We all experience unbalance and balancing in everyday life: (1) washing machine on "spin dry" vibrating due to unevenly distributed clothes; (2) ceiling fan swaying back and forth as it spins; (3) getting new tires and you are asked if you would like your wheels "balanced". Picture or imagine: (1) spinning a Frisbee with a 1" sphere of clay stuck to one side; (2) swinging a stone around, overhead, on a string. In all the above examples: (1) the mass center and geometric center are misaligned; (2) there is an out of balance condition; (3) the object is not balanced or has unbalance. When an unbalanced object is spun, it vibrates in rhythm with the rotation and the forces caused by unbalance are relative to the square of the rotational speed. Two key equations are: Unbalance = Mass (or Weight) × Radius Displacement = Unbalance/Total Mass (or Weight) In the pages that follow, through stories, equations and problem solving, balancing is discussed as more math and common sense and less smoke and mirrors.
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