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A tippe top is a kind of top. When a tippe top is spun at a high angular velocity, its handle slowly tilts downwards more and more until it lifts the body of the top off the ground with the stem pointing downward. As the top's spinning rate slows, it loses stability and eventually topples over. At first glance the top's inversion may mistakenly seem to be a situation where the object gains energy. This is because the inversion of the top raises the object's center of mass, which means the potential energy has increased. What causes the inversion (and the increase in potential energy) is a torque due to surface friction, which also decreases the kinetic energy of the top, so the total energy does not actually increase. Once the top is spinning on its stem, it does not spin in the opposite direction to which its spin was initiated. For example, if the top was spun clockwise, as soon as it is on its stem, it will be still be spinning clockwise viewed from above. This constant spin direction is due to conservation of angular momentum. ==Theory== It is usually assumed that the speed of the tippe top at the point of contact with the plane is zero. However, as indicated by P. Contensou, 〔P. Contensou, Couplage entre frottement de glissement et frottement de pivotement dans la théorie de la toupie Symposium Celerina, Gyrodynamics, August 20–23, 1962 (2nd edn.), Springer (1963)〕 this assumption does not lead to a correct physical description of the top's motion. The unusual behavior of the top can be fully described by introducing dry friction forces at the contact point.〔V.Ph. Zhuravlev and D.M. Klimov, On the dynamics of the Thompson top (tippe top) on the plane with real dry friction, ''Mechanics of Solids'', 40(6):117-127, 2005.〕 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「Tippe top」の詳細全文を読む スポンサード リンク
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