller variety (30 to 75 centimeters long) is used only for sport. It is this boomerang with describes a rough circle and returns to the thrower. Using it requires great skill. The larger boomerang (60 to 90 centimeters long), weighing up to 675 grams, does not return and is used for hunting. If a flock of birds is the target, however, the smaller variety works just as well. It is interesting to note that aborigines of Andaman are also known to have used boomerangs, though of slightly different appearance.

More reading:
Boomerang (Wikipedia)

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