Category Science

How is steel made?

            Steel is made from iron, which is usually mined in the form of iron ore. The ore needs to be smelted in order to extract the iron. Smelting is done in a blast furnace, where coke and limestone are added to the iron ore. This mixture is heated to a very high temperature and air is blown through it. The molten iron is drawn off.

            To make steel, iron is mixed with carbon and other metals to give it extra harness. There is about 1.6 percent carbon in most steel. Other forms of steel contain elements such as chromium and nickel to prevent rusting. Ordinary carbon steel rusts as easily as iron, and must be protected with paint or other coatings.

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How do jet engines work?

            Like rockets, jet engines propel an aeroplane with a stream of hot gases. Unlike rockets, which produce hot gas as a result of burning an explosive mixture, jet engines burn fuel in the air that they draw in at the front of the engine?

            Air enters the front of the engine and is compressor wheel. Fuel is injected into the compressed air, burns fiercely and expands. The hot gas rushes out of the jet pipe at the rear of the engine. The hot gas passes through a turbine, which drives the compressor at the front of the engine.

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How does an aeroplane fly?

               As an aeroplane moves though the air, the air passes over the surface of the wings. These are shaped with a curved top surface and a flatter lower surface, which means that air passing over the top of the wing, has to travel a little faster than that below the wing. This lowers the pressure above the wing, while the air pressure below pushes up, and the end result is the lift that keeps the aeroplane in the air.

               The tail surfaces keep the wing at the proper angle to provide the right amount of lift. The power to propel the aeroplane can come from the engines or, in the case of gliders, from rising air currents.

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How were calendars developed?

 

 

               Calendars have been used for thousands of years. The early ones were usually based on the phases of the Moon and the movement of the Sun. We still depend largely on the natural movements of the Earth, Moon and Sun to divide up time. The calendar we use today is based on the Julian calendar, which, was introduced by the Romans in 46 BC. It had 365 days, and the Romans had not yet discovered the need for leap years. By 1582 the Julian calendar was ten days out, and Pope Gregory decreed that ten days would have to go missing from that year. This caused rioting because people felt that ten days of their lives had been stolen.

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What is Greenwich Mean Time?

               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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How do we measure time accurately?

               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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