The Magnus Effect

In certain conditions, a ball with spin can curve the opposite direction we’re used to. This happens with baseballs, soccer balls, etc. on Mars (or anywhere else with a thin enough atmosphere) or with a light, smooth ball on earth. In the normal case (when a ball curves as you’d expect), the air that is passing the ball in the same direction that side of the ball is going, the air “sticks” to the ball and is deflected such that the ball curves towards that side of the ball.

For instance, think of a ball with topspin. As it moves forwards, the air passing along the top of the ball will be going against the rotation. This is why balls with topspin drop. The video below is a cool example of the magnus effect.

However, this relies on texture of the ball. In the case of a very light, smooth ball, we can see the opposite behavior. This relies on a laminar flow on the same-direction side and a turbulent flow on the side rotating against the air. As annoying as this girl is, her video has a great description of both the magnus effect and the reverse magnus effect.