S 6.2 Topography is reshaped by the weathering of rock and soil and by the transportation and deposition of sediment. As a basis for understanding this concept: d. Students know earthquakes, volcanic eruptions, landslides, and floods change human and wildlife habitats. S 6.4 Many phenomena on Earth's sur­ face are affected by the transfer of energy through radiation and convection currents. As a basis for understanding this concept: a. Students know the sun is the major source of energy for phenomena on Earth's surface; it powers winds, ocean currents, and the water cycle. e. Students know differences in pressure, heat, air movement, and humidity result in changes in weather. S 6. 7 Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will: e. Recognize whether evidence is consistent with a proposed explanation. g. Interpret events by sequence and time from natural phenomena (e.g., the relative ages of rocks and intrusions). h. Identify changes in natural phenomena over time without manipulating the phenomena (e.g., a tree limb, a grove of trees, a stream, a hillslope). Which weather factors produce changes in weather? Check What You Know Think about the last time you took a hot shower. You may have noticed when you got out that the mirror was covered with a thin film of moisture. Where do you think this moisture came from? How did it get there? Would the same film of moisture appear if you took a cold shower? Why or why not? The images shown here represent some of the key terms in this chapter. You c~n use this vocabulary skill to help you understand the meaning of some key terms in this chapter. Identify Multiple Meanings Some words have more than one meaning. Words you use everyday may have different meanings in science. Look at the different meanings of the words below. Word I Everyday Meaning I Scientific Meaning cyclone n. A windstorm with a violent n. A center of low air pressure whirling movement; a tornado Example: The forecaster said Example: When the cyclone the cyclone would have clouds, touched down, it destroyed light rain, and moderate winds. the barn. front n. The forward part or surface n. The boundary between Example: Enter by the door in two air masses of different , the front of the house, not the temperatures and humidities one in back. Example: Storms often develop along fronts. relative n. A member of your family adj. Having a particular quality Example: Her brother is her compared to something else closest relative. Example: The temperature here is mild relative to the temperature in Alaska. Apply It! Complete the sentences below with the correct word from the list above. Identify the sentence that uses the scientific meaning. 1. A warm will arrive in this area tomorrow. 2. The of the store has a window display of skateboards. (page 300) water cycle evaporation humidity relative humidity psychrometer condensation dew point cirrus cumulus stratus Section 2 (page 307) precipitation (page 310) air mass tropical polar maritime continental front occluded cyclone anticyclone (page 318) storm thunderstorm lightning tornado hurricane storm surge (page 328) meteorologist isobar isotherm ,.; Build Science Vocabulary Online Visit: PHSchool.com Web Code: cwj-3080 Chapter 8 + 297 ,1'-C( l/ !:'i-' Compare and Contrast Science texts often make comparisons. When you compare and contrast, you examine the similarities and differences between things. You can compare and contrast by using a table. Follow these steps to set up a compare/contrast table. • List the characteristics to be compared across the top of the table • List the things to be compared in the left column. • Complete the table by filling in information about each characteristic. In this chapter you will learn the term front, which is the area where unlike air masses meet. There are four types of fronts. Look at Figure 14. Then look at the following table. Front I How Forms I Type of Weather Cold front A cold air mass overtakes a warm air mass. Warm front Stationary front Occluded front Apply It! Answer the following questions in complete sentences. 1. What are the items being compared in this table? 2. What are the characteristics that are being compared? 3. How does a cold front form? After reading Section 2, make a compare/contrast table for types of precipitation. Complete the compare/contrast table above after you read Section 3. The Weather Tomorrow When the sky turns dark and threatening, it's not hard to predict the weather. A storm is likely on its way. But wouldn't you rather know about an approaching storm before it arrives? In this investigation, you will get a chance to make your own weather forecasts and compare them to the forecasts of professionals. Good luck! Your Goal Predict the weather for your own community and two other locations in the United States. To complete this investigation you must • compare weather maps for several days at a time • look for patterns in the weather • draw maps to show your weather predictions Plan It! Begin by previewing the chapter to learn about weather maps and symbols. Start a project folder to store daily national weather maps and a description of the symbols used on the maps. Choose two locations that are at least 1,000 kilometers away from your town and from each other. As you collect weather maps, look for patterns in day-to-day weather changes. Then predict the next day's weather and compare your predictions to the professional forecasts and to the actual weather. 4tl( Section 1 Water in the Atmosphere -. How Does Fog Form? 5 6.4.a Students know the sun is the major source of energy for phe­ 1. Fill a narrow-necked plastic bottle with hot tap nomena on Earth's surface; it pow­ water. Pour out most of the water, leaving ers winds, ocean currents, and the about 3 em at the bottom. CAUTION: Avoid -«: water cycle. spilling hot water. Do not use water that is so S 6.4.e Students know differences hot that you cannot safely hold the bottle. in pressure, heat, air movement, 2. Place an ice cube on the mouth of the bottle. and humidity result in changes in weather. What happens? 3. Repeat Steps 1 and 2 using cold water instead What is humidity and how is it of hot water. What happens? _. measured? Think It Over ~ How do clouds form? Developing Hypotheses How can you explain your ~ What are the three main types of observations? Why is there a difference between what happens clouds? with the hot water and what happens with the cold water? Key Terms • water cycle During a rainstorm, ·the air feels moist. On a clear, cloudless ·.A • evaporation day, the air may feel dry. As the sun heats the land and oceans, • humidity the amount of water in the atmosphere changes. Water is • relative humidity • psychrometer always moving between the atmosphere and Earth's surface. • condensation The continuous movement of water between the atmo­ • dew point sphere and Earth's surface is called the water cycle. The sun's • cirrus energy in the form of radiation powers the water cycle. How­ • cumulus ever, the cycle itself has no real beginning or end. • stratus As you can see in Figure 1, water vapor enters the air by evap­ oration from the oceans and other bodies of water. Evaporation is the process by ·which water molecules in liquid water absorb energy and escape into the air as water vapor. Water vapor is also added to the air by living things. Water enters the roots of plants, rises to the leaves, and is released as water vapor. As part of the water cycle, some of the water vapor in the atmosphere condenses to form clouds. Rain and snow fall from the clouds toward the surface. The water then runs off the sur­ face or moves through the ground, back into the lakes, streams, and eventually the oceans. Humidity How is the quantity of water vapor in the atmosphere mea­ fiGURE 1 sured? Humidity is a measure of the amount of water vapor in Water Cycle · the air. Air's ability to hold water vapor depends on its temper­ In the water cycle, water moves ature. Warm air can hold more water vapor than cool air. from oceans, lakes, rivers, and plants into the atmosphere and Relative Humidity Weather reports usually refer to the then falls back to Earth. water vapor in the air as relative humidity. Relative humidity is the percentage of water vapor that is actually in the air com­ Go~nline pared to the maximum amount of water vapor the air can hold at a particular temperature. For example, at 10°C, 1 cubic active@ meter of air can hold at most 8 grams of water vapor. If there actually were 8 grams of water vapor in the air, then the relative For: Water Cycle activity Visit: PHSchool.com humidity of the air would be 100 percent. Air with a relative Web Code: cfp-4024 humidity of 100 percent is said to be saturated. If the air had 4 grams of water vapor, the relative humidity would be half, or 50 percent. ~ .A( Measuring Relative Humidity ~ Relative humidity can be measured with an instrument called a psychrometer. A psychrometer ( sy KRAHM uh tur) has two thermo­ meters, a wet-bulb thermometer and a dry-bulb ther­ mometer, as shown in Figure 2.