Centripetal forces, gyroscopic precession (change in the direction of the axis of an object when torque is applied) and the aerodynamic arms of the boomerang act to return the boomerang back to you.

Like an airplane wing, the top of a boomerang is curved, while the bottom is flat. This design lets air move more quickly over the top of the boomerang than over the bottom. Since there is more air pressing on the bottom of the boomerang, the air pressure provides lift to the boomerang.

A properly thrown boomerang leaves your hand spinning almost vertically. As the front arm of the boomerang cuts through the air, it leaves a trail of turbulence behind it, which the second arm has to go through. The turbulence of the first arm makes the following arm go slower. The boomerang is now moving faster at the top of the spin than the bottom. Because of the difference in speed, more lift is given to the top than the bottom of the boomerang.

Now gyroscopic precession intercedes: any force applied on an object rotating around a central point, like a top (or boomerang) will affect the object 90° from where the force was applied. The force of the throw is forward. The top of the boomerang is moving faster than the bottom, so the pressure affects the top more.

Since the top has more force acting upon it, the gyroscopic precession tips the top to the right, and the boomerang spins around to the left in a circle. The boomerang rises as the air rushes over the flat bottom and the rounded top.

Centripetal forces make the boomerang increase in speed, and the boomerang levels off as the centripetal force pushes on the angled top half. The boomerang is now almost horizontal, and close to finishing the circular turn. Gyroscopic precession barely affects the boomerang since the boomerang is horizontal, so the boomerang goes into a straight line.

As the boomerang climbs, energy is lost and the air pressure on the bottom of the boomerang decreases. The boomerang begins to loose altitude. The energy increases once again as the boomerang looses height, and it speeds up. The increase of energy gives lift to the wings. The boomerang slows and loses altitude continuously as it comes to hover slowly down into your waiting hand.

Boomerang fun facts:

• There are two types of boomerangs: Non-returning (war/hunting) and Returning (sport/toy).
   
• Returning boomerangs were used in sport or as a toy. A competitor’s skill is tested by the precision of the return and the speed and quality of the flight. Also, children would use the boomerang as a toy. They would try to see who could get the boomerang to return nearest to a peg or marker that was set into the ground.
   
• Kylie is the name for the non-returning or hunting boomerang. Also referred to as a throwing stick.
   
• The angle of the boomerang’s curve is typically between 70° and 120°; and the most common angle is around 90°. The theoretically ideal angle is 109°. Most boomerangs are within 20° of this degree.
   
• On average the wingspan of the boomerang is between 30-60 cm.
   
• On average, boomerangs weigh between 30-180 grams, or around 8 ounces.
   
• Suggested by the Judge Advocate of Port Jackson in 1778, the word “boomerang” came from the Aborigine word wo-mur-rang. In another part of Australia, the George’s River aborigines called the boomerang the bumarin. In 1827, Capt. King combined the two terms to form the word “boomerang”.

Further Reading

Blanding, Sharon L. What makes a boomerang come back. In What makes a boomerang come back: how things in sports work. Stamford, CT, Longmeadow Press, c1992. p. 58-67. Boomerang. In How products are made: an illustrated guide to product manufacturing. v. 6. Edited by Jacqueline L. Longe. Detroit, Gale Group, 2001. p. 54-58. Can also be accessed online: http://www.madehow.com/Volume-6/Boomerang.html Hawes, Lorin L and Mary Hawes. All about boomerangs. New York, Paul Hamlyn Pty Ltd, 1975. 72 p. Smith, Herb A. Boomerangs: making them and throwing them. Littlehampton, United Kingdom, Gemstar Publications, 1975. 34 p. Sagert, Kelly Boyer. About boomerangs: America’s silent sport. Northridge, OH, Plant Speak Publications, c1996. 121 p. Ruhe, Benjamin and Eric Darnell. Boomerang: how to throw, catch and make it. New York, Workman Publisher, c1985. 93 p.. Ruhe, Benjamin. Many happy returns: the art and sport of boomeranging. New York, Viking Press, 1977. 105 p.