The force caused by molecules in the atmosphere pressing down on the Earth's surface.

The force caused by molecules in the atmosphere pressing down on the Earth's surface.

• A. Air Pressure
• B. Source
• C. Mouth
• D. Alluvium

Answer: (A)

Air pressure is the force per unit area exerted by the atmosphere on the Earth's surface. The atmosphere is made of moving gas molecules; as they collide with the surface, they push on it. The weight of the air above us creates this pressure, so a thicker column of air (as at lower altitudes) means higher pressure, while at higher elevations the pressure is lower. We measure it with devices like barometers, and typical sea-level pressure is about 1013 hPa (or 101,325 Pa). The other terms don’t describe this force: they aren’t related to the pressure exerted by the air on the surface.

Air pressure is the force per unit area exerted by the atmosphere on the Earth's surface. The atmosphere is made of moving gas molecules; as they collide with the surface, they push on it. The weight of the air above us creates this pressure, so a thicker column of air (as at lower altitudes) means higher pressure, while at higher elevations the pressure is lower. We measure it with devices like barometers, and typical sea-level pressure is about 1013 hPa (or 101,325 Pa).

The other terms don’t describe this force: they aren’t related to the pressure exerted by the air on the surface.