I. Air Pressure 19.1 Understanding Air Pressure  A)  A) The pressure exerted by the weight of air.  B)  B) Air pressure is exerted in all directions. Pressure pushing down on an object exactly balances the air pressure pushing up on the object.

II. Measuring Air Pressure 19.1 Understanding Air Pressure  A) Barometer is a device used for measuring air pressure.

A Mercury Barometer

III. Factors Affecting Wind 19.1 Understanding Air Pressure  A) Wind = horizontal differences in air pressure. In general Air flows from areas of H pressure to areas of L pressure.

III. Factors Affecting Wind 19.1 Understanding Air Pressure  1) Pressure Differences a) a) pressure gradient = amount of pressure change occurring over a given distance. (Isobars)

Isobars

III. Factors Affecting Wind 19.1 Understanding Air Pressure  2) Coriolis Effect a) a) describes how Earth’s rotation affects moving objects. b) b) In the N. Hemi, all free-moving objects are deflected to the right. In the S. Hemi, they are deflected to the left.

The Coriolis Effect

III. Factors Affecting Wind 19.1 Understanding Air Pressure  3) Friction a) a) slows air movement, which changes wind direction. b) b) Jet streams 1) 1) fast-moving rivers of air that travel between km/ hr. from west-to-east.

Effect of Friction