Angular momentum vectors and frisbees

[mperkins01]

While working on shooting mechanisms for the 2013 FIRST Robotics Competition, our mentoring scientist noted that the direction of the angular momentum vector pointed down for our prototype shooter. So now we're debating whether the vector points up or down matters for the flight of the frisbee. I argue that it must be the same, since a left handed person can throw as well as a right handed person.

 

[haruspex]

Which way a spin vector points is a matter of convention. See http://en.wikipedia.org/wiki/Right-hand_rule. As far as the maths is concerned, it doesn't matter which way you choose as long as you are consistent. For the flight of a Frisbee or a gyroscope, there are are two spin vectors of interest: its angular momentum and an applied torque. Using the same convention for each of those (and using the convention for direction of cross-product that matches the order in the equation) produces a resultant precession in the same spin convention.

 

[rcgldr]

I argue that it must be the same, since a left handed person can throw as well as a right handed person.

or a right handed person can throw with an "outside" spin to get the same spin as an "inside" left handed throw.

For a frisbee, there's a downwards pitching torque during flight (due to center of lift offset from center of mass) that results in precession to the left or right. An Aerobie, which is a flying ring, is designed to eliminate nearly all of this pitching torque which mostly eliminates the precession issue.