Two key ingredients to their
long flight times are their lift generation and spin. A frisbee in flight
behaves very much like a wing, generating lift by flying at an angle of attack.
This angle of attack and the curvature of the disk rim cause air to accelerate
over the top of the leading edge. Airflow over the top of the disk is faster
than that across the bottom; thus, pressure is lower over the top of the
frisbee and lift is generated.
Aerodynamic lift and drag aren’t enough to keep the frisbee aloft long, though. Spin matters, too. If the frisbee is launched without spin, gravity acts on it through its center of mass, but lift and drag act through a point off-center because lift tends to be higher on the front of the disk than the back. This offset between gravitational forces and aerodynamic forces creates a torque that tends to flip the frisbee.
By spinning the frisbee, the thrower gives it a high angular momentum acting about its spin axis. Now instead of flipping the disk, the torque caused by the offset forces just tips the angular momentum vector slightly. Physically, this is known as spin stabilization or gyroscopic stability. Tomorrow we’ll take a closer look at airflow over the frisbee.
Aerodynamic lift and drag aren’t enough to keep the frisbee aloft long, though. Spin matters, too. If the frisbee is launched without spin, gravity acts on it through its center of mass, but lift and drag act through a point off-center because lift tends to be higher on the front of the disk than the back. This offset between gravitational forces and aerodynamic forces creates a torque that tends to flip the frisbee.
By spinning the frisbee, the thrower gives it a high angular momentum acting about its spin axis. Now instead of flipping the disk, the torque caused by the offset forces just tips the angular momentum vector slightly. Physically, this is known as spin stabilization or gyroscopic stability. Tomorrow we’ll take a closer look at airflow over the frisbee.
( Image credit: A. Leibel
and C. Pugh, source video: Frisbee Toy Box Physics ; recommended
papers by: V. Morrison: https://stuff.mit.edu/afs/sipb/user/kolya/afs/root.afs/athena.mit.edu/activity/w/womens-ult/www/smite/frisbee_physics.pdf and R.Lorentz:http://www.lpl.arizona.edu/~rlorenz/frisbeenewscientist.pdf )
rich pollett
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