Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 08/01/2008 12:49:23
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How does a boomerang work and what is the principle behind that?
Asked by Anand, Colchester
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This question was answered by Dr Hugh Hunt, Dept. Engineering, Cambridge University:
That’s a really good question. A boomerang goes around on more or less a circular path. The motion is really just fantastic. It’s a combination of various physical principles for example, aerodynamic lift and circular motion. You’ve got to get these physical principles just right when you throw the boomerang which explains why boomerangs are a bit tricky to throw.
Think of the two arms of the boomerang as being just like the wings of an aeroplane. The faster they move through the air, the more lift they generate. Unlike an aeroplane a boomerang spins as it moves through the air and the combination of spin and forward speed means that some parts of the boomerang are moving faster than others. This means that the aerodynamic lift is not uniform over all parts of the boomerang. The wings of an aeroplane are horizontal so the lift is upwards. The wings of a boomerang are sideways so the net lift is towards the centre of the circle that you see the boomerang move on.
There’s one more important physical principle. The non-uniform lift generates torque or a moment, a twisting force – whatever you like to call it and this causes the gyroscopic effect to come into play. A spinning boomerang is really no different to a spinning gyroscope and the gyroscopic effect makes the boomerang turn around nicely, at just the right rate. It really is magical and the best bit of all this is that the entire explanation rests on Newton’s laws of motion.
There’s one more little catch, and that’s to do with gravity. You need a bit of lift force directed upwards. Otherwise the boomerang will just drop down to the ground in no time. This explains why you need to throw a boomerang with a little bit of a tilt. It also explains why a good boomerang will increase its tilt angle as it slows down. This is called laying over. The boomerang that has slowed down and laid over is really easy to catch.
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I think it's a combination a wing shape and precession, but I'm only guessing.
By some coincidence I was give one for Christmas and there was me thinking "not more coat hangers" before I opened it.
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Perhaps a more intriguing question would be, why doesn't any old stick come back if thrown with the technique as a boomerang?
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A Boomerang is shaped like a plane wing, one wing longer and fatter that the other.... As it spins it receives a lift, just as the plane wing. However due to the lack of symmetry one wing is lagging compaired to the other, which as a result will glide quicker through the air thus causing the curved trajectory. IF the boomerang is well balanced and thrower is experienced, he or she can cause the length of the flight of the boomerang to complete a full circle, thus landing back into the thrower's hand.
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One can get quite strange behaviour from matches and rulers by employing the spin technique, if you take a match and like clicking your fingers but with a match between them the match actually climbs after dipping, just trying to remember how to get the ruler, to do the same, but as a result of spin.
it also sort of flies.
The boomerang when thrown, should have the leading edge pointing towards you: U<
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I thought the reason was that as the boomerang moves through the air, 1 wing is moving forwards (relative to the boomerang's direction of travel) while the other is moving backwards. The wing on the inside - the 1 that is moving backwards - will consequently get less air travelling over it and, hence, less lift. As that wing revolves and gets to the outside, it will then be travelling forwards and the other will be travelling backwards. It is always the outside wing, the 1 moving forwards, that generates more lift. That will cause the boomerang to travel at an angle with the outside wing always slightly higher than the inside wing. That means the overall lift is not vertical, but slightly inclined towards 1 side. That will cause its trajectory to curve in that direction.
The principle is similar to a helicopter's rotor, but that uses variable attack angles (or pitch) to generate vertical lift. Without variable pitch the helicopter would behave like a boomerang & fly round in circles.
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There’s one more little catch, and that’s to do with gravity. You need a bit of lift force directed upwards. Otherwise the boomerang will just drop down to the ground in no time. This explains why you need to throw a boomerang with a little bit of a tilt. It also explains why a good boomerang will increase its tilt angle as it slows down. This is called laying over. The boomerang that has slowed down and laid over is really easy to catch.
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So, if you throw a boomerang with a depression angle, it won't come back?
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How does a boomerang work and what is the principle behind that?
Asked by Anand, Colchester
Does no one use google and wiki "
A returning boomerang is a rotating wing. It consists of two or more arms, or wings, connected at an angle; each wing is shaped as an airfoil section. Although it is not a requirement that a boomerang be in its traditional shape, it is usually flat.
Boomerangs can be made for right or left handed throwers. The difference between right and left is subtle, the planform is the same but the leading edges of the aerofoil sections are reversed. A right-handed boomerang makes a counter-clockwise, circular flight to the left while a left-handed boomerange flies clockwise to the right. Most sport boomerangs weigh between 70 to 110 grams (2.5 to 3.9 oz), have a wingspan of 250 to 350 millimetres (9.8 to 13.8 in) and have a range on most is between 20 and 40 m (22 and 44 yd).
