Difference Between Wind And Air
Wind is air in motion. You cannot see the wind, but you can feel it and you can see its effects when it picks up and moves objects such as leaves or dust. Some winds have special names, such as monsoon or chinook. But winds are usually named after the direction they come from, and this also tells us about the effect of winds. For example, a north wind blows from the north. In the Northern Hemisphere, a north wind usually brings cold air from regions near the North Pole.
Winds are classified by speed. Winds between 32 and 63 miles (51 and 101 kilometers) per hour are called gale force winds. Winds of at least 74 miles (119 kilometers) per hour are called hurricane force winds. Wind speed is seldom steady, however. It can have fast periods called gusts and slow periods called lulls.
The Significance of Winds
Winds make Earth more livable by reducing the extreme heat of the tropics with cold air from the polar regions and by warming frigid polar regions with warm air from the tropics. Winds increase the evaporation of water from oceans, lakes, and even living plants, and they can transport this evaporated water thousands of miles. Winds can also help cool our bodies on hot days. In the winter, however, the combined effect of winds and cold temperatures can cause a potentially life-threatening effect called wind chill.
Winds also provide a source of nonpolluting energy and power. For example, large groups of windmills now produce electricity in some places in California. Winds also power groundwater pumps in some places, blow sailboats across lakes and oceans, and dry freshly washed clothes hung outside.
Air is a mixture of gases, mainly oxygen and nitrogen. Air exerts a pressure of about 1 kg on each cm (14 lb on each in2) of the Earth’s surface; this sea-level reading is called 1 atmosphere (1 atm) of pressure. Up to the height of the stratosphere, the second lowest atmospheric layer, the remaining chief constituents of dry air are argon (0.93%) and carbon dioxide (0.03%). Water vapor is present in variable amounts, mostly in the lower atmosphere. It can make up from near zero to 4% of the mass of air.
Air’s principal gases are nearly transparent to the Sun’s rays; despite this, water vapor and carbon dioxide absorb and emit long-wave radiation, resulting in the greenhouse effect. Stratospheric ozone absorbs a large amount of ultraviolet light from the Sun, heating the stratosphere and protecting life on Earth from the lethal radiation (see ozone layer).
Air pressure decreases rapidly with altitude. It is only 0.1 atm at an altitude of 16 km (10 mi) and 0.01 atm at 32 km (20 mi). Air density varies mostly with pressure over large vertical distances; at constant height, however, pressure variation with temperature becomes important. Air weighs roughly one kilogram per cubic meter (1 oz/ft3) at sea level. At an altitude of 3 km (2 mi), however, density is 30% less, causing initial breathing difficulties for many people from lowlands. The world’s highest permanent settlements are at altitudes of nearly 4 km (3 mi); mountaineers climbing the highest peaks (up to 8,800 m/5 mi) must carry oxygen.