Category Science & Technology

               In 1884 an international conference decided that the 0 degree line of longitude, or meridian, would run through the Royal Observatory in Greenwich, England. As you move to the east from the Greenwich Meridian, the time is one hour ahead of Greenwich Mean Time for each degree you move. If you move to the west, time is one hour behind for each degree. Midday is the point where the Sun is highest in the sky, whichever time zone you are in.

               The amount of daylight varies with the seasons, so daylight – saving time or summer time, was introduced to make maximum use of daylight hours. In the northern hemisphere, clocks are reset one hour ahead in spring and one hour back in autumn. (In the southern hemisphere the seasons are reversed.

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               After the invention of sundials, other means of telling the time indoors were developed, such as hourglasses and burning candles. The invention of clocks, however, allowed far more accurate timekeeping. Early clocks were powered by a weight hanging from a fine chain (a pendulum), but later on springs were used to store energy. Most mechanical clocks and watches now contain a balance wheel that spins backwards and forwards, allowing an escapement wheel to move a very small amount each time it spins. This wheel is driven by the energy stored in the clock spring.

               Many watches and clocks are now powered by an electronic timer with no moving parts. It contains a tiny integrated circuit and a vibrating quartz crystal, which measures time with great accuracy.

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               The Earth spins on its own axis once every 24 hours, or day. The Earth orbits the Sun every 365  days, or year. Every 4 years we need to have a leap year with an extra day to make up the difference between the calendar year (365 days) and the time it takes for one complete orbit of the Sun. The year is divided into 12 months, which roughly correspond with the time it takes for the Moon to complete one full orbit of the Earth.

Picture credit: google

               Sundials are the simplest way to measure time during the day. A simple stick casts a shadow that grows shorter until midday, when the Sun is at its highest in the sky. The shadow grows longer again after midday. A sundial simply casts its shadow onto a plate marked with the hours. Sundials have been used for many centuries, and are still in use today.

               People have always organized their lives by the passing of time. The earliest hunters had to hunt during the hours of daylight. When farming had developed, it was important for farmers to understand the seasons in order to plant their crops at the right time.

               Long ago, people realized that the movement of the Sun allowed them to recognize the time of day. They also realized that the movement of the Moon was regular and could be used to give measurements of roughly one month. Modern life is governed much more by time, and we now depend on highly accurate clocks to measure every second of the day.

               For thousands of years people have used levers as a way of transferring a force from one place to another, and to change the amount of movement that results.

               To move a heavy object, a long lever can help. The lever is free to move about a point called the fulcrum. The shorter end of the lever is placed under the object, and force is applied to the longer end. This will cause the object to be lifted, but the long end of the lever will have to be pushed down a long way to lift the object only a short distance. With a long-enough lever you could lift a car for a short distance.