MadSci Network: Physics

Re: I was wondering how a spiral works with a football.

Date: Wed Dec 19 14:14:10 2001
Posted By: Ronald Fisch, Physics, Washington University
Area of science: Physics
ID: 1007229162.Ph

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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