In practice ,a rotor weighing about 10 tons and rotating at 3,000 r .p .m. may be so well balanced that the motion ,except for sound ,is just perceptible.

• 实际上，一根据重约10吨、每分钟3000转的转子可以平衡得非常好，以致除了响声外，人们几乎觉察不出它是在转动。