In 1985 during a mission to rescue the space station Salyut-7, Soviet astronaut Vladimir Dzhanibekov observed something rather strange: a free-flowing wingnut spun around its central axis for a few seconds, and without any force applied, it suddenly flipped 180 degrees to the opposite direction and continued spinning.
He thought of it as a fresh discovery, but little did he know mechanisms of this mysterious movement have been described in classical mechanics for over a century. He was not alone, however. In 1991, a team of U.S. and Netherland researchers also reported what they believed was the first-of-its-kind discovery, about a weird behavior about a twisting tennis racket.
For example, when twisted by its handle or tossed with the net facing sideways, the racket maintains its rotational position until it hits the ground; but when you throw the racket with its net facing up/down, along its intermediate axis, a bizarre thing happens: it turns 180-degree mid-air.
Both phenomena can be explained with the intermediate axis theorem. A solid, symmetrical object such as a tennis racket have three rotational axes — the ones with the maximum or minimum moment of inertia, and the one with intermediate moment of inertia. The theorem suggest that when an object spins exactly around its intermediate axis, the centrifugal force slowly accumulates and destabilizes its position, eventually leading to the object flipping to a position at the opposite direction.
Back to Dzhanibekov's moment of discovery, the Soviet astronaut did not take what he saw as a stroke of serendipity. Because he realized that a potentially apocalyptic consequence might be associated to this phenomenon, therefore keeping it as a secret. Want to find out what triggered Dzhanibekov's fear? Watch the video from Veritasium in full to find out yourself (spoiler alert: it is a-okay after all)
Source: Veritasium via Youtube
