Originally Posted by Parker1287

My guess:

A boomerang's shape is similar to a plane's wing: an airfoil

As you know, an airfoil is shaped such that air travels faster over the foil than below it. This generates a high pressure system below the foil (due to relatively slow air movement) and a low pressure system above the foil (due to relatively fast air movement). The result is a net force pointing from the bottom of the foil to the top. I won't say "up" because if the foil is upside down then the net force is pointing down.

If a constant force is applied to an object, it will accelerate at a constant rate (Newton's second law). Therefore, the foil will constantly accelerate in the direction of its top side. If gravity were not present, then planes would constantly accelerate into the sky.

A boomerang is thrown at approximately a 45 degree angle, the reason for this is the following: If it were thrown at a 90 degree angle (vertically), then it would have lift only in the horizontal direction and would plummet to the ground with an acceleration of 9.8m/s^2. If it were thrown at a 0 degree angle (horizontal), it would have lift only in the vertical direction and rise up into the air, but never return to the thrower. A 45 degree angle provides a lift force in both the horizontal and vertical axis, allowing the boomerang to maintain its altitude while also accelerating in the horizontal direction (Note: circular motion at a constant angular velocity does not mean the object has a constant velocity, it is constantly accelerating towards the center of its circular path). My guess is that this horizontal lift force is how the boomerang is able to return to the thrower. However, I have no idea what mechanics induce a change in the pitch (the nose of an aircraft raising or lowering) which allows that force to point to the center of a circular path. Based on my explanation, the boomerang would point in the same direction the whole time and simply accelerate to the left (for a right handed thrower)

All a guess though