What is atmospheric pressure?

Atmospheric pressure is the pressure exerted by the weight of the air column above any surface.

• At sea level: 1 atm = 101,325 Pa = 760 mm Hg
• Measured by a barometer.
• Decreases with altitude less air above = less weight = less pressure.

Everyday effects: Drinking through straws, suction cups, mercury rising in barometer, breathing difficulty at high altitude.

Atmospheric pressure is the force per unit area from Earth's air column, equal to 101.3 kPa at sea level and decreasing with altitude.