by Laundon Transue, PA-S

Have you ever played disc golf? Maybe you know someone who has. Or maybe you’ve seen it from a distance. Perhaps you were taking a walk through a park or on a hiking trail and noticed a warning sign: “You Are Now Entering a Disc Golf Course – Watch Out for Flying Discs.” It can be a dangerous sport.

It’s just like golf, but with frisbees. Only instead of putting your ball into a hole in the ground, you throw your disc into an odd looking metal basket situated on top of a pole with a bunch of chains hanging from it. Maybe you’ve seen one such basket on your stroll through the park and thought “What is that thing?” That’s disc golf.

I learned to play this game in the forests and hills of Northern California, close to sea-level. Colorado is home to some of the best disc golf courses in the country, so I was excited to venture out and experience them after moving here. However, I could tell immediately that something was wrong the first time I played a round in Summit County – my discs were not flying like they used to!

How exactly were they flying differently? It was hard to say, I just knew they weren’t flying like I was expecting them to. It was throwing my game off. I’ve learned quickly that life at over 9,000 ft has all sorts of challenges not faced by sea-level dwellers. After a few rounds of disc golf up here and feeling like I had to learn how to play all over again, I wondered if my new high altitude environment had something to do with why my discs were misbehaving.

I set out to better understand the physics behind how discs fly through the air and how altitude affects these characteristics.

A lightweight flying disc traveling through the air is very sensitive to the atmosphere. At sea-level there is increased air density, so flying objects encounter more air resistance. As elevation increases, air density decreases, and there is less resistance in the air for flying objects to encounter. So yes, high altitude does cause flying objects to fly differently, but there’s a lot more to the story when it comes to disc golf.

Disc golf is a challenging game. The goal is to throw a ⅓ lb plastic disc hundreds of feet through the air across rough terrain while avoiding trees, hills, ponds, and eventually land in that odd metal basket, hopefully doing so in fewer throws than it takes your friends.

The fun part is throwing the disc far. Flying discs can travel much, much further than most other objects thrown by hand such as a baseball or football. The world record for throwing a golf disc stands at over 1,100 ft.

The hard part is throwing the disc accurately. Unlike a spherical object, the trajectory of a flying disc is not something easily graphed and calculated in your Physics 101 class. A ball thrown up in the air follows a relatively predictable parabolic path largely determined by the force of gravity acting on the sphere. It goes up, it comes down, easy-peasy.

The force of gravity also applies to a spinning disc as it flies. However, the unique shape of the disc, and the rotational torque (spin) acting on it, makes for a much more complex physics problem to solve. Disc golf is all about solving this physics problem in real time and in the real world.

As an object, such as a disc, flies through the air, it is constantly bumping into gas particles in the atmosphere which gradually slow the disc down until it eventually comes to a stop on the ground, this is wind (air) resistance. Also, the shape of a spinning disc thrown through the air generates lift, similar to the wings of an airplane. This means the air passing around the disc as it’s flying exerts an upward force which keeps the disc aloft longer, and this is why discs can be thrown so much further than a sphere. In summary, the air particles a disc encounters on its flight are responsible for both slowing down the disc due to air resistance, and for keeping the disc aloft due to lift. Fascinating!

Now here’s where it gets really complicated. You see, flying discs do not travel in a straight line. A disc thrown through the air will actually travel in an S-shaped line. If thrown by a right handed player, a disc will spin clockwise when viewed from above. When a disc leaves the golfer’s hand the clockwise spin will cause it to first start to drift to the right, then as the disc slows down it will start to drift back to the left, before finally landing on the ground. This property of flying discs to travel in an S-shaped line is termed stability.

Stability is a result of rotational torque and unequal air pressures generated on opposite sides of the disc. Think about the clockwise spinning disc described above. The left side of the disc (at the 9 o’clock position) is spinning into the wind, in the same vector as the trajectory of the disc. The right side of the disc (at the 3 o’clock position) is spinning away from the wind, in the opposite vector of the disc’s flight. This results in a high air pressure system on the left side of the disc, and a low air pressure system on the right side. Higher air pressure on the left means greater lift on the left. That unequal lift result is a gradual drifting of the disc to the right as it flies, and this is the first half of the S-shaped flight path caused by a disc’s stability.

