Physics of a Frisbee – the ultimate way of throwing a frisbee
Summer is coming! This means chilling in the park or at the beach. And what would a nice day of recreational activities be without throwing a frisbee? I’ll tell you.
So, you go out, hyped up to throw a frisbee and then this happens to you:
You don’t want that to happen to you, right? Well, as a wise woman once said: Theory first, then practice!
To learn how to throw a frisbee well it is very helpful to understand the physics of its flight. To get to the bottom of this matter let’s make an unconventional turn ask first:
Why shouldn’t a frisbee fly?
First of all, of course gravity. Apart from very few lucky people none of us have ever experienced weightlessness so gravity is something we don’t usually think about, we don’t even really feel it. I mean when was the last time you were sitting and thought: “Ah yes, the pressure on my butt; it’s because of gravity” (Now I just made you conscious about the pressure, right?)
Gravity is the force that pulls everything towards the middle of the earth. Practically, given that we are standing on the earth this means that everything gets pulled down towards the ground. So, how do we make the frisbee fly? We must apply a force to the disc that will counteract the force of gravity. Meaning we have to throw the frisbee; the harder the further it goes.
As you can see it’s not just gravity that affects the flight of the frisbee. Even though these guys are throwing with a lot of force it does not really fly that far. That is because of all the air around us. Another thing we tend to forget about, even though we are breathing air in and out all the time. Air having mass was a hot debated topic until proven in 1644. Friction with air slows down any object. This is called air resistance or drag and its dependent on the surface of attack the air is presented with. The more surface of attack presented the more it slows the object down. Therefore, the key to reduce the friction is to present the air with as little surface to attack as possible.
And there is another important reason to throw a Frisbee on one plane. As you can see the frisbee’s edge is slightly curved, just like an airplane wing. That helps a frisbee to generate lift. Lift is a force perpendicular to the direction of the airflow and in the case of the Frisbee lift pushes the Frisbee upwards. But Lift does not only depend on the shape of the Frisbee. More important is the angle of attack that the Frisbee is released at.
If the angle of attack is positive the air is directed down (see picture) and according to Newton’s Third Law (every force has a counter force) the disc is pushed up. With a negative angle of attack the air is pushed up and the frisbee down. A too steep angle however will just slow the flying disc a lot, because of the increased friction with air. The optimal angle to throw at is about 10-20°.
So as you may have noticed it is very important to keep the frisbee on a single plane. And you probably know how: by giving it a good spin.
Normally a disc would be very unstable. It wobbles and turns.
By spinning it, it stays on one plane. Any spinning object will have the tendency to stay stable on its spinning plane due to angular momentum. This is how spinning tops don’t fall over.
And as you may have learned as a kid. The more spin you give it the longer it will not fall over. The same applies for a flying disc. The more it spins the more stable its flight is and the farther it goes.
So, if you want to throw the frisbee really well give it a good spin with your wrist, throw it hard, in one plane and with a slight positive angle of attack.
Here you can see Brodie Smith one of the best throwers out there:
Unfortunately, theory isn’t enough or as Yogi Berra once said:
“In theory, there is no difference between theory and practice. But in practice, there is.”
So, go get some practice and impress your friends with your new sciency frisbee skills
What do you think the Worldrecord in distance for throwing a Frisbee is? 50 meter? 70 meters?
It’s 338 meters. Crazy right? That’s like 3 footballfields.
During my research I found out that the most common theory in textbooks and on the internet about how lift is generated is wrong.
NASA explains why: https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html
Here are some good pages that explain how lift works in regards to a frisbee: