What tornadoes, hurricanes, typhoons and cyclones are

A twisting storm funnel, about 100 metres wide with winds inside it that could reach speeds of 350km/h is known as a tornado.

A torando moves in a straight line across land. Tornadoes are common on the Great Plains of North America. Did you know that at the centre or 'eye' of a tornado is an area of pressure so low that it can cause buildings to explode?

Storms that form over the Pacific Ocean are called typhoons and ones that occur over the Indian Ocean are called cyclones. Recently we were on alert over such a cyclone named Laila which was due to hit our shores. However, we escaped its wrath but India became a victim.

Hurricanes are devastating. They are also storms but are more powerful than the storms we experience in our part of the world. Hurricanes form over tropical waters in the Atlantic.

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What acid rain is

Rain, the very mention of the word may make some people nervous because the recent rainfall caused havoc in our country, flooding many areas. Acid rain is not like the normal rainfall we experience. It is harmful. Acid rain is formed when burning fossil fuels release sulphur dioxide and nitrogen dioxide into the air. When these two mix with water, a weak acid is formed and this eventually falls as 'acid rain.'

Acid rain does not fall always near the place the pollution occurs. It can fall far from the point of pollution. Acid rain kills many trees and acidifies rivers and lakes, harming wildlife. We can help reduce the problem of acid rain by reducing our use of fossil fuels.

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What binocular vision is

The field of vision directly ahead of you is known as binocular vision. The better it is, the easier it is to judge the size and distance of objects.

Owls have superb binocular vision among birds because they have eyes at the front of the head. Most birds have eyes on the sides. They have good all round vision to spot enemies, but very poor binocular vision. A Tawny owl may have binocular vision up to 60-70 percent but a Robin will have only about 10-30 per cent.

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What Yin and Yang are

It was a strong belief of the Chinese people that everything in nature was in harmony. Confucious, the great chinese philosopher depicted this by the Yin and Yang symbol. The dark Yin interlocks with the light Yang and each one contains a tiny bit of the other.

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Who designed the famous sail-like roof

Architect Jorn Utzon from Denmark designed the roof of the Opera House in Sydney Harbour to resemble wind-filled sails. The main roof was made from concrete segments covered with thousands of ceremic tiles. It took 15 years to build it. The Sydney Opera House was completed in 1973.

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