The ability of boomerangs to fly and return is based on simple physics and aerodynamics. A boomerang gains its lift from the way it is thrown. Although the boomerang spins and travels at constant rates, the wing on top moves faster through the air than the bottom wing. More air moves under the higher wing, causing it to move up. The circular flight path is caused by both the crooked wing design and again, the spin. The wing on the top is always tilted in the direction it is turning, no matter which wing it is. This is combined with effects similar to that of a bicycle tire. When a force is applied to the top of the tire to either side, the tire will not react until it has done a quarter revolution. At this point, the force is effectively applied, and the tire will turn in response to the force, not tip over. The same thing happens with boomerangs. The difference in air speed between the two wings creates a force on the top wing of the boomerang, and the tilted wing determines which way it will turn. The constant force and turning causes the boomerang to loop around and come back.