Key concepts
Aerodynamics
Forces
Physics
Lift
Drag

Introduction
Are you good at tossing a Frisbee? Have you ever wondered how a Frisbee is able to fly through the air so well? If you can throw a perfect, arcing curve right on target, you've already trained your arm to aid in the aerodynamics of Frisbee flight! In this activity, you'll investigate how the angle at which you throw the Frisbee affects its flight direction and distance. Next time you're out tossing a Frisbee, this little lesson in aerodynamics may help make your throws even more accurate!

Background
Two key forces that act on a Frisbee during flight are lift and drag. Lift is the force that allows the Frisbee to stay airborne, and in flight it opposes the force of gravity on the disk's mass. The Frisbee itself creates this lift force as it flies through the air. Because of the Frisbee's curved shape, the airflow above it must travel at a higher velocity than that underneath, thereby creating low pressure above and high pressure below the disk. This pressure difference provides the lift. Drag is a resistant force on the Frisbee, perpendicular to the lift, and it acts against the disk's movement through the air. The angle at which the Frisbee is thrown, which we'll call the "launch angle" (aka the angle of attack), affects both lift and drag.

As a side note, you've probably noticed that a Frisbee doesn't travel far if it's thrown without spin. Spinning the Frisbee helps it fly by supplying angular momentum, which helps keep the Frisbee stable; the faster it spins, the more stable it should be.

Materials
•     A Frisbee
•     Long string or hose
•     Large open area in which to toss a Frisbee
•     Tape measure
•     A helper (optional)
•     A piece of paper and a pen or pencil (optional)

Preparation
•     Use the long string or hose to make a long, straight line in front of you, at least 7.5 meters long. You will be throwing the Frisbee so that it is directed down this center line.
•     Practice throwing the Frisbee down the straight line a few times so you get used to tossing it. If you have not thrown a Frisbee much before, you may want to try practicing it for a little while. Tip: A good way to throw a Frisbee is by standing sideways with the Frisbee held in front of you (near your non-tossing shoulder), then bringing the disk horizontally across you before you release it.
•     If there is wind during any of your Frisbee throws, note the wind speed and direction.

Procedure
•     Throw the Frisbee as flat and horizontal as you can, aiming it down the center line you made. You can have a helper watch to confirm the angle at which you throw the Frisbee. How far did it travel? How far did it veer from the center line, and in what direction (left or right)? If you have a piece of paper and a pencil or pen, you can record this data and all following flight information.
•     Throw the Frisbee as flat and horizontal as you can at least four more times. Each time throw the Frisbee with similar arm motion and speed, use a similar spin, and have the same release point. How far did the Frisbee travel each time? How far did it travel away from the center line, and in what direction?
•     Throw the Frisbee tilted up a little, at a roughly 45-degree angle above the previous, flat throw. (You can imagine that if your arm were the hour hand of a clock, the previous throw would have been directed toward three o'clock and this throw should aim between one o'clock and two o'clock). Throw it this way at least five times. Other than changing the launch angle, try to keep all other aspects of the flights the same. How far did the Frisbee travel each time when thrown at an upward angle? How far did it travel away from the center line, and in what direction?
•     Throw the Frisbee tilted down a little, aiming at an angle about 45 degrees below a flat throw (between four o'clock and five o'clock), at least five times. Again, try to keep all other aspects of each flight the same. How far did the Frisbee travel each time when thrown at a downward angle? How far did it travel away from the center line, and in what direction?
•     Did you see a consistent relationship between launch angle and flight direction? Is there a relationship between launch angle and distance? Based on aerodynamic principles, why do you think you saw these relationships?
•     Extra: In this activity, you investigated how the Frisbee's launch angle affects its flight distance and direction, but you only tested a few angles. You can try this activity again but test even more angles, such as angles in between the ones you tried in this activity. You can videotape your throws and then watch the video to analyze and confirm the angles at which you threw the Frisbee. How well does the Frisbee fly using other launch angles? Is there an angle that consistently correlates with the "best" flight in terms of distance and stability?
•     Extra: In this activity there was not a focus on the effects of wind on a Frisbee's trajectory, but it can definitely be a factor. How will the Frisbee's flight be affected by throwing it into the wind? What about across or with the wind? How does the launch angle change a flight in each of these conditions?
•     Extra: You could compare the flight of a Frisbee with that of an aerobie (flying ring disk). What differences do you notice? Can you explain them in terms of aerodynamic forces?

2 Comments

1. 1. yglick 07:53 AM 8/14/12

   The explanation for lift ("airflow above it must travel at a higher velocity than that underneath...") is simply not right, though used over years to explain a plane's lift.
   The fact is that a perfectly flat , thin disk will fly. Not as efficiently as a frisbee, but fly nevertheless.
   The truth is very simple: The frisbee (or wing) causes the air flow to have a downward component on the trailing edge. Because the leading edge 'sees' still air, there is a net downward momentum (of the mass of air) and following the laws of preservation of momentum, there must be an upward momentum to exactly compensate. Walla! that's the lift. Simple.

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2. 2. Raoul 12:56 AM 8/24/12

   I think blue arrows of the image are not correctly settled ; the one for lift should be vertical and the other should be in the direction of the heading.

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