Our Earth has a blanker of air around it. The Earth’s gravity pulls the air column down hence, the air has weight. The weight of the air column (force) per unit area on the earth is pressure which is termed as atmospheric pressure.
Atmospheric pressure = weight of the air / area
The instrument used to measure the atmospheric pressure is called Barometer. The standard atmosphere is abbreviated as atm. One Atmosphere (1 atm.) is equal to 11,300 Pa or 101.3 kPa at sea level.
Do you knwo?
The atmospheric pressure around us at ground level is about 100,000 Pa (A00 kPa).
Material required:
Glass, think paper, water
Procedure:
- Take a glass and fill it with water up to brim.
- Put the paper on the glass.
- Hold and simply press the paper on the glass by keeping hand over the paper.
- Keep on hand over the paper, hold the glass from its lower part by your other hand and invert it.
- Remove the hand from the paper.
Does water fall down? If not what prevents it from falling?
Atmospheric pressure varies with altitude
The Earth’s surface where we live is the bottom of the sea of air. There is more weight of the air and hence more atmospheric pressure at the Earth\s surface. As we go up in the air, atmospheric pressure decreases. This is because weight of air decreases as we go up in the air. Thus the people who climb up the hills experience less air pressure than those living at sea level. At sea level the atmospheric pressure is 101300Pa (101.3kPa) whereas, at a height of about 5km it falls to about 55000 Pa (55kPa).
Altitude above the sea level can be determined on the basis of the measurement of atmospheric pressure. The lower the atmospheric-pressure the greater is the altitude. When a barometer is calibarted to indicate altitude, the instrument is called ‘Pressure Altimeter’. pressure altimeter is used in air crafts. Wrist-mounted altimeter is used by sky divers, hikers and mountain climbers.
Do you know?
- Atmospheric-pressure is used for weather forecast.
- The weather is fine when the Atmospheric-pressure is high as 105000 Pa. When it falls to low, about 92000 Pa, there is a probability of a storm.