Air Pressure Defined as the force exerted on

  • Slides: 30
Download presentation

Air Pressure • Defined as the force exerted on you by the weight of

Air Pressure • Defined as the force exerted on you by the weight of tiny air particles in the atmosphere per unit area. – Earth’s atmospheric pressure = 14. 7 pounds per square inch OR 1 kilogram per square centimeter

Mercury Barometer • Invented by Evangelista Toricelli (early 1600 s). First scientist to use

Mercury Barometer • Invented by Evangelista Toricelli (early 1600 s). First scientist to use mercury barometer to measure atmospheric pressure changes. – Inverted glass tube filled with mercury placed in a dish of mercury. – Mercury will flow from the tube to the dish until the weight of mercury is equivalent to the air pressure on the mercury dish. – 29. 92 in Hg = 760 mm Hg

Aneroid Barometer • Invented by Lucien Vidie (1843). “Aneroid” means fluidless. Registers the change

Aneroid Barometer • Invented by Lucien Vidie (1843). “Aneroid” means fluidless. Registers the change in shape of a metal capsule (expanding and contracting) to measure atmospheric pressure.

Air Pressure • Millibars comes from the original term for pressure "bar". Bar is

Air Pressure • Millibars comes from the original term for pressure "bar". Bar is from the Greek "báros" meaning weight. – 29. 92 in Hg = 1013. 25 mb (millibars) <<< Average Sea Level Pressure

High Pressure – Isobar readings increase towards an area. – Winds move clockwise (anticyclone).

High Pressure – Isobar readings increase towards an area. – Winds move clockwise (anticyclone). – Fair weather conditions – no precipitation.

Low Pressure – Isobar readings decrease toward an area. – Winds move counter clockwise

Low Pressure – Isobar readings decrease toward an area. – Winds move counter clockwise (cyclone) – Bad weather conditions – precipitation.

Air Pressure Systems • Isobars – lines on a map that show equal air

Air Pressure Systems • Isobars – lines on a map that show equal air pressure. – Recorded in millibars (mb). • Air pressure will change due to changes in air temperature and humidity. • Wind blows from High Pressure systems to Low pressure systems.

Pressure Gradient Force (PGF) • Lines that are close together indicate a strong pressure

Pressure Gradient Force (PGF) • Lines that are close together indicate a strong pressure gradient force – High winds. • Lines that are far apart indicate a weak pressure gradient force – Light winds. • WINDS ALWAYS BLOW FROM HIGH PRESSURE TO LOW PRESSURE.

strong weak

strong weak