The trick to controlling the notched stick’s rotation

The notched stick is a simple toy based on complex scientific principles. It has fascinated players and physicists for years. The player holds the notched stick in one hand and runs a small excitation bar over the notches, causing a propeller attached to the end of the stick to rotate. Interestingly, the direction of rotation of the propeller can be controlled by holding the excitation bar in distinct ways.

As a child, author Martin Luttmann was intrigued by his father performing the magic trick of the notched stick. Many years later the two physicists collaborated to investigate its working principles. Unlike previous works, they focused on the origin of the movement of the nail that attaches the propeller to the stick, which illuminates the directional control of the propeller’s rotation.

“The secret lies in the way you hold the bar that rubs the notched stick: by pressing on either side of the stick, you disrupt the trajectory of the nail and make it turn in a controllable direction,” said Luttmann. “What’s fascinating is that the device works so well in practice! There is no need to precisely control the parameters — our work provides explanations for this fact.”

They demonstrated this by using an idealized model of the notched stick. The authors fixed the toy on a panel and magnified its oscillations using a laser beam reflected on a mirror. A stretched rubber band models the perturbation force.

Besides satisfying the curiosity of players, the authors note that the principles of the notched stick can inspire practical applications in other fields.

“The concepts presented here could be used to limit, or generate, vibration-induced rotations in other physical systems,” said Luttmann.

Source: “A story with twists and turns: How to control the rotation of the notched stick,” by Martin Luttmann and Michel Luttmann, American Journal of Physics (2025). The article can be accessed at https://doi.org/10.1119/5.0225847 .