AIR PRESSURE

1
AIR PRESSURE

• Chapter 1, Section 3
• Pages 25-30

2
What properties does air have?

• Since it is made of atoms and molecules, which
  are made of matter, air must have
• Mass
• Volume
• Density
• Pressure- the force pushing on an area or surface.

3
What is AIR PRESSURE? How is air pressure
measured?

• Air pressure is the result of the weight of a
  column of air pushing down on an area.
• That weight is measured with a barometer.
• HIGH PRESSURE- fair weather or a clear sky
• LOW PRESSURE- storm is approaching or a cloudy sky

4
What is a Mercury barometer?

• A mercury barometer consists of a glass tube open
  on the bottom end and partially filled with
  mercury.
• The empty space in the tube is a vacuumthere
  is NO air in there!
• As air pressure increases, the level of the fluid
  in the tube increases and visa-versa.

5
What is an aneroid barometer?

• An aneroid barometer is an instrument that
  measures air pressure without liquid.
• It consists of an airtight metal chamber
  sensitive to slight changes in air pressure.
• As pressure increases, the thin walls push in and
  cause the dial, which is connects to springs,
  indicate an increase in pressure and visa-versa.

6
What are the two units used to measure air
pressure?

• Inches of mercury and millibars
• Average air pressure is
• 1013.25 millibars
• 29.92 inches

7
What is altitude?

• Altitude, or elevation, is the distance above sea
  level, the average level of the surface of the
  oceans.

8
How does altitude affect air pressure? WHY?

• Air pressure decreases as altitude increases.
• A larger column of air has more molecules
  within it and creates more force than a smaller
  column of air.
• As altitude increases the column or air gets
  smaller and smaller.

9
How does the density of air change as altitude
increases?

• As altitude increases, air pressure decreases and
  so does density.
• If the air is LESS DENSE, then that means that
  there are FEWER molecules to create the force of
  pressure (air pressure.)