Frisbees in Flight
Frisbees have long been used recreationally, but what are the phenomena that allow them to work? What are the physical properties of Frisbees that permit flight? The two fundamental ideas behind the flight of a Frisbee are aerodynamic lift and gyroscopic inertia.
While gravity acts in a downward direction on the disc, the force of aerodynamic lift counteracts gravity. A Frisbee must be thrown with a positive angle of attack, which is the angle formed by tilting the forward part of the disc (side farthest from the thrower's body) upward slightly with respect to the line parallel to the ground. With this positive angle, air travels over the top of the Frisbee at a greater speed than it travels underneath the Frisbee due to differences in concavity. Since the pressure of a fluid (air in this case) decreases as its speed increases by Bernoulli's Principle, there is less pressure on the top of the Frisbee than underneath it. This pressure difference causes the lift of the Frisbee, allowing it to stay in the air.
Maintaining a positive angle of attack allows the Frisbee to force air downward. By the Newton's Third Law of Physics, which states that there is a counteractive force to every action, air reacts to the Frisbee by pushing the disc upward, allowing it to lift.
How does spinning a Frisbee help it to fly? Spinning a Frisbee gives it gyroscopic inertia, also known as Angular Momentum. Since the Angular Momentum is directly proportional to the rotational inertia, or the resistance to changes in rotation and orientation, the Angular Momentum of the spin gives the Frisbee stability while rotating. Thus, the faster a Frisbee spins, the less likely it is to wobble as it flies. These physical phenomena cooperate to allow you to enjoy this recreational toy.