Why a boomerang comes back

When you throw the boomerang: 

• It not only spins propeller motion but also flies through the air.
• The wing at the top of the spin moves in the same direction as the forward motion of the throw, while the bottom wing moves in the opposite direction.
• This causes the top wing to move through the air at a higher speed.
• It makes more air pass under it and creates lift because the wing has to exert more force to push down the increased mass.
• It is as if someone is continually pushing the spinning propeller at the top of the spin, causing it to keep turning, travelling in a circle.