Why boomerangs come back

Illustration for article titled Why boomerangs come back

Here's a guide to the physics of a boomerang's mid-air turn.

If you, like many others, have ever received a boomerang as a present, then you know its remarkable achievement; getting people to buy, throw, and then chase and retrieve sticks. I have never in my life thrown a boomerang in such a way that it came back, nor have I seen anyone else do it. On video – people can do anything with CGI these days. And in the YouTube stuff you can see the string. Nice try, guys.

These people are clearly just trying to go viral. And blurry? That doesn't even work for Bigfoot spotters.


However, physics says that having a boomerang come back once you've thrown it is theoretically possible. It's all due to those two rotating arms. They're joined at an angle of 105-110 degrees, and one side of them is slightly rounded like an airplane's wing.

The correct (And again, I'm only going by the book on this one. Practically speaking there is no correct way to throw a boomerang, just like there's no correct way to prudently invest at a roulette wheel. The only correct thing to do is to not participate.) way to throw a boomerang is to grab it firmly by the lower arm with the ‘point' of the thing looking you in the face. The curved section of the wing should be facing inwards, toward the center of your body, while the flat side should look outwards toward the cold, cruel world. Tilt it outwards at around twenty degrees and throw it hard, making sure to put a good part of your force into throwing it upwards, so it doesn't just embed itself in the ground right in front of you.

If you've thrown it right, the boomerang will spin quickly as it flies. The spin is crucial. Both arms of the boomerang are shaped like the wing of a plane. The curve on the top part of a wing makes air travel faster over it than air travels under it. This means that there's a difference in pressure – the air above the wing loses the shoving match to the air below the wing and the plane moves upwards. A boomerang's wings are flying horizontally instead of vertically. If a boomerang were not spinning, it would just move to the left (Assuming a right-handed throw. Which I am. Suck it, sinister ones.).

When the boomerang spins, things get a little more interesting. The top wing spins into the direction of the throw. The bottom wing spins away from it. As a result, the wing on top always travels faster than the wing on the bottom. You can see this on airport moving sidewalks. Whenever you walk with the direction of the sidewalk, you jet forward. When you walk against the direction (And don't tell me you don't do it. I know you do. We all do.), you walk more slowly.

Because the upper wing is moving forward, it's moving faster in comparison to the air around it, the Bernoulli Effect means it gets a bigger push. The lower wing is movie more slowly with respect to the air around it, it gets a smaller push. The boomerang experiences an overall push to the left at the top of its spin.

This yields two results; one is that the boomerang will get a push that makes it ‘fall over' on its side and rotate horizontally. I'm betting that that would be hard to sell.

The money effect is this. With spinning objects, a push at the ‘top' of the spin will result is an effect ninety degrees further on. Instead of just flopping over, the wheel will twist to the left. Because the boomerang is getting a constant overall push to the left at the top of its spin, it twists to the left. The constant twisting eventually pushes it around in a circle.

Or so I've heard.


Via the Big Site of Amazing Facts, How Stuff Works and the BBC.



James Whitbrook

'Is it a stick, Lord Blackadder?'

'Yes, Ma'am, but it is a very special stick - because when you throw it away, it comes back!'