Fun with Physics, Starring the Flying Disc

You don't have to understand the physics of the flying disc to throw a great "hammer," but it certainly doesn't hurt.

At least that's the case with Peter Delamere, a Geophysical Institute graduate student who's one of the best flying disc flingers in Fairbanks. He hurls backhands, forehands, and the hammer, an overhead release that travels quite a distance upside-down before dropping like a lead sinker into the stinging hands of a receiver.

Delamere, who studies space physics at the Geophysical Institute, is one of a half dozen other G.I. grad students who play Ultimate, a game like football or soccer except players sling a flying disc instead of a ball.

Applying a spin is crucial to the flight of a flying disc (which I would call a "Frisbee" if that word wasn't a trademark of Wham-O). Delamere demonstrated this fact by pushing his 175-gram flying disc through the air as if he was tossing a shot put. The non-rotating disc fluttered to the ground like an overyellow birch leaf.

As Michael Gold pointed out in the essay "The Fairy Tale Physics of Frisbees," a flying disc can be considered a combination gyroscope and airplane wing. A gyroscope is a spinning mass that tends to be stable because of that spin. The faster an object spins and the heavier it is at the outer edges (where most of the weight in a flying disc is), the more steadily it holds its course.

The airplane wing analogy comes from the flying disc's ability to push down a column of air as it's thrown with the forward lip tilted up. Any flat object moving with this slight "angle of attack" will push air toward the ground. As the air is forced down, an equal but opposite force is exerted on the bottom of the disc, and that's what keeps it afloat. Because discs are flat on both sides, the lifting force works even when the disc is inverted, enabling such creative throws as the hammer.

Sometimes, however, a botched throw-one released with the front lip of the disc lower than the hand-seems to miraculously recover. When a person releases a disc within a few degrees of what's known as the Hyzer Angle, the disc will nose up and gain stable flight, Gold wrote. If the Hyzer Angle is exceeded, the disc bites the turf.

In his article, Gold explores the morphology of the flying disc. The concentric ridges that make a disc harder to pull from a Labrador retriever's mouth are known as Lines of Headrick, a feature added by Wham-O after the toy company bought the rights to Morrison's Pluto Platter in 1957. The lines were named for Ed Headrick, Wham-O's former vice-president and head of research. The purpose of the raised ridges is to fight disc-slowing suction sometimes caused when air flowing over the disc suddenly breaks over the outer edges, leaving a low-pressure pocket trailing behind. The Lines of Headrick were designed to work like small tabs on aircraft wings called vortex generators, but the Lines have never been scientifically proven to work, Gold wrote.

Whether the Lines of Headrick reduce drag or not, a flying disc can really move. They've been thrown over 500 feet; tosses have danced on the air for over 15 seconds; and people have chucked discs at over 70 miles-per-hour. Ouch. I think I'd rather catch one of Delamere's hammers.