Clock explained to kids

A clock is a device that tells time. Clocks can be mechanical, electrical, electronic, or atomic. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units: the day, the lunar month, and the year. Devices operating on several physical processes have been used over the millennia. A sundial shows the time by displaying the position of a shadow on a (usually) flat surface, which has markings that indicate the hours.[1] There are a number of ways to define the hour. The United Nations uses the term "mean solar time" of a particular place. Clocks can be used as timekeepers, alarms, or decoration. They can be wall-mounted, floor-standing, or placed on a desk or table. Some clocks have a pendulum, a weight that swings back and forth to keep the clock's hands moving. Clocks that use electrical power are called electric clocks. Clocks that use radioactive decay to measure time are called radioactive clocks. The first mechanical clocks were invented in the 14th century. They were powered by a falling weight, and they had to be reset every day. The first electrical clock was invented in 1876. It was powered by a battery, and it did not have to be reset. Clocks that use electronic circuits are called electronic clocks. They are the most accurate clocks. Atomic clocks are the most accurate clocks. They use the vibrations of atoms to measure time. Clocks are used to measure time. The first clocks were invented in the 14th century. They were powered by a falling weight, and they had to be reset every day. The first electrical clock was invented in 1876. It was powered by a battery, and it did not have to be reset. Clocks that use electronic circuits are called electronic clocks. They are the most accurate clocks. Atomic clocks are the most accurate clocks. They use the vibrations of atoms to measure time.