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لا ملخص تعديل
[[ملف:PrecessionOfATop.svg|thumb|left|300px|The [[torque]] caused by the two opposing forces '''F'''<sub>g</sub> and -'''F'''<sub>g</sub> causes a change in the [[angular momentum]] '''L''' in the direction of that torque. This causes the top to precess.]]
ينتج حركة البدارية عن [[العزم الزاوي ]] للحركة الجسم والعزم الزاوي الناتج عن
Precession is the result of the [[angular velocity]] of rotation and the angular velocity produced by the torque. It is an angular velocity about a line which makes an angle with the permanent rotation axis, and this angle lies in a [[Angular momentum|plane]] at right angles to the plane of the couple producing the torque. The permanent axis must turn towards this line, since the body cannot continue to rotate about any line which is not a principal axis of maximum [[moment of inertia]]; that is, the permanent axis turns in a direction at right angles to that in which the torque might be expected to turn it. If the rotating body is [[Symmetry|symmetrical]] and its motion unconstrained, and if the torque on the spin axis is at right angles to that axis, the axis of precession will be perpendicular to both the spin axis and torque axis.