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Written by: Gautam Dandavate
Written on: May 2nd, 2003
Tags: entertainment, physics, sports & recreation
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About the Author
At the time of writing, Gautam was a sophomore at USC majoring in mechanical engineering. He is an avid soccer fan and a staunch supporter of Manchester United F.C.
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Volume V Issue III > The Frisbee

Rotation of a Frisbee

Adding spin to a Frisbee while throwing it is crucial in providing it with stability in the air. As just stated, when air flows over the surfaces of the Frisbee, lift is generated and acts vertically upwards. The lift force, however, is not perfectly centered at the middle of the Frisbee. The lift force actually acts on the front part of the Frisbee. Because of this, the Frisbee experiences a torque that tends to flip the Frisbee over about its center. Therefore, a Frisbee that does not have any spin will flip about its center and quickly fall to the ground [5].
However, if spin is applied to Frisbee, a gyroscopic phenomenon known as precession takes place. Precession also accounts for why bicycle wheels and tops are able to stay upright while spinning, but topple over when not. As the spinning Frisbee flies through the air, the non-centered lift force creates a torque that tries to flip it over in the direction shown. However, as the Frisbee rotates to its new position, the lift force now acts at a new point on the Frisbee, and the torque tries to flip over the Frisbee in a new direction. As the Frisbee rotates through 360 degrees, the torques acting at all the different points negate each other, and the Frisbee is able to stay upright without flipping over [7].
Additionally, while a Frisbee spins, "the ridges on the Frisbee's top surface introduce microscopic turbulence into the layer of air" above it, and this turbulence "helps keep the upper airstream attached to the Frisbee, thereby allowing it to travel farther."[5]. Therefore, the ridges on a rotating Frisbee cause the lift force to act on the Frisbee for a longer time, thus extending its range.

Conclusion

The Frisbee started off as nothing more than a container that carried pies for the Frisbie Pie Company. However, through the ingenuity of some college students, the inventiveness of Fred Morrison, and the marketing savvy of the Wham-O Manufacturing Company, it eventually became an immensely popular and internationally recognized toy.
By analyzing the design of this invention, one observes that the Frisbee has a convex upper side, a concave lower side and ridges along the curved surfaces. In the technique of throwing the Frisbee, it is important for it to have an angle of attack and to apply spin in order for the throw to be successful.
By looking at the forces acting on the Frisbee and how they are generated, we can understand their role in determining the Frisbee's flying path. Finally, the rotation of a Frisbee, by means of precession, allows it to stay upright in the air.
Tossing the Frisbee around amongst friends in the park, at the beach or even in the backyard is indeed a fun-filled experience. It is remarkable to think that this enjoyment would not be experienced if it weren't for the complex physical principles at work on this simple toy.

References

    • [1] J. Horowitz and B. Bloom. Frisbee More than a Game of Catch. New York: Leisure Press, 1984, pp. 21, 24.
    • [2] M. Bellis. "The First Flight of the Frisbee." About Inc. Internet:http://inve​ntors.about.com/libr​ary/weekly/aa980218.​htm. [Mar. 17, 2003].
    • [3] E.E. Hedrick "Flying Saucer (Patent Number 03359678)." United States Patent Office. Internet:http://www.​uspto.gov. [Mar. 19, 2003].
    • [4] M. Brain and B. Adkins. "How Airplanes Work." How Stuff Works. Internet: http://travel.howstu​ffworks.com/airplane​.htm. [Mar. 19, 2003].
    • [5] L.A. Bloomfield "The Flight of the Frisbee." Scientific American, pp. 132, Apr. 1999.
    • [6] N. De Mestre. The Mathematics of Projectiles in Sport. Cambridge: Cambridge University Press, 1990, pp. 157.
    • [7] M. Brain and B. Adkins. "How Gyroscopes Work." How Stuff Works. Internet: http:// http://science.howst​uffworks.com/gyrosco​pe2.htm. [Mar. 19, 2003].
    • [8] "How Things Work: Balls, Birdies and Frisbees." The University of Virginia. Internet: http://howthingswork​.virginia.edu/balls_​birdies_and_frisbees​.html, Feb. 22, 2003. [Mar. 19, 2003].