system
Given the following post, respond as if you're commenting on Reddit:
human
Why does a boomerang come back?
gpt
A boomerang works the same way an airplane wing does.  One side is flat, the "outside" as viewed in its flight curve.  The other side has an curved shape, this is usually done down each leg in a shape called an airfoil.  As the air moves over the airfoil, a low pressure is established over the airfoil, pulling the boomerang in flight.  As it moves forward, this creates lift, but because it is thrown upright, instead of going up, the lift is in a sideways direction.  Over most of the flight path, this creates a right to left curve for right handed throwers, and a left to right curve for left handed throwers. (Left handed boomerangs are constructed slightly differently).

Many boomerangs used by aborigines in Australia were not designed to come back to the thrower.  Inland, they were shaped more like clubs.  They could actually skip along the ground and stun prey.  They did curve in flight, which is pretty smart because the target may be looking more at the hunter than a sharp edged stick flying in from their side.  Boomerangs that returned were used more in coastal areas where they were used to drive birds towards the hunter on its return flight.