That's a splendid little video, and an elegant demonstration of spin conservation. I urge people to see it.
The air particles and spin both rotate 90 degrees as a result of the collision. Fascinating! It would be interesting to see how this works in a low pressure cell, close to vacuum. I wonder if it would resemble the computer simulations of colliding galaxies, in which the stars fly out in all directions, presumably because individual particle interactions (particles being stars in this case) predominate. Not at all like the ordered behavior of the air molecules in this video. Maybe the disordered effect I am thinking of could only be achieved with a noble gas at low pressure. - Jed
