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Professional Frisbee]] SUITABILITY OF A DISC A disc is suitable for flight if its Air Resistance s in different directions are of an appropriate relationship, allowing its flight path to be more efficient in the direction in which it is thrown; and it can therefore be thrown far further than a ball. The disc must also be made of an adequately dense material so that its air resistance is low yet the force exerted by gravity is low enough for air flight. The shape of the disc must be suited to the throwing action, so a flat disc would be inappropriate due to the lack of grip that the thrower could get from the disc, resulting in accidental release. AIR RESISTANCE The two major types of flying disc are the conventional design used in both Ultimate and Disc Golf and the aerobie ring. Although these designs are very different, they both use air resistance in the same way to fly. Effect on flight distance When a spherical ball flies through the air it has the same cross-sectional profile causing air resistance in all directions, but the flying disc does not. Its shape causes it to have much more vertical air resistance (assuming horizontal flight) than horizontal air resistance. This is partly due to the large circular cross-sectional area vertically, but is enhanced by the rim around the edge of the disc which encloses air inside the disc in the same way as a parachute. Because of this effect the disc is able to fly a longer horizontal distance in a flatter parabola. Effect on shape of path The angle at which the disc is thrown alters the ratios of air resistances in different directions, affecting the direction of flight. The aerobie The Aerobie is an alternative design of flying disc that, although differently shaped, still has very similar properties to the conventional disc. It has less air resistance both horizontally and vertically, but these forces are of a similar ratio to each other. Because there is less overall resistance to motion, the aerobie can fly farther than the conventional disc and holds the world record for the longest flight by a human-thrown projectile. However, due to the lack of a rim, the aerobie is less suited to angled, curved flights and air-bouncing. SPIN OF THE DISC The spin of the disc helps to keep the disc stable in flight and prevent unplanned tilting. This is because a large angular momentum stabilises the disc in the same way that it keeps a gyroscope steady, with the angular force forcing the mass of the disc away from the centre of mass, perpendicular to the axis of rotation. Any unequal force acting on a particular area of the disc is quickly redirected to be equal over the circumference of the disc. As the disc spins faster, it becomes more stable due to the rapidity of the equalisation of forces. THE CENTRE OF MASS On neither the aerobie or the conventional design is the centre of mass located on the disc itself, but rather in the space in the centre. MASS OF THE DISC The force required to accelerate the disc is directly proportional to the mass of the disc. This decreases the acceleration of the disc, assuming that the force of projection is constant. Therefore, discs come in a variety of weights, although those used for Ultimate are mainly 175 g in mass, heavier than the majority of discs and considerably heavier than an aerobie. SEE ALSO |
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