Pressure and Atmospheric Pressure

Pressure

• Pressure is defined as the force per unit area in a gas or a liquid, and it is referred to as stress in solids.
• The formula for pressure is P = F/A, measured in units of N/m² or dynes/cm².

Atmospheric Pressure

• Atmospheric pressure is due to the weight of the air in the atmosphere.
• 1 atm is equal to 101325 N/m², 105 N/m², or 105 Pa.
• 1 atm is also equal to 760 mmHg.

Units of Pressure

• Units of pressure can be atm, Pascal (Pa), N/m², or dynes/cm².
• In medicine, the unit of pressure is measured by the height of a column of mercury (Hg).
• 1 Pa (Pascal) is equal to 1 N/m².

Pressure under a Column of Liquid

• Pressure under a column of liquid is given by the formula P = ρgh.
• ρ is the density of the liquid, g is the acceleration due to gravity, and h is the height of the column.

Measurement of Body Pressure

• Pressure is a common phenomenon in daily life, and doctors measure blood pressure as part of a physical examination.
• The peak systolic pressure is 120 mm Hg, which is equivalent to a pressure of a liquid mercury of this height on its base.
• The atmospheric pressure is equal to 760 mm Hg.

Typical Pressures in the Body

• Arterial blood pressure: 100-140 mm Hg (maximum/systolic), 60-90 mm Hg (minimum/diastolic).
• Venous blood pressure: 3-7 mm Hg.

Sphygmomanometer

• Not mentioned in the provided text, but it is a device used to measure blood pressure.