Monday, June 23, 2014

Did You Know...What Makes a Boomerang Come Back ?

The boomerang is generally considered to be the first manmade flying machine.
But it all started with non-returning boomerangs.Weapons that have been used for at least 20,000-30,000 years, with the oldest known example carved from a mammoth’s tusk. These boomerangs were strictly adapted for a straight flight and to stay in the air as long as possible (if thrown correctly, that's for sure). The hunter was then able to throw the primitive boomerang great distances and hit an animal to be eaten. These animals were often small-game, but even the likes of big animals (kangaroo or emus) can be  injured by a decently weighted boomerang such that the animal can no longer outrun the hunters. Possibly while shaping a non-returning boomerang, someone accidentally carved a boomerang into a shape that, when thrown correctly, came careening back toward the owner. It wasn’t exactly useful for hunting or warfare; it was difficult to aim; and if it actually hit its target, it wouldn’t come back anyway. Most scholars believe that, because returning boomerangs don’t serve much of a functional purpose in hunting, they were simply used for sport, possibly first by the Australian aborigines, though Ancient Egyptians and many other cultures also made them. It could be quite interesting for you to know Tutankhamen actually had a collection of returning (and non-returning) boomerangs. But actually the Early Australian settlers believed that the boomerangs they saw the aborigines carrying were wooden swords.


While there are numerous different ways to make a boomerang, traditionally, the returning ones are lightweight, made of wood, and consist of two separate wings which meet at an angle in the middle. That middle section forms the central point around which the wings will be able to spin, stabilizing the flight pattern. But unlike an airplane or helicopter propeller, which starts spinning while the vehicle is completely still, you throw the boomerang, so that in addition to its spinning propeller motion, it also has the motion of flying through the air. But how a returning boomerang works? What's the physics behind it? 

When a boomerang is thrown, it starts a spin with a wing at the top, while the other is at the bottom. whichever wing is at the top of the spin at any one time ends up moving in the same direction as the forward motion of the throw, while whichever wing is at the bottom of the spin is moving in the opposite direction of the throw. This means that while the wing at the top is spinning at the same speed as the wing at the bottom, it is actually moving through the air at a higher rate of speed. When a wing moves through the air more quickly, more air passes under it. This translates into more lift because the wing has to exert more force to push down the increased mass. So, it's as if somebody were constantly pushing the whole spinning propeller of the boomerang at the top of the spin. And that's when it starts to turn...


When you push on one point of a spinning object, such as a wheel or boomerang, the object doesn't react in the way you might expect. As we just said, air flows faster over the top of the boomerang, creating more lift than over the bottom. So, these unequal forces generate a torque, and you might expect that torque to flip the boomerang over, but it doesn't. And that's  because it's thrown with a very fast spin. So that spin means that the boomerang has an angular momentum, a great amount of it. To know the direction of it, you have to put your fingers of your right hand in the direction of rotation, and the thumb points in the direction of the angular momentum. So, as it's spinning, the torque actually changes the angular momentum, and it changes it in the direction of the torque. In the case of you throwing the boomerang, the torque would be directed towards you. So the angular momentum is changed to point around at you, which allows the boomerang to execute its curved path and come back to where it started. This phenomenon is called Gyroscopic Precession.

Of course, as anyone who’s ever tried to throw a boomerang knows, you also have to throw it correctly in order to get it to come back to you. You need to throw it somewhat vertically, holding it by one wing, with the other wing pointed up, with the centre pointing toward you. And now this ancient weapon has truly become a never-failing way to have fun.


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