6th Grade Science
Atmosphere in Motion
Unit 3 Study Guide
12.1 The Atmosphere
 The atmosphere is made of gases, liquids and solids
o Solids = aerosols (tiny particles of dust, salt, and pollen)
o Nitrogen and oxygen are the most abundant gases
 Water circulates between Earth’s surface and the atmosphere in the hydrologic cycle
o Evaporation- liquid water changes into water vapor
o Condensation- water vapor comes together to form liquid droplets
o Precipitation- liquid droplets too heavy to remain in cloud
o Transpiration- liquid water escapes from plants turns into water vapor
 How is the Sun involved in the water cycle?
Key terms: atmosphere, aerosol, troposphere, water cycle
12.2 Earth’s Weather
 Factors that determine the weather:
o Sun
o Temperature- average motion of air particles
o Humidity- amount of moisture in the air
o Air pressure- as altitude increases, pressure decreases because less particles to
push down
o Wind- movement of air from area of high to low pressure
 How does temperature influences the type of precipitation?
 Warm air holds more water vapor than cold air
 What is the relationship between air pressure and temperature?
 What causes wind?
 Earth’s rotation causes the Coriolis effect
 The difference in radiation (temperatures) and the Coriolis effect combined produce
global winds
o Doldrums- windless zone near the equator
o Trade winds- steady winds directly outside the equator
o Prevailing westerlies- affect the weather in the United States
o Polar easterlies- air currents that blow near the north and south poles
Key terms: weather, humidity, dew point, relative humidity, precipitation
12.3 Air Masses and Fronts
 Air masses are dry or moist and warm or cool, depending on the location of the surface
they cover
 Fronts develop where air masses of different temperatures meet
 Four types of fronts:
1. Warm- warm air moves in slowly over cool air; creates long, steady
precipitation
2. Cold- cool air moves in quickly and forces warm air up; creates heavy rain and
violent storms
3. Occluded- warm air is cut off by cool and cold air and forced up
4. Stationary- warm and cool air at standstill
 What do all four types of fronts have in common?
 Blizzards form during freezing temperatures when snow falls to the ground at fast speeds
o Dangerous because decreases visibility
 Both thunderstorms and tornadoes form from a cold front (cumulonimbus clouds)
 Hurricanes form from swirling winds over tropical oceans (warm, moist air)
Key terms: air mass, front, tornado, hurricane
Short answer questions:
1. Weather factors
2. Fronts