Chemical Change A change that produces one or more new substances and may release energy. Chemical Property A second set of properties in all kinds of matter. Circuit A path that is made from an electrical current. Claws A sharp, usually slender, and curved nail on the toe of an animal.
The hourglass was one of the earlier timekeeping devices and has become a symbol of the concept of time. For thousands of years, devices have been used to measure and keep track of time. The current sexagesimal system of time measurement dates to approximately 2000 BC from the Sumerians. The Ancient Egyptians divided the day into two 12-hour periods, and used large obelisks to track the movement of the sun.
the clock is one of the oldest human inventions meeting the need to consistently measure intervals of time shorter than the natural units the day the lunar month and the year