Gyroscopic and aerodynamic forces are responsible for a boomerang faithfully returning. The two arms on a boomerang are shaped a bit like wings on a plane – slightly curved on top and flat underneath. This generates lift as the two arms spin, keeping it in the air, similar to how a helicopter stays aloft.
As a boomerang spins, one arm at any given moment actually moves faster than the other – with respect to the air – as the boomerang continues in its direction of motion. This creates a greater lift force on the arm that spins in the direction of boomerang’s path, resulting in unbalanced forces that gradually change the boomerang’s direction.
Throwing a boomerang horizontally would cause it to curve upwards, where it would fall back down and not return to its starting point. A boomerang should be thrown at an angle between 20-45 degrees right of an imaginary vertical line, for it to have a chance of returning.