Pariksha SaathiLesson 5 of 8 · Science and its Pedagogy (Paper II)
Natural Phenomena and Natural Resources: Winds, Lightning, Earthquakes, the Solar System, Water, Forests and Pollution
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Rain, wind and cyclones
In the water cycle, water evaporates from seas, lakes and plants, condenses into clouds and returns as rain, hail or snow. Warm air expands and rises; wind blows from high pressure to low pressure, and high-speed wind is accompanied by reduced air pressure. Uneven heating of the equator and the poles, and of land and sea, drives winds such as the monsoon. A cyclone has a calm, very low-pressure centre called the eye; it is called a hurricane in the American continent and a typhoon in the Philippines and Japan, while a tornado is a dark, funnel-shaped cloud.
Thunder and lightning
Rubbing charges objects such as a plastic refill rubbed with polythene; like charges repel, unlike charges attract, and an electroscope detects charge. In a thunderstorm, air currents move upward and water droplets downward, separating charges: positive charges collect near the upper edges of the clouds and negative charges near the lower edges. When the charges grow very large, the air can no longer resist their flow, and lightning results; Benjamin Franklin showed lightning to be an electric spark. A lightning conductor carries the charge safely into the ground. No open place is safe: houses and closed cars or buses are, and outdoors one squats low with head between the hands, never lying flat, away from tall trees and running water.
Earthquakes
An earthquake is a sudden, brief shaking of the Earth caused by movement of the plates of its outer layer; plate boundaries are weak zones. In India, Kashmir, the Himalayas, the North-East, the Rann of Kutch, Rajasthan and the Indo-Gangetic plain are most prone. Strength is given on the Richter scale from seismograph records; destructive quakes exceed 7, and a quake of magnitude 6 has about 1000 times more destructive energy than one of magnitude 4. Bhuj in Gujarat was hit on 26 January 2001, and the quake of 8 October 2005, centred across the Line of Control, badly hit Uri and Tangdhar in north Kashmir. Quakes cannot be predicted, so buildings must be quake-safe, and during a quake one shelters under a sturdy table.
The Moon, stars and constellations
The Moon has no light of its own and reflects sunlight; its phases run from new moon to full moon in about 15 days, and we always see the same side. Star distances are given in light years, the distance light covers in one year; after the Sun the nearest stars are those of the Alpha Centauri system, about 4.3 light years away, of which Proxima Centauri is the closest. Stars appear to move from east to west because the Earth rotates from west to east, but the Pole Star seems fixed because it lies almost along the Earth's axis. Ursa Major (Saptarishi or the Big Dipper), Orion and Cassiopeia (a distorted W or M) are well-known constellations.
The solar system
The Sun and the bodies revolving around it, including eight planets, form the solar system; Pluto was reclassified as a dwarf planet in 2006. Mercury is nearest the Sun; Venus, the brightest planet, is called the morning or evening star though it is not a star, and rotates from east to west, as Uranus does; Mars is the red planet; Jupiter is the largest; Saturn has beautiful rings and is less dense than water. Asteroids orbit between Mars and Jupiter, Halley's comet returns about every 76 years, and meteors are shooting stars. Aryabhata, launched in 1975, was India's first artificial satellite.
Water and forests
About 71% of the Earth's surface is water, mostly salty; World Water Day falls on 22 March. Rain water seeping into the ground (infiltration) recharges groundwater, whose upper level is the water table. Overuse and deforestation lower the water table, so rainwater harvesting, traditional bawris and drip irrigation are needed. In a forest, decomposers turn dead matter into humus, so nothing is wasted. Forests release oxygen, absorb carbon dioxide, hold soil, soak up rain water and support food chains such as grass, deer, lion; deforestation brings soil erosion, floods, droughts and desertification.
Pollution
Air pollutants include carbon monoxide from incomplete burning, sulphur dioxide and nitrogen dioxide from burning fuels, and CFCs from refrigerators and aerosol sprays, which damage the ozone layer. Sulphur dioxide and nitrogen dioxide dissolve in rain to form acid rain, which corrodes the marble of the Taj Mahal (marble cancer), and carbon dioxide traps heat (the greenhouse effect), causing global warming. Water is polluted by sewage, industrial waste and farm chemicals; excess fertiliser makes algae grow, and their decay after death uses up the oxygen fish need. The Ganga Action Plan was launched in 1985. Boiling, filtration and chlorination make water safe; contaminated water spreads cholera, typhoid and jaundice.
Conservation
Wildlife sanctuaries, national parks and biosphere reserves protect biodiversity; the Pachmarhi Biosphere Reserve in Madhya Pradesh contains the Satpura National Park and the Bori and Pachmarhi wildlife sanctuaries. Endemic species live only in one area; NCERT names the sal, wild mango, bison and Indian giant squirrel as endemic there. The Red Data Book records endangered species. Project Tiger was launched in 1973, the Chipko movement began the same year, and recycling paper saves trees, since about 17 full-grown trees are cut to make one tonne of paper.
Key facts
- Wind blows from high to low pressure; high-speed wind means lower air pressure; the eye of a cyclone is calm; hurricane (American continent), typhoon (Philippines, Japan).
- Lightning: positive charges near the upper edges of clouds, negative near the lower edges; a lightning conductor carries charge safely into the ground; Benjamin Franklin linked lightning with electric sparks.
- Lightning safety: squat low with the head between the hands, never lie flat; avoid tall trees, open fields and running water; closed cars and buildings are safe.
- Earthquakes: Richter scale, seismograph; magnitude 6 has about 1000 times the destructive energy of magnitude 4; Bhuj 26 January 2001; the 8 October 2005 quake, centred across the Line of Control, badly hit Uri and Tangdhar in north Kashmir.
- A light year is a distance, not a time; the Pole Star seems fixed because it lies almost along the Earth's axis; Ursa Major = Saptarishi; Cassiopeia looks like a distorted W or M.
- Planets: Mercury nearest the Sun; Venus brightest and rotates east to west; Mars red; Jupiter largest; Saturn less dense than water; Pluto a dwarf planet since 2006; Aryabhata (1975) was India's first satellite.
- Water: about 71% of the Earth's surface; World Water Day 22 March; water table, aquifers, infiltration; rainwater harvesting and drip irrigation save water.
- Acid rain from sulphur dioxide and nitrogen dioxide causes marble cancer of the Taj Mahal; CFCs damage the ozone layer; carbon dioxide causes the greenhouse effect; Ganga Action Plan 1985.
- Pachmarhi Biosphere Reserve (Madhya Pradesh): Satpura National Park and the Bori and Pachmarhi sanctuaries; endemic as NCERT lists them: sal, wild mango, bison, Indian giant squirrel; Project Tiger 1973; Red Data Book lists endangered species.
Quick revision
Wind blows from high to low pressure; cyclone eye is calm; lightning from charge separation in clouds, conductor protects, squat but never lie flat; earthquakes from plate movement, Richter scale, Bhuj 2001; light year is a distance; Pole Star seems fixed; eight planets, Venus brightest, Jupiter largest; Aryabhata 1975; 71% of the surface is water, World Water Day 22 March; acid rain causes marble cancer; Ganga Action Plan 1985; Project Tiger 1973; Pachmarhi Biosphere Reserve.