# Atmospheric Pressure

### Atmospheric Pressure

1. On the surface of the earth, there is a thick layer of gas called the atmosphere. The atmosphere consists of various types of gas called the atmospheric gas.
2. The atmospheric gases collide on the surface of the earth and hence exert a pressure on the surface of the earth, called the atmospheric pressure.
3. The atmospheric pressure can be measured in the unit of atm, mmHg or Pa. The atmospheric pressure at sea level is taken to be 1 atm, which is approximately 760 mmHg or 101,000 Pa.

### Characteristics of Atmospherics Pressure

1. Decreases with altitude
The atmospheric pressure changes accordingly to the altitude. Altitude is the height above sea level. The greater the altitude, the lower the atmospheric pressure.
2. Act equally in all direction
The atmospheric pressure acts on every object in the atmosphere. It acts equally in all direction.
3. Atmospheric pressure is ~ 100,000Pa at sea level
On the surface of the earth, the atmospheric pressure can be as high as 101,000 Pa.

### Unit Used to Measure Atmospheric Pressure

1. The following are the unit used to measure atmospheric pressure
1. Pascal (Pa)
1 Pa = 1 N/m²
2. Standard Atmospheric Pressure (atm)
1 atm = Atmospheric Pressure at sea level ( = 101,325 Pa)
3. mmHg (also known as torr)
1 mmHg = 1/760 atm (roughly equal to the liquid pressure exerted by a millimetre of mercury).
4. milibar (Not used in SPM)
2. In SPM, usually we use the unit cmHg, instead of mmHg.