Chapter 1, Section 3 Pages 25-30 AIR PRESSURE Chapter 1, Section 3 Pages 25-30

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.

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

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 vacuum…there is NO air in there! As air pressure increases, the level of the fluid in the tube increases and visa-versa.

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.

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

What is altitude? Altitude, or elevation, is the distance above sea level, the average level of the surface of the oceans.

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.

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.)