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 only just perceptible.

• 实际上，一根重约十吨、每分钟三千转的转子可以平衡得非常好，以至除了声音之外，勉勉强强地觉察它在运动。