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This article describes a particle in planar motion〔See for example, , 〕 when observed from non-inertial reference frames.〔''Fictitious forces'' (also known as a ''pseudo forces'', ''inertial forces'' or ''d'Alembert forces''), exist for observers in a non-inertial reference frames. See, for example, , (NASA: ''Accelerated Frames of Reference: Inertial Forces'' ), (Science Joy Wagon: ''Centrifugal force - the ''false'' force'' )〕 The most famous examples of planar motion are related to the motion of two spheres that are gravitationally attracted to one another, and the generalization of this problem to planetary motion. See centrifugal force, two-body problem, orbit and Kepler's laws of planetary motion. Those problems fall in the general field of analytical dynamics, the determination of orbits from given laws of force.〔 〕 This article is focused more on the kinematical issues surrounding planar motion, that is, determination of the forces necessary to result in a certain trajectory ''given'' the particle trajectory. General results presented in fictitious forces here are applied to observations of a moving particle as seen from several specific non-inertial frames, for example, a ''local'' frame (one tied to the moving particle so it appears stationary), and a ''co-rotating'' frame (one with an arbitrarily located but fixed axis and a rate of rotation that makes the particle appear to have only radial motion and zero azimuthal motion). The Lagrangian approach to fictitious forces is introduced. Unlike real forces such as electromagnetic forces, fictitious forces do not originate from physical interactions between objects. ==Analysis using fictitious forces== The appearance of fictitious forces normally is associated with use of a non-inertial frame of reference, and their absence with use of an inertial frame of reference. The connection between inertial frames and fictitious forces (also called ''inertial forces'' or ''pseudo-forces''), is expressed, for example, by Arnol'd: A slightly different tack on the subject is provided by Iro: Fictitious forces do not appear in the equations of motion in an inertial frame of reference: in an inertial frame, the motion of an object is explained by the real impressed forces. In a non-inertial frame such as a rotating frame, however, Newton's first and second laws still can be used to make accurate physical predictions provided fictitious forces are included along with the real forces. For solving problems of mechanics in non-inertial reference frames, the advice given in textbooks is to treat the fictitious forces like real forces and to pretend you are in an inertial frame. It should be mentioned that "treating the fictitious forces like real forces" means, in particular, that fictitious forces as seen in a particular non-inertial frame transform as ''vectors'' under coordinate transformations made within that frame, that is, like real forces. 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「Mechanics of planar particle motion」の詳細全文を読む スポンサード リンク
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