There is an interesting phenomenon, I don't know if you have noticed: the clock hanging on the wall, when the battery is exhausted and stops running, its second hand always stops at the position of "9" on the dial. Why is that? When the battery in the quartz clock runs out and the second hand stops on the dial, gravity creates a large counter-torque. We know that the second hand moves clockwise, so gravity here produces a large counter-torque: counterclockwise. Gravimetric moment = magnitude of gravity × gravimetric arm. When the second hand arrives at 9 on the dial, the distance between the fulcrum and the direction of gravity action is large, that is, the gravity arm is large, so the moment of gravity is large, so the second hand will stop at 9 on the dial. The power is out, it will be a little bit above and below 9, and the tolerance range is very small. The second hand of a quartz clock moves downwards as it moves from the number 12 to the number 6. The force of gravity on the second hand will help it turn clockwise. When the second hand moves from the number 6 to the number 12, it is in upward motion, and the force of gravity will become resistance to the rotation of the second hand. When the second hand moves to the number 9, the resistance arm is long, making the resistance moment of gravity large.