Air around us

 Characteristic of air

Air iss a gas, air can be compressed, that is, the molecules can be moved closer together. If no force compresses the air, it will expand indefinitely to fill the space available. The volume occupied by a given amount of gas varies with the temperature and pressure of the gas.

Air as amoving object(WIND)

Wind is the movement of air caused by the uneven heating of the Earth by the sun. It does not have much substance—you cannot see it or hold it—but you can feel its force. It can dry your clothes in summer and chill you to the bone in winter. It is strong enough to carry sailing ships across the ocean and rip huge trees from the ground. It is the great equalizer of the atmosphere, transporting heat, moisture, pollutants, and dust great distances around the globe. Landforms, processes, and impacts of wind are called Aeolian landforms, such as sand dunes and Loess deposits, which are deposits of silt.

Air under pressure 

atmosphere as a large ocean of air surrounding the earth. The air that composes the atmosphere is made of many different gases. Nitrogen accounts for as much as 78% of the volume while Oxygen accounts for 21%. The remaining 1% is composed of such gases as Argon, Carbon Dioxide, Helium, and Hydrogen. Typically, the weather of the earth is caused by processes that occur within the lowest 20 km of the atmosphere. This includes such phenomena as fog, wind, rain, storms, snow, tornadoes, and 

Air and consequently, our atmosphere, do have weight. This weight decreases as you go up within the atmosphere. When gravity acts on the air, the air exerts a force upon the earth called pressure. The typical pressure at sea level is 1013.25 millibars or 14.7 pounds per square inch. A millibar is a unit that is used to report the the atmospheric pressure. Do you think that air pressure varies with respect to air temperature? Take a few moments to think about it.

Air is not just empty space—it has substance, or mass. Air has molecules that are constantly moving. Because air has mass, Earth’s gravity attracts it and gives it weight. Because it has weight, and the air molecules are constantly bumping into things, it exerts pressure.

Air acts as a medium for transmission of sound. When a sound wave passes through air, the particles of air vibrate back and forth, parallel to the direction of the sound wave. Thus, when a sound wave travels in the horizontal direction, then the particles of the medium also vibrate back and forth in the horizontal direction. Sound cannot travel without a medium and thus we cannot listen to sounds in the vacuum because of absence of air.