| Summary: | 碩士 === 逢甲大學 === 機械工程學所 === 99 === Using the paper with the mass of 0.12g to make a cone, the lateral surface of the cone cut out equally to form as the three, four, five and six triangular blades split-cone; the cone angle varied from 60° to 110°. Digital camera is used to record the whole process of the cones which fell down freely from 3m high. The falling height and angular velocity was converted into the speed, the acceleration and the angular acceleration for calculating the air resistance of axis and radius acts on the cone. Results show that free falling cones accelerate linearly to achieve terminal velocity, after then it descends to the ground with constant speed. The falling process of the split-cone was divided into three stages, the first stage is the accelerating process, the second stage is deceleration when angular velocity increases to exceed a critical value, the final stage is the constant speed process. In the falling process, the cone has the larger terminal speed with make it lands quickly. In the falling process of the spilt-cone, not only the axis air resistance acts on the cone surface, but also the shear force by air flow acts on the cone and make it spin. The radius air resistance that increases with angular velocity make the spilt-cone lands slowly, obviously decelerate the falling velocity and abate the terminal velocity. Results show that for the same cone angle of the split-cone, numbers of blade affect the axis air resistance less. The spilt-cone with less blades has faster angular velocity, indicates that the radius air resistance is larger and makes the split-cones land slowly. The bigger cone angle of split-cone with the same number of blade spins slowly and has lower radius air resistance, but it lands slowly and has lower terminal velocity because of the higher axis air resistance. So, the radius air resistance dominate the free fall process of split-cone with small cone angle and the axis air resistance dominate split-cone with large cone angle.
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