# What makes a lasso spin?

Finally, physicists are catching up to cowboys—at least in the lasso department. With the help of a trick roper who works at Disneyland Paris, a custom built “robo-cowboy,” and a researcher who spent hours practicing with a lasso, a team of physicists has mathematically mastered a trick called the flat loop, in which the loop in the lasso rotates horizontally near the roper’s legs. By analyzing high-speed video of both the professional roper and the robo-cowboy (essentially a couple of motorized, rotating joints that mimic the motion of a human arm and wrist) performing the flat loop, the scientists isolated the specific forces that govern the lasso’s movement and wrote the first equations that accurately describe the behavior of the rope during the trick. The key to performing the flat loop like a true cowboy? Making sure you have the right amount of loop in your lasso. About 75% of the total length of the lasso needs to be in the loop for the trick to work properly, the team reports today in the Proceedings of the Royal Society A. Any less and the system will collapse, with the loop shrinking down to a point—a common problem for beginners who tend to make their loops too small. Similar mechanics are seen in industrial yarn processing, the researchers say, although for now they plan to concentrate future work on mathematically describing more complex cowboy tricks.

Posted in: