The Science Behind Boomerangs

The creation of boomerangs likely resulted from a process of experimentation. Explore the theories experts propose about their origins.

For many, the word boomerang conjures images of a banana-shaped stick being thrown, only to curve back to the thrower—perhaps after humorously bonking someone on the head. As kids, we often believed such a device must be enchanted. In reality, the inventors of the boomerang didn’t stumble upon magic but rather harnessed the intricate principles of physics to create something extraordinary.

This article explores the scientific principles behind boomerangs, examining their flight dynamics and the correct technique to throw them so they return. We’ll also touch on their historical origins, showcasing how boomerangs are both a fascinating application of physics and an enjoyable solo sport.

Boomerangs are typically known for their curved design that allows them to return when thrown. However, there are two main types: returning boomerangs, made from lightweight materials like wood or plastic, and other modern designs with multiple wings. These are usually 1 to 2 feet (30 to 60 cm) in size, though variations exist. When thrown properly, they follow a circular path and return to the thrower.

Returning boomerangs are not practical for hunting due to their difficulty in aiming. Striking a target would prevent them from returning, which contradicts their intended design.

Returning boomerangs originated from non-returning boomerangs, which are heavier, longer (often over 3 feet or 1 meter), and lack the aerodynamic features that enable return flight. These were effective as hunting weapons due to their accuracy and speed. Additionally, battle boomerangs were used in close combat, serving as non-returning weapons.

Why Does It Fly?

When you throw a straight piece of wood similar in size to a boomerang, it will travel in one direction, flipping end over end, until gravity brings it down. The key question is: How does altering its shape allow it to stay airborne longer and return to the thrower?

What sets a boomerang apart from a plain stick is its multi-part design, unlike a straight piece of wood, which is a single unit. This design enables the boomerang to rotate around a central point, stabilizing its flight. Non-returning boomerangs outperform straight sticks as throwing weapons due to this stability, offering greater distance and precision.

Returning boomerangs feature unique components that distinguish them from simple curved sticks. A traditional banana-shaped boomerang is essentially two wings connected as one unit, which is crucial for its unique flight pattern.

The wings are slightly tilted and designed with an airfoil shape—rounded on one side and flat on the other, similar to an airplane wing. As explained in How Airplanes Work, this design generates lift. Air moves faster over the top of the wing than underneath, creating a pressure difference. This results in greater pressure below the wing, producing lift as it moves.

As illustrated in the diagram, the two wings are positioned so their leading edges face the same direction, much like a propeller. Essentially, a boomerang is a free-moving propeller. Propellers, such as those on airplanes or helicopters, generate forward motion by spinning their blade-like wings through the air. This force acts on the axis, the central point of the propeller. Vehicles like planes or helicopters are propelled by attaching them to this axis.

The axis of a classic boomerang's propeller is imaginary, so it isn’t attached to anything. Instead, the propeller moves due to the lift generated by the wings. One might assume the boomerang would fly straight in one direction as it spins, similar to a plane with a spinning propeller. If thrown horizontally, like a Frisbee, you might expect it to rise upward, following the direction of the axis, until gravity takes over. If thrown vertically, the correct method, it might seem it would fly sideways. However, this isn’t what occurs.

In the following section, we’ll explore why a boomerang curves and returns to the thrower.

Why Does It Come Back?

Unlike the propellers of airplanes or helicopters, which begin spinning while the vehicle is stationary, a boomerang is thrown, combining its spinning motion with forward flight through the air.

As shown in the diagram below, the wing at the top of the spin moves in the same direction as the throw’s forward motion, while the wing at the bottom moves in the opposite direction. This means the top wing, though spinning at the same speed as the bottom wing, travels through the air faster.

When a wing moves faster through the air, more air flows beneath it, generating greater lift as the wing exerts more force to displace the increased air mass. This effect is akin to constantly pushing the top of the boomerang’s spinning propeller.

