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。
