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Chapter 15 Study Guide Name _____________ Text pages 430 - 445 15.1 Atmospheric Pressure and Influences Pressure is defined as the force a Pascal (Pa). exerted on a given area. The unit of pressure is Here are three examples of pressure which you may have experienced: 1. Air pressure in a bicycle or car tire, often measured in psi (pounds per square inch) 2. Weather forecasts, air pressure is reported in kilopascals (1 kPa = 1000 Pa) 3. Lower air pressure at higher altitudes when going up a mountain at Whistler or flying in a plane. Your ears ‘pop’ to equalize the air pressure inside and outside your ear. Atmospheric pressure, or air pressure, is the weight per unit area of the gas particles in the atmosphere due to gravity . At sea level, atmospheric pressure averages 101.3 kPa . A barometer is an instrument that measures air pressure. Atmospheric Can Crusher Demo A pop can has very little water put in it and is then brought to a boil. It is quickly inverted into a beaker of cold water. Describe what happens when the pop can makes contact with the cold water. _______________________________________________________________ _______________________________________________________________ What happens to the energy of the air molecules inside the can once you remove it from the Bunsen burner? How does contact with the cold water affect their energy? _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ Thermal Expansion and Air Pressure According to the kinetic molecular theory , molecules speed up and spread out when heated. This creates a region of lower density, and lower pressure. Density and pressure differences explain why hot air rises and cold air sinks . The sun heats the air near the Earth’s surface. The heated air expands and becomes less dense. It then floats up through the surrounding cooler, denser air. Water vapour mixes with other gases in the atmosphere. As warm air rises , it cools and some water vapour may condense into clouds. Further condensation forms liquid water droplets and rains . A low-pressure cell is an area of lower air pressure at the Earth’s surface formed by a warmed air mass that is expanding and rising. A high-pressure cell is a region of high pressure at the Earth’s surface formed by the sinking of denser air. Isobars are lines of equal atmospheric pressure often shown on weather maps. Uneven surface heating also produces convection currents and winds Weather occurs in the troposphere troposphere, temperature decreases . , the lowest layer of the atmosphere. In the with height. Combining the amount of moisture in the air with our knowledge of the movement of high and low pressure systems, we can predict precipitation. 15.2 Energy Distribution The Earth is warmer concentrated in a smaller area at the equator because the energy of the sun’s rays is . The Earth is colder because the energy of the sun’s rays is spread over a larger area The reason for the seasons is the tilt of the Earth’s axis strike an area in the summer than in the winter. at the poles . . More rays Sea and Land breeze Water has a higher heat capacity than sand. This means that water heats up more slowly and it stays warm longer. The resultant pressure difference then produces winds or breezes. A) Sea breeze (day) Air over the land heats up faster . It expands, rises and creates a low pressure zone. The cooler denser air over the water blows over the land. The reverse happens during the night. B) Land breeze (night) Air over the land cools faster . It becomes denser and creates a high pressure zone. The dense air over the land replaces the less dense air over the water. A tornado is a rapidly rotating wind that forms within a thunderstorm. It forms when hot humid air is covered above by cool dry air. Most tornadoes are 100 to 600 m in diameter, with wind speeds of 125 to 400 km/h. Tornadoes typical last only a few minutes but can travel several kilometers. 15.3 Global Patterns of Wind and Water Prevailing Winds are winds that blow in a consistent pattern over large portions of of the Earth’s surface by the the globe. They are caused by uneven heating sun . This creates two large-scale convection currents at the equator, called Hadley cells . The Earth’s rotation does NOT create winds, but it does affect their direction. Jet Streams are narrow bands of high-speed westerly winds that occur near the top of the troposphere. The Coriolis Effect explains the why the Earth’s rotation trajectory of an object to appear deflected . See http://www.youtube.com/watch?v=mcPs_OdQOYU causes the Ocean currents are also created from prevailing winds. Like blowing on the surface water in a glass, friction between the winds and the ocean produces surface flows. Ocean currents can transport thermal energy from the equator to the poles. The currents affect the temperature of the air blowing above them, which influences weather such as tropical storms and El Nino .