Chapter 6 Air Pressure

Gale Force Winds Create Waves that Batter Coast in UK in 2002

What are the Basic Elements of Weather & Climate (list 6) Wind Temperature Humidity Clouds Precipitation Pressure

Objectives (pg. 169) 1.Define air pressure. 2. The units of force used to measure it. 3.Discuss how a mercury barometer and an aneroid barometer measure air pressure.

Bell work How many pounds of pressure do you exert on Earth? 1.Measure the sole of your shoe: L x W to get the AREA of your shoe in inches 2 2. Multiply x 2 shoes. 3. Divide your weight in lbs. area of your shoes 4. How many pounds of pressure do you exert on Earth? __________ lbs./in 2

Air pressure is …(pg. 168) The pressure exerted by the weight of the air above. Weight is a FORCE, a push or pull. You don’t “feel” it because the pressure on you is balanced. You feel it when it changes and your ears ‘pop’ as in a rapidly dropping airplane or elevator.

Average Air pressure at sea level cm 3 Column of water 33 ft. high

Ocean of Air around us

We are surrounded by an “ocean” of air. Gas molecules are free to move – filling all the space available At the surface = 1 ATM Pressure 5 km altitude = 50% ATM 10 km = 25% ATM Denver, CO the ‘mile high city’ = 82% ATM

1. Which has MORE PARTICLES? 2. Which is more DENSELY packed? 3. Which has more COLLISIONS? 4. Which is exerting HIGHER PRESSURE? 5. Which has a colder TEMPERATURE?

When gas molecules collide, they bounce off each other, exerting an outward pressure The force exerted against a surface by a continuous collision of gas molecules.

Measuring Air Pressure Unit for force in physics is Newton (N) At sea level the atmosphere exerts a force of 101,325 newtons/meter 2 U.S National Weather Service 1940, Millibar: (mb) = 100 newtons/m 2 Standard sea-level pressure is mb

Measuring Atmospheric Pressure Mercury Barometer 1643 Torricelli When air pressure increased, the mercury in the tube rose up - increased

Comparing Atmospheric Pressures in mb

Aneroid Barometer (without air) High pressure readings (>30) indicates _________ weather, and low pressure readings (<30) indicates ________ weather Barograph

Associated Weather… …with High Pressure …with Low Pressure

Adjusting to Sea-Level Pressure by adding the pressure that would be exerted by an imaginary column of air to the stations pressure reading.

Isotherms: lines of same TEMPERATURE

Isobar- lines connecting areas of equal PRESSURE

L H Locate the areas of the highest and lowest pressure H

Draw isobars for each of the following measurements 1004, 1008, 1012, 1016, 1020

Draw Isobar lines at 1008, 1012, 1016, 1020, 1024