increasing thermal energy of particles sublimation melting freezing deposition decreasing thermal energy of particles requires energy (heat)

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1 10.3 The Water Cycle Key Question: How does water move through the water cycle? You may see water as ice, snow, rain, and steam. On very humid days, you can sense it as water vapour. Water is the only substance that exists on Earth in its three states. CHANGES OF STATE Water changes state when it gains or loses thermal energy. Figure 1 shows how water particles behave when they change state. increasing thermal energy of particles melting evaporation solid gas decreasing thermal energy of particles requires energy (heat) releases energy (heat) Figure 1 Water gains or as it changes state. melting from a solid to a liquid; occurs when a solid from a solid to a gas without first becoming a liquid; occurs when a solid 214 Chapter 10 Worksheet Water changes state in six different ways: melting: When ice absorbs enough thermal energy, it changes to liquid water. For example, ice cubes melt in a drink. : Sometimes the addition of thermal energy causes ice to change to a gas without becoming a liquid first. For example, snow may seem to disappear without melting into puddles.

2 evaporation from a liquid to a gas; occurs when a liquid from a liquid to a solid; occurs when a liquid from a gas to a liquid; occurs when a gas from a gas to a solid; occurs when a gas evaporation: When liquid water absorbs enough thermal energy, it changes to water vapour. For example, wet clothes on a washing line dry because the water evaporates into the air. : When liquid water loses enough thermal energy, it changes to ice. For example, ponds and lakes freeze in cold weather. : When water vapour loses enough thermal energy, it changes to liquid water. For example, water vapour condenses on cool grass to form dew. : Sometimes the loss of thermal energy causes water vapour to change directly to a solid. For example, water vapour creates ice in the form of frost on cold windows. water cycle a continuous pattern in nature in which water moves as it changes state above, on, and below the of Earth (water storage in ice and snow) THE WATER CYCLE Water changes state in a continuous pattern called the water cycle. The water cycle is powered by the Sun. It moves water around Earth (Figure 2). cloud formation (water storage in the atmosphere) precipitation runoff (snowmelt into streams) ice Sun water vapour evaporation water runoff Figure 2 Water changes state in a pattern called the water cycle. Chapter 10 Worksheet TURN

3 MELTING, EVAPORATION, AND SUBLIMATION Melting, evaporation, and happen when water particles gain enough thermal energy. Melting Solid water exists in winter as ice and snow. It also exists as permanent ice and snow in glaciers and polar regions. When ice and snow absorb enough thermal energy, they melt to form liquid water. Liquid water also falls to the ground as rain. The water from ice and snow, together with rain, flows to different places. runoff water from precipitation and snowmelt that flows over Earth s water that seeps through soil and cracks in rock; the source of water for underground springs and wells aquifer a geological formation of loose rock or soil that is saturated with Some liquid water becomes runoff. Runoff flows over Earth s to rivers, lakes, and oceans. All of the liquid water on the of Earth is called water. Some liquid water flows down through openings in soil and rock until it hits bedrock. Once the liquid water hits bedrock, it cannot flow down any farther. This water is called. Groundwater fills, or saturates, the spaces in the rock and soil above the bedrock. This saturated area is called an aquifer (Figure 3). The top of the aquifer is the water table. water table the depth at which loose rock and soil below Earth s are saturated with water; the upper boundary of an aquifer soil water table aquifer water bedrock Figure 3 Groundwater saturates loose rock and soil to form an aquifer. 216 Chapter 10 Worksheet

4 Evaporation and Sublimation Solid and liquid water on the of Earth move back into the atmosphere as water vapour. Water vapour forms in two ways: water evaporates snow