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Frisbee | |
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Introduction
If you have ever been to the park or the beach, you've probably have seen one of these plastic discs flying through the air. We're not talking about a UFO, we're talking about the Frisbee, more commonly known as the flying disc. The Frisbee has been around for a long time and has become as common to us as the baseball or the football. The Frisbee has even developed sports of its own. Some Frisbee games, like Frisbee Golf (Folf) and Frisbee Baseball imitate (copy) existing sports. Other games, such as Ultimate Frisbee and Guts were inspired by the Frisbee itself. Frisbee catching has even become a popular sport for dogs! Why are we so fascinated (interested) with this plastic flying disc? Perhaps we are amazed by the fact that such a simple object can glide effortlessly through the air. Maybe we are soothed by its graceful flight patterns, or maybe Frisbees are just fun to throw. Let's take a closer look at the flying toy that has become so popular in today's society. History
Frisbees, over the years, have remained the same size and shape. The original Frisbees were actually pie tins, back in the late 1800's. College students, in those days, would toss the pie tins back and forth to each other. Then, it was common for the pie companies to have their name on each of their pie tins. One pie company, the Frisbie Pie Company, owned by William Frisbie, produced a pie tin which was popular with Yale students. The Yale students started calling these flying pie tins by the name that was on them. Since then, the name Frisbie (now Frisbee) became the popular term for one of today's most well known flying toy. Dynamics What makes a Frisbee fly? Just like a bird's wing or the wing of an airplane, shape plays a large part in influencing the flying ability of the Frisbee. The design of the Frisbee has not changed much from its beginnings as a pie tin. It is still light weight, circular, fairly flat, and the edges of the Frisbee are either sloped or rounded. If we take a look at the Frisbee from the side we can see that the rounded edges of the Frisbee look similar to the front edge of an aircraft wing. We know that the curved upper surface of the wing is what generates (causes) lift. The same principle applies to the Frisbee. As air passes over the curved upper surface of the Frisbee it speeds-up, creating a low pressure region on top of the Frisbee. Below the Frisbee air passes more slowly, creating a high pressure region. The difference in pressure gives the Frisbee lift.
The shape of the Frisbee generates lift, but it needs more than that for flight. Try throwing a Frisbee without spinning it. Notice how it wobbles and tumbles. The shape of the Frisbee may be generating lift, but the Frisbee is unstable. It cannot stay upright and eventually stalls (falls). All flying things must have something which makes them stable during flight; airplanes and birds have tails, rockets have fins. For a Frisbee it is the spinning motion generated from the Frisbee throw, which stabilizes the Frisbee as it flies. Why does spinning make a Frisbee stable in flight? All things which spin are said to possess "angular momentum". Angular momentum has two aspects: magnitude and direction. Magnitude may be thought of as the force generated by the spin; and is related to the rate of spin and the mass of the object. This force overcomes drag, and airflow, until the spin rate decreases, stops or meets a stronger force, such as a strong wind (torque), or hitting the ground. Direction is determined (decided) by whether the disk is turning clockwise or counter-clockwise.
Take the gyroscope for example. Start a gyroscope spinning. Then grab the ends of the gyroscope with your hands. Now try to turn it upside-down. You'll notice it takes effort to do this. This is angular momentum in action. This is what keeps a Frisbee steady in the air. The stabilizing effects of spinning can be seen in other things as well. Take for example, the top. A non-spinning top will always fall on its side. Only when the top spins is it able to dance on its tip. A bicycle also benefits from angular momentum. When at a stop sign it is difficult for a bicyclist to balance on the two wheels of a bicycle. When the bicyclist starts moving the pedals on the bicycle, making the wheels spin, the angular momentum of the wheels makes it much easier for him/her to balance.
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