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wiki/Boomerang Its an aerofoil
Sorry for the noddy post, but need nine posts to put in links
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Does no one use google and wiki?
Not back in 2008 when this question was answered.
Despite Google being founded in 1998, they weren't so totally dominant in search (and advertising) back in 2008.
Despite Wikipedia being founded in 2001, they didn't have the reputation, breadth, depth and editorial standards that have been built up today.
Back then, people would probably have looked up a paper encyclopedia (if they didn't know any university lecturers they could ask)...
- On one occasion, I saw people selling paper encyclopedias in a shopping center. They approached me, but when I asked about the cost of the CDROM version, they totally lost interest. Already they could see that digital media was eating their lunch.
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Does no one use google and wiki?
Not back in 2008 when this question was answered.
Despite Google being founded in 1998, they weren't so totally dominant in search (and advertising) back in 2008.
Despite Wikipedia being founded in 2001, they didn't have the reputation, breadth, depth and editorial standards that have been built up today.
Back then, people would probably have looked up a paper encyclopedia (if they didn't know any university lecturers they could ask)...
- On one occasion, I saw people selling paper encyclopedias in a shopping center. They approached me, but when I asked about the cost of the CDROM version, they totally lost interest. Already they could see that digital media was eating their lunch.
Woops I hadn't noted the date stamp, Colin told me I needed to do some posts so that I could use links.
I do have a friend who claims he made his fortune selling encyclopedias, I suspect he owned the company:)
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Imagine that the two shoulders of a banana-shaped boomerang are its wings. Like the wings of an airplane, their lower surface is flat and the upper one is convex. Such a surface causes the air, which in flight flies around the boomerang, to create lift. The whole secret is that one “wing” of a boomerang is different from the other. The curvature of the curved surface of one wing looks forward, and the other - back. It is like attaching one wing backwards to the plane. You won't envy such an airplane pilot. An airplane, like a boomerang, is organically incapable of flying straight. The shape of the boomerang blades returns it after the flight to the place of throw.
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When I was 12, I found a book in a bookcase in the house called The Boomerang Book. It explained how to make a returning boomerang. I think it must have been bought at the time when my parents were given a boomerang by some Australian relatives/friends (I forget who they were), but that boomerang turned out to be a non-returning killer boomerang which flew in a straight line before digging into the ground. Anyway, having discovered the book, I bought some cheap plywood - rubbish stuff with one thick interior ply and two thin outer layers, and I experimented with that, gradually getting better and better performance out of them. If they hit the ground the wrong way, they snapped, but it didn't matter. I eventually found some decent five-ply and applied what I'd learned to that, and the first one of those that I made was a beauty - in the right conditions (very low wind, but not zero), I would send it out at 45 degrees to the right of the wind (launched held almost vertically and thrown along a path parallel to the ground), but it would tip over to the right (top to the right) as it went along, and this helped it to climb as it turned to the left. It would come back to me from a direction at 45 degrees to the left of the wind, now more and more on its side, and it would flutter down towards me along a fairly straight path, leveling out as it came nearer, sometimes stopping right over my head and hovering there for a moment so that I could reach up and pick it out of the sky. That would be a perfect throw though, and those were rare. Normally I'd have to move a bit to get to the right place.
I haven't seen this old thread before, so it's been interesting (reply #1 in particular). I hadn't considered the connection to what happens with a gyroscope before. When I throw a right-handed boomerang, it heads out at 45 degrees to the right of the wind, and the airfoils are generating lift to the left. The top arm is moving faster through the air, so a stronger force is being generated there, which should tip the boomerang over to the left (meaning top to the left), but that doesn't happen - it gradually tilts the opposite way instead, acting against that extra lift on the top arm, but the whole boomerang also turns to the left, and that's the main reaction. When you apply a force to a gyroscope, it doesn't tip over the way you expect from the way the force is applied, but at 90 degrees to that, and right enough, the extra lift from the upper arm which attempts to tip the boomerang over to the left (top to the left) actually turns the whole boomerang to the left instead while it remains vertical. What I still don't understand is why the tilt to the right gradually increases throughout the flight.
Incidentally, reply #6 seems to be based on the misapprehension that a boomerang is thrown lying flat like helicopter rotorblades. It isn't - it's sent out angled more like the tail rotor.
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They don't. Every time I threw mine the stupid thing just flew away. :-)