The Come Back When you throw a boomerang, it is different than the motion of a helicopter propeller, or a plane wing because it does not start from a stationary place, but it is moving through the air while it rotates.  As the boomerang fly's through the air, it has two different velocities.  the angular velocity symbolized by the yellow arrows in the picture below, which correlates to the rotating motion of the boomerang. It also has linear velocity, which is the one we are all familiar with that has no rotation, shown by the blue arrow.   (2) http://www.itworld.com/sites/default/files/BoomerangPhysics590.jpg At the top of the boomerang, angular velocity and linear velocity are in the same direction.  So at the top of the boomerang it is accelerating faster than the rest of the object.  At the bottom , the angular velocity is moving in the opposite direction as the linear velocity.  So at the bottom of boomerang, velocity is the slowest!  Where the velocity increases,  more air is going to pass underneath it creating more lift, just like the picture on the previous page shows.(2) Now here comes the tricky part.  When you push on something that is rotating in a circular motion, you wouldn't necessarily guess what happens next.  Say you push on a  wheel that is rolling down a hill.  You would think that it would fall in the direction you push like any other object.  But in-fact, the wheel reacts to the pushing force at a 90 degree angle.  This happens because you applied the force at the top of the wheel, not anywhere else.  As the wheel rotates around, the force is still felt at that exact point you pushed, it has just rotated around the tire.  After pushing the tire though, it would quickly straighten out because of the force rotating all around the tire, counter-balancing it.  But if you were to keep applying this force, it would continue in that direction until the force was let off. (2)  Just like a boomerang, the force of the air pushing on the two different components doesn't just keep the boomerang in the air, but moves it ~ 90 degrees from the force applied until it makes a complete rotation back to the person who threw it!                                                                                                                                                                      http://www.4physics.com/phy_demo/boomerang/boomerang-torque.jpg                                                                                                                                                                                                                                      www.4physics.com