2. The boomerang is moving forward and the boomerang is spinning– creating uneven lift (torque).

When you throw the boomerang correctly, it’s almost vertical when it leaves your hand, not lying flat like a frisbee. The boomerang is both moving forward and spinning, so you’ve got two speeds. As the rotating wing is spinning forward, the rotation speed is added to the forward speed. As the rotating wing is spinning in the opposite direction to the forward motion, the rotation speed is subtracted from the forward speed. See the diagram below:

Greater speed means greater lift. That means, as the spinning boomerang moves forward, more lift is being created on the upper half of the spin than the lower half. This puts a twisting force, or torque, on the spinning boomerang.