Boomerangs are an important part of Australiana! Famous all over the world, Australia’s first boomerangs date back more than 10,000 years. They were originally used by Indigenous Australian as tools for hunting, fighting, digging and during ceremonies.
If you’ve ever thrown a boomerang then you know exactly why they’re famous. Throw them just the right way, and your boomerang curves its way through the air and comes back to your hands. The only real trick is being able to catch it out of the air!
But how do boomerangs do that? Throw a tennis ball and it flies in a straight line – so why do boomerangs come back?
The Shape of Boomerangs
The shape of boomerangs play a big role in making them come back. The traditional Australian boomerangs most of us are familiar with are a simple curved shape with two arms. These two arms can be almost any size, as long as they have the right shape and are joined together at an angle of about 60 to 80 degrees.
Each arm of a boomerang has the same shape as a plane’s wing (also called an aerofoil). Aerofoil shapes are what allow planes to fly, and they’re part of the reason a boomerang comes back when thrown.
The shape of an aerofoil is like a stretched out oval, but the bottom side is flatter and the top side is more curved. As an aerofoil moves, it splits that air that it’s passing through. The air that travels over the top edge of the aerofoil moves more quickly than the air passing underneath. Fast-moving air has a lower density than the air beneath the wing, allowing the wing to be pushed upwards away from the ground. At the same time, the air that passes underneath the wing is deflected and pushed down. Together with the low-pressure air on top of the wing, these two things create “lift” and allow planes and boomerangs to fly through the air.
How to Throw a Boomerang
So the arms of a boomerang are shaped like aeroplane wings and that allows them to fly – but it doesn’t explain why they come back. Boomerangs come back thanks to a cool bit of physics we’ll discuss later, but it only works if they’re thrown properly.
Throwing a classic two-wing boomerang is simple:
- Use your right hand to hold the boomerang from the bottom at the tip of one of the wings
- The back of the boomerang’s curve should be facing backwards, with the tips of both wings facing forwards
- Hold the boomerang vertically up and down
- Tilt your arm to the right until you are holding the boomerang at about a 20 degree angle from vertical
- Take a step and throw the boomerang forwards
- As you swing your arm to throw, bend your wrist with a snapping motion to make the boomerang spin as it flies
When thrown properly, a boomerang has two different motions going on. The first is forward motion from the throw (just like if you threw a tennis ball). The second is the spin. Because the boomerang is moving forwards and spinning at the same time, the two wings are actually moving at different speeds. The wing on top moves faster than the one on the bottom, meaning the top wing generates more lift and causes the boomerang to tilt as it flies.
Boomerangs and Gyroscopic Precession
We mentioned it above, but boomerangs come back thanks to an interesting bit of physics called “gyroscopic precession.”
Gyroscopic precession is a force generated by spinning objects such as bicycle wheels. If we imagine a spinning bike wheel that’s suspended from the ceiling, the wheel would be generating a force called “torque” along the length of the axle. That torque and the weight of the wheel cause the wheel to rotate around its vertical axis, and that rotation is what we’d call gyroscopic precession.
This effect is easiest to understand with a demonstration:
https://www.youtube.com/watch?v=ty9QSiVC2g0
Boomerangs work the same way as the suspended bike wheel. The lift generated by the aerofoil shape of the wings tilts the boomerang as it flies, and the gyroscopic precession causes the boomerang to rotate. Together, these two things make the boomerang fly in a circle.
Want to Know More About the Forces of Flight? Book an Incursion with Street Science!
Boomerangs date back more than 20,000 years, but they’re actually a pretty complicated bit of physics. While Indigenous Australians often used them for hunting, modern boomerangs are a lot more fun when they’re used as toys. Understanding how objects fly can be a bit complicated, but Street Science has put together a range of science incursions to help students grasp the physics behind flight. Our school incursions are built to work alongside the Australian school curriculum, and our experienced instructors know how to deliver lessons that are fun and engaging! Contact us to find out more about our programs or if you’d like to book a school incursion with us today!
