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PROPERTIES OF THE ATMOSPHERE
TEMPERATURE
• Temperature is the measure of the average kinetic energy of the particles in a material.
• Higher temperature means particles are moving faster.
• Temperature Scales• Fahrenheit (used in United States)
• Celsius (used in the rest of the world)
• Kelvin (SI unit of temperature)
• The Earth’s atmosphere, because air has weight, exerts pressure.
• Density of air decreases as altitude increases so pressure also decreases.
AIR PRESSURE
PRESSURE-TEMPERATURE-DENSITY
• Air Pressure versus Temperature• At the same density, warm air exerts more pressure than
cooler air.
• Air Pressure and Density• At the same temperature, more dense air exerts more
pressure.
• Temperature and Density• At the same pressure, warm air is less dense than cool air.
HUMIDITY
• Humidity is the amount of water vapor in the atmosphere at a given location.
• Two ways to express water vapor content:• Relative Humidity
• Dew Point
RELATIVE HUMIDITY
• The amount of water in a volume of air relative to the amount of water vapor needed for that volume of air to reach saturation is called relative humidity.
• The dew point is the temperature to which air must be cooled at constant pressure to reach saturation.
• When temperature falls to this level, dew begins to forms (condensation).
• If the dew point is nearly the same as the air temperature, then the relative humidity is high.
DEW POINT
SAMPLE CALCULATION
• What is the relative humidity of 1 kg of air containing 20 g of water at 40 °C?
• There can be up to 50 g of water in a 40 °C sample.
• (20g/50g) x 100 = 40% relative humidity
CLASS ACTIVITIES
• Complete the Mini Lab on page 295 and answer the Analysis questions on your own sheet of paper.
• Complete the Problem-Solving Lab on page 294 and answer the Think Critically questions on the same sheet of paper.
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