Publication by Laboratoire de physique in Physical Review Letters on October 4, 2019.
Friction with the air allows a rapidly rotating loop of string to lift up its unsupported end.
Experiments with a loop of string pulled rapidly through rollers show that the free end lifts up, rather than hanging vertically, thanks to a boost from air friction. Nicolas Taberlet and his colleagues at the University of Lyon in France found that two main factors determine the motion –the weight of the material and the drag force on the loop as it moves through the air. The drag force allows the rotating loop to “push” against the air and rise upward. Experiments in a vacuum chamber proved the importance of the drag force– in the absence of air, a rotating string loop remains vertical. [...]