【单选题】__________________________________ Before pendulum clocks were invented, Peter Henlein of Germany invented a spring-powered clock around 1510. It was not very precise. The first clock with a minute ha...
【简答题】A pendulum clock depends on the period of a pendulum to keep correct time. Suppose a pendulum clock is keeping correct time and then you slide the bob of the pendulum downward on the oscillating rod. ...