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Air Pressure

Air Pressure. Does Air Have Mass?. Air consists of atoms and molecules, which have mass. Because air has mass, it also has other properties, including density and pressure. Density is the amount of mass in a given volume.

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Air Pressure

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  1. Air Pressure

  2. Does Air Have Mass? • Air consists of atoms and molecules, which have mass. • Because air has mass, it also has other properties, including density and pressure.

  3. Density is the amount of mass in a given volume. You can calculate the density of a substance by dividing its mass by its volume. Density = mass volume Do you recall density?

  4. Air Pressure • The force pushing on an area or surface is known as pressure. The weight of the atmosphere exerts a force on surfaces. • Air pressure is the result of the weight of a column of air pushing down on an area.

  5. Why Doesn’t Air Pressure Crush You? • The molecules in air push in all directions - down, up, and sideways. • The air pushing down is balanced by the air pushing up. The air pushing toward the left is balanced by the air pushing toward the right.

  6. A barometer is an instrument that is used to measure air pressure. There are two types of barometers: mercury barometers and anaeroid barometers. Mercury barometers work as air pressure pushes down on the surface of the mercury dish causing the mercury in the tube to rise. Aneroid Barometer does not contain liquid but has a metal chamber. The metal chamber is sensitive to changes in the air pressure. When air pressure increases the walls of the chamber are pushed in. When air pressured decreases the walls of the chamber bulges out. Measuring Air Pressure

  7. Units of Air Pressure • Inches of Mercury • Millibars • Most weather reports uses inches of mercury. If the column in a mercury barometer is 30 inches high, then the air pressure is “30 inches of mercury”. • The National Weather Service maps indicate air pressure in millibars. One inch of mercury is approximately 33.87 millibars.

  8. Altitude and the Properties of Air • Altitude, or elevation, is the distance above sea level, the average level of the surface of the oceans. • Air pressure decreases as altitude increases. As air pressure decreases, so does density. • Air pressure is greater at sea-level. • Air pressure near the top of the atmosphere has less air pressure.

  9. Altitude and Density • As you go up through the atmosphere, the density of the air decreases. The air molecules that make up the atmosphere are farther apart at high altitudes than they are at sea level.

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