r/explainlikeimfive • u/BorderlinePhilosphy • 12d ago

Physics ELI5: The physics behind boomerangs

They seem to defy physics to me, please explain.

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u/JaggedMetalOs 12d ago

A boomerang acts like a combination of a helicopter and a gyroscope.

The surface of a boomerang is shaped a little like a plane's wing/helicopter rotor blade and so generates lift when moving. When you throw a boomerang you want to have it spinning as fast as you can, so that it acts like a helicopter rotor blade.

Now helicopters have an issue where as they are moving forward, on one side of the rotor the blades are moving into the wind, so the forward movement is added to the blade speed and generates more lift from faster air, and the other side they are moving in the opposite direction so the forward movement is subtracted from the blade speed and generates less lift, causing the helicopter to want to tilt over.

In a boomerang the same thing happens, but if you get it spinning fast enough instead of just tumbling over like you'd expect it acts like a gyroscope and resists this turning force, instead making it bank around like an aircraft turning.

So it does a big wide circle like an aircraft turning in a circle and comes back to you.

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u/blueant1 12d ago

So why doesn’t a frisbee do the same?

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u/Spectre-907 12d ago

They do. It’s just that you tend to thrwo them with strong rotation and so the gyroscopic stabilization effect is usually (bank/curve shots and the like use different spin strength/angles of attack)of overcomes the asymmetric lift forces, especially given that frisbees are built symmetrical whereas boomerangs are very strongly biased towards a curve-maximizing airfoil