Rotating Stool

旋转椅

The moment of inertia is large with the masses held out. For a given angular momentum, the angular velocity is relatively low.

转动惯量与质量分布越远越大。对于给定的角动量，角速度相对较低。

If the masses are pulled in, the moment of inertia is considerably decreased. Conservation of angular momentum dictates that the angular velocity must increase.

如果质量被拉向中心，转动惯量会显著减小。角动量守恒定律规定，角速度必须增加。

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课堂演示

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视频示例

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Vector rotation examples

索引矢量旋转示例

HyperPhysics***** Mechanics ***** Rotation

HyperPhysics ***** 力学 ***** 转动

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Rotating Stool

旋转椅

Begin with the wheel rotating so that its angular momentum is upward. The man and the stool are at rest. The stool is on a bearing mount so that it can freely rotate.

从一个角动量方向向上的轮子开始。人和椅子静止不动。椅子装在轴承上，可以自由旋转。

If the wheel is turned over, its angular momentum is now downward. But since there is nothing to exert a significant torque on the system, the angular momentum must have the original value upward. The man and the stool begin to rotate with angular momentum twice that of the wheel.

如果轮子被翻转，其角动量现在是向下的。但由于系统中没有物体能对它施加显著的力矩，角动量必须保持原来的值，即向上。人和 stool 开始以轮子两倍的角动量旋转。