diagram explanation: written explanation: can demonstration

• Diagram Explanation:

• Written Explanation:

Can Demonstration

• A barometer is used to measure air pressure.– Mercury Barometers– Aneroid Barometers

Measuring Air Pressure

• The first barometers.

• Pressure pushes on the surface of the mercury.

• When pressure increases the mercury rises up the tube.

• When pressure decreases the mercury falls in the tube.

Mercury Barometer

• Which barometer shows a higher pressure?

• Which barometer shows a lower pressure?

Feeling the Pressure

• “without liquid”

• Uses an air tight metal chamber.

• The chamber is sensitive to changes in air pressure.

Aneroid Barometer

• Weather Reports use inches of mercury.

• National Weather Service Maps use millibars.

• 1 inHg = 33.87 millibars

Units of Air Pressure

Air Pressure and Density

• Altitude – elevation• Air pressure is the

weight of a column of air pushing down on an area.

• Where is the pressure greater/less?

Altitude Affects Pressure

• Less weight at the top- so there is lower air pressure.

• Sea-level has the weight of the whole atmosphere on it.- Pressure is greatest here.

Altitude Affects Pressure

• As you increase in altitude, the density of air decreases.

• Air pressure decreases as altitude increases.

• As air pressure decreases so does density.

Altitude Affects Density

• As you go up, there are fewer molecules.

• However: The percent of a gas in the atmosphere always stays the same at any altitude.– 78% Nitrogen– 21% Oxygen

Altitude Affects Density

Isobar Maps

• Lines connect areas of __________pressure.

Rules for Drawing Isobars

• Set an interval that is appropriate for the change in pressure.

• Make sure all points on one side of a line are higher and lower on the other.

Sunny(Happy)Weather

Cloudy(Lousy)

Weather

Practice Drawing Isobars

. 1008

. 1006

. 1005

. 1008

. 1008

. 1006

. 1004 . 1003

. 1007

. 998

. 1004

. 1002

. 1001

. 1007

. 1005

. 1002

. 1002

. 1003

. 1007

. 1004

. 1005

.998

.996

.1000

.1012

.1013

.1007

.1000.1000

.1009

.1015

.1004

.1010

.1020

.1005

Practice Drawing Isobars

Draw Isobars on the diagram below. Mark the center of low pressure and high pressure with an H and L.

Interval = ___________________

Drawing Isobars

• Isobars connect lines of equal pressure.

Isobar Maps on RHW

Sunny(Happy)Weather

Cloudy(Lousy)

Weather