A boomerang is basically a gyroscope made of wings and thus is subject to some quirky physics. Specifically, a boomerang benefits from gyroscopic precession, which is the tendency for a spinning mass to wobble when nudged, rather than falling over. Imagine a bicyclist riding no-handed: As she cruises down the street, she stays upright because the bike’s wheels are a pair of gyroscopes, and their spinning gives them stability. If she wants to turn left, she leans left. Now, if this was a stationary wheel, nudging the top of it (as the rider does when she leans) would just knock it over. But since it’s a gyroscope, adding an additional force to the top causes the gyroscope to turn perpendicular to its axis of spin (imagine a top and how it wobbles around its axis instead of just falling over), and the bike magically follows a big leftward looping path.

Since the boomerang is spinning, it’s a gyroscope; this gives it stability in flight. Since the boomerang is a spinning set of wings, forces are acting on it unevenly (just as forces act unevenly on the spinning wheels of the bike when the rider leans). Although the boomerang, as a unit, has a single velocity, each wing has a different velocity relative to that, since the “top” wing is moving forward and the “bottom” moving backward as it spins. Slowly spin your boomerang on your desk while sliding it forward, and you’ll see that the topmost wing is always moving forward and thus is moving a little faster than the unit’s velocity, while the bottom wing is moving backward and thus subtracting its velocity from the velocity of the boomerang as a whole. Identical wings moving at different velocities exert different amounts of force, with the faster wing exerting more force. (This is why an airplane can’t just tool along at 24 mph; you need some hustle to break free of gravity’s ardent embrace.) So, there is a greater force acting on the top of the spinning boomerang than the bottom. This has the same effect as the bike rider leaning left, pulling the boomerang around in a circular path.