Big Ben Originally the nickname of the
bell in the clock tower of the Houses of Parliament, London, and now by
association the clock and its tower. The bell, 19 ft in
diameter and weighing 13 tonnes, was cast in 1858.
A catalytic converter is used to reduce the amount of harmful gases pumped into the atmosphere by vehicles. The converter is a metal case containing a metal or ceramic in the shape of a honey comb which is coated with a precious metal like platinum or rhodium which acts as a catalyst. The converter is fixed into the exhaust pipe of the vehicle. As the engine's exhaust gases flow through the honey comb, the catalyst converts the harmful gases like carbon monoxide, oxides of nitrogen and hydrogen into water vapour and carbon dioxide.
T he first known Olympic games were held at Olympia in Greece in 776 B.C . They grew out of a religious ceremony held there that involved a sprinting race, They were held after every four years after a legend that the race of the religious ceremony should be done after four years. The Greek games ended in 394 A.D . 1500 years later, the modern Olympics were revived in 1896 and it was decided to stage them after every four years, exactly as it was done during ancient Greek times. Olympics have become the most magnificent sports festival of the world. Each time they are held in a different country where athletes from different nations compete in races , jumping, gymnastics, football, yatching and many more contests.
Artificial satellites sent from the Earth orbit around the earth. The ones near the Earth orbit faster than the ones far away. A satellite 35,900 Km above the Earth's surface, takes 24 hours to orbit once. The satellite is always above the same point on the Earth's surface as the planet rotates. Geostationary orbit is also called as geosynchronous ' orbit. Such satellites are used to receive telephone and television signals and retransmit them over long distances.
O ur nose and mouth have special receptor cells, which when stimulated by chemical molecules, send nerve impulses to the brain. Our tongue is covered with tiny growths or papillae. Some papillae contain small group of cells known as taste buds. Each taste bud contains four to twenty receptor cells with short sensory hair. These hair react to molecules dissolved in the saliva. We can taste four main kinds of tastes. Bitterness is tasted at the back of the tongue, sourness at the sides , sweetness at the front and saltiness can be tasted all over. Our nose has cell receptors at the roof of the nasal cavity. These receptors have sensory hair that branch and project into the mucus that lines the cavity. Molecules in the air dissolve in the mucus and stimulate these hair. There are about 15 kinds of smell receptors which can detect over 10,000 different smells .
A ir-traffic controllers make sure that planes take off and land safely and fly without any delays. The pilots are told where to fly so that no air collision takes place. The radar provides the air-traffic control staff with updated information about the exact position, destination and identity of every plane and about the weather conditions. When a plane is about 2,700 metres away from an airport and 600 metres above it, it enters the terminal control area. Working from this centre, the controller guides the pilot telling him at which height to fly or wait and circle the airport, when the plane has to land, etc. The controllers are also responsible for aircraft taking off and they also control planes throughout their flight from one airport to the next.
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