This basketball dropped with backspin from a dam is equal parts hypnotic and mesmerizing. As the ball falls it gradually curves in mid-air, and then skips several feet on the surface of the water below before coming to a stop.
The people who made the video over at Veritasium explain that the ball curved in free fall due to a phenomenon known as the Magnus Effect.
To demonstrate, they drop a ball from a dam with no backspin. It then essentially falls straight down.
They then drop the ball with a little bit of backspin, and watch as it curves down toward the water, demonstrating the Magnus Effect.
As the ball is dropped and gains speed, air on the front side of the ball is get dragged in the direction of the back spin.
At the same time, air on the other side moves opposite to the way the ball spins, so the flow separates from the ball.
So during the fall, the ball pushes air one way, applying equal force on the ball the other way, causing to shift direction.
They then go on to explain practical applications of the like using cylinders on boats that harness Magnus Effect to increase their efficiency.