Assuming low wind velocity (say, below 5 km/h) do sports balls such as soccer balls and baseballs really curve horizontally (laterally) in mid-flight? Or is it just a visual illusion?
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Yes, it's the result of the Magnus force.
Around every object in air (or other fluid) is a boundary layer. You can think of this as being a thin layer of air that is attached to the object. When a ball spins and moves through the air, this boundary layer detaches and alters the flow of air around the object. What you find is that this change in flow causes a force laterally and the ball curves.
Professional pitchers in baseball can curve the ball up and down, and sideways depending on their grip and the spin they apply.
Have a look at:
http://www.youtube.com/watch?v=6Bvz9jQHy…
to see this force in action in soccer.
Around every object in air (or other fluid) is a boundary layer. You can think of this as being a thin layer of air that is attached to the object. When a ball spins and moves through the air, this boundary layer detaches and alters the flow of air around the object. What you find is that this change in flow causes a force laterally and the ball curves.
Professional pitchers in baseball can curve the ball up and down, and sideways depending on their grip and the spin they apply.
Have a look at:
http://www.youtube.com/watch?v=6Bvz9jQHy…
to see this force in action in soccer.
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Although they don't turn sharp corners, soccer balls, baseballs, volleyballs, golf balls, and other sports balls can follow a curved path, even with no wind. The irregular surface of the ball and its spin can interact with air-resistance and cause it to break significantly.