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The mathematics of pendulums are in general quite complicated. Simplifying assumptions can be made, which in the case of a simple pendulum allows the equations of motion to be solved analytically for small-angle oscillations. == Simple gravity pendulum == A so-called "simple pendulum" is an idealization of a "real pendulum" but in an isolated system using the following assumptions: * The rod or cord on which the bob swings is massless, inextensible and always remains taut; * The bob is a point mass; * Motion occurs only in two dimensions, i.e. the bob does not trace an ellipse but an arc. * The motion does not lose energy to friction or air resistance. * The gravitational field is uniform. * The support does not move. The differential equation which represents the motion of a simple pendulum is where is acceleration due to gravity, is the length of the pendulum, and is the angular displacement. , where is the length vector of the pendulum and is the force due to gravity. For now just consider the magnitude of the torque on the pendulum. : where is the mass of the pendulum, is the acceleration due to gravity, is the length of the pendulum and is the angle between the length vector and the force due to gravity. Next rewrite the angular momentum. :. Again just consider the magnitude of the angular momentum. :. and its time derivative :, According to , we can get by comparing the magnitudes :, thus: : which is the same result as obtained through force analysis. }} |} = \sqrt \\ & = 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Pendulum (mathematics)」の詳細全文を読む スポンサード リンク
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