|MadSci Network: Physics|
Spinning the football around its long axis prevents the football from tumbling as it travels through the air. The detailed explanation of why this works can be found in any of the standard textbooks on classical mechanics. Without solving the equations of motion, the short answer is that this is a result of conservation of angular momentum. Now, if the football is spinning around its long axis, and the long axis is pointing along the direction of motion, this minimizes the air resistance. So throwing a spiral makes the football travel straighter and further. This idea applies to other types of projectiles, such as bullets. A rifle barrel is grooved on the inside, in order to make the bullet spin around its long axis. And this makes the bullet travel straighter and further, just like the football. On the moon, where there is no air, making the projectile spin would not make any difference.
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