To understand the second half of stability, we need to introduce another concept called gyroscopic precession. This is another complicated piece of physics, but it’s the same principle that keeps you from falling when riding on a hoverboard, and it’s what allows helicopters to maneuver around in the air. Gyroscopic precession says that if you apply a perpendicular force  to a spinning object, that force will be seen 90 degrees away in the direction of spin from where the force was applied. So if we have a clockwise spinning disc, and we apply an upward force at the 12 o’clock position, the disc will feel an upward force at the 3 o’clock position. Another example would be if we applied a downward force at the 7 o’clock position, then the disc would feel a downward force at the 10 o’clock position.

After the disc has traveled through the air for a bit it will start to slow down due to wind resistance. This means the disc will be moving at a slower velocity through the air, and will also be spinning at a slower rate. Slower speed through the air means less lift force acting on the disc and the disc will start to fall toward the ground. When the disc starts to fall, instead of the front of the disc slicing straight through the air like it did when it first left the golfer’s hand, the directional force of the air starts to push upward underneath the front of the disc. In other words, the disc is falling onto the air while it flies forward, and the air is now applying an upward force against the front of the disc.

So our disc is spinning clockwise, and now there is an upward force applied at the front of the disc (12 o’clock), then according to gyroscopic precession, the disc should feel an upward force at the 3 o’clock position (the right side of the disc). This upward force on the right side of the disc causes it to drift back toward the left until it eventually slows down to the point of landing on the ground.

Okay, that was a lot, let’s put it all together! A golf disc is thrown by a right handed player. The disc starts out flying through the air very fast and spinning at a high rate in a clockwise direction. The fast spinning disc creates higher pressure on the left side than the right due to air resistance. This left side pressure lifts and pushes the disc to the right as it’s flying. The disc starts to slow down and begins to fall, resulting in an upward force of air against the front of the disc. This upward air force produces a gyroscopic force 90 degrees away at the 3 o’clock position. The upward force on the right side of the disc causes it to fly back toward the left while the disc continues to slow and eventually lands on the ground.

Now that we know how discs are supposed to fly and how the atmospheric forces determine a disc’s flight, what changes should we expect to see when playing disc golf at high altitude?

At 9,000+ ft elevation there are significantly fewer gas particles in the atmosphere for discs to bump into during their flight. A disc will have less air resistance to deal with. That means it should fly faster and further, right? Not necessarily.

Remember, the atmosphere not only slows the disc down due to air resistance, it also provides the lift that keeps the disc up in the air for so long. Less gas particles in the atmosphere also mean less lift force.

So do discs fly shorter, further, or the same distance at high altitude? The answer is, it depends. Again, flying discs are a much more complicated physics problem than a flying baseball. Discs may fly further or shorter distances at high altitude compared to sea-level, but it depends on the type of disc, the player, and a whole host of other environmental factors such as specific elevation, temperature, humidity, and the direction of the wind.

What we can say, however, is that discs do fly differently at altitude. The shape of the S-path a disc takes at high altitude will look different due to the reduced air density, and this can spell trouble for a disc golfer who’s expecting their disc to turn right but instead it turns left.

During the first half of the stability S-curve, the disc is normally pushed toward the right due lift pressure created by air resistance. At high altitude less air resistance means less lift pressure generated during this first half of the S-curve, so the disc doesn’t move toward the right as much.

The second half of the S-curve is also changed. As we said before, less atmosphere mens less lift, so the disc will start to fall from its flight path sooner at high altitude. That means the upward air force on the front of the disc that results when it starts to fall will also occur sooner in the disc’s flight. Remember, this is the force that is felt by the disc 90 degrees away on the right side of the disc and pushes the disc to the left for the final part of its flight path.

At high altitudes discs drift less toward the right during the first half of their S-curve, and they begin the second half of their S-curve sooner along their flight path. The result is discs fly not so much in an S-shaped path, but rather a J-shaped, or hook-shaped path.

There you have it, High Altitude Disc Golf in a nut-shell. It was initially very frustrating when I started playing disc golf in Summit County. High altitude disc golf forces you to think about each hole and and each shot differently than you might at sea-level. The thin air changes the game dramatically, but that’s what I love most about disc golf. It’s a game that is virtually impossible to master, constantly challenges you, and can be enjoyed outside in the most beautiful and most extreme environments. Pick out a disc at your local sporting goods store and give it a try.