However, pushing something from the top, like a chair, typically causes it to tip over. Why doesn’t this happen when force is applied to the top of a spinning boomerang?

If you’ve read How Gyroscopes Work, you might already understand the principle at play. When force is applied to a spinning object—such as a wheel, airplane propeller, or boomerang—the reaction isn’t straightforward. For example, pushing a spinning bicycle wheel at the top causes it to turn left or right, as if the force were applied to the front. This occurs because the point of application isn’t fixed; it rotates around an axis. The force has its strongest effect about 90 degrees off from where it was initially applied, creating a delayed reaction.

In this case, the wheel would briefly turn and then straighten out because the point of force rotates around it, applying force on opposite sides and balancing the effect. However, continuously pushing the top of the wheel would maintain a steady force on its front. This force would outweigh the counterbalancing forces, causing the wheel to keep turning in a circular path.

If you’ve ever ridden a bicycle without using the handlebars, you’ve felt this phenomenon. Shifting your weight causes the top of the wheel to move sideways, but instead of tipping over, the bike turns left or right, unlike when it’s stationary.

The same principle applies to a boomerang. The uneven force from the speed difference between its wings creates a constant force at the top of the spin, which is felt on the leading side. Like a leaning bicycle wheel, the boomerang continuously turns left or right, following a circular path back to its starting point.

How Do I Throw One?

As we’ve explored, multiple forces act on a boomerang as it spins through the air. These include:

There are five key factors influencing a boomerang’s flight. For it to complete a circular path and return to the starting point, these forces must be perfectly balanced. Achieving this requires a well-crafted boomerang and proper throwing technique. While cartoons make it seem effortless, real-life boomerang throwing demands practice and skill. In this section, we’ll cover the basics to help you refine your throw.

Your initial throws will likely fall short, so start with an inexpensive plastic boomerang rather than a costly hand-carved one. Mastering boomerang throwing takes time and practice, but it’s a rewarding and enjoyable skill. The thrill of successfully catching a returning boomerang is unmatched!

How Was It Invented?

While the physics behind boomerangs becomes clear once understood, it’s unlikely early humans stumbled upon this concept spontaneously. So, how did this remarkable invention emerge? Anthropologists suggest it was largely a process of trial and error.

First, consider how a primitive hunter might have developed a non-returning boomerang. Early humans used rocks and sticks as basic tools, with the club being one of the earliest inventions—a simple stick for striking. Throwing a club to hit a target was a natural progression, making it plausible that this was a common practice.

Naturally curved sticks, resembling boomerangs, were likely thrown frequently. The two branches of such sticks provided stability, allowing them to stay airborne longer and travel more accurately. Observing this, early humans began selecting bent sticks for throwing, eventually refining them for hunting. Non-returning boomerangs have been discovered globally, with the oldest, found in Poland, dating back approximately 20,000 years.

The exact origin of returning boomerangs remains unclear, but the Aborigines of Australia are widely credited with their invention. They used non-returning boomerangs, or kylies, for hunting. It’s theorized that an Aboriginal hunter, inspired by the V-shaped wings of soaring birds, may have crafted a smaller, more angled kylie, leading to the discovery of its arcing flight.

The unique flight pattern of this new discovery didn’t enhance hunting accuracy—in fact, it made aiming more challenging—but it was undeniably fascinating. Over time, the Aborigines refined the boomerang’s design and throwing technique primarily for enjoyment, transforming it into a sports tool. The classic game involves throwing the boomerang as far as possible while still catching it on its return. While its hunting use was limited, the Aborigines cleverly employed boomerangs to scare birds into nets by mimicking hawk calls.

The boomerang stands as humanity’s first flying device, paving the way for inventions like the airplane, helicopter, blimp, and even the space shuttle. It’s astonishing how a simple piece of wood harnesses complex physics so effectively—so much so that it appears magical until the science is understood. As both a physics teaching tool and one of history’s most extraordinary toys, the boomerang remains a marvel.