自行车为什么骑起来才不倒？

A bike stands up when it moves. 自行车一动起来，自己就能站稳。 But at a stop, it falls right down. 可一停住，立马就往旁边倒。 Scientists give two big reasons. 科学家给了两个大原因。 First, a spinning wheel likes to stay straight. 第一，转起来的轮子，喜欢直着走。 They say this is the gyro effect. 这就是所谓的陀螺效应。 Second, the front wheel fixes itself. 第二，车把会自动回正方向。 Together they keep you safe and balanced. 两招合起来，你就稳稳当当不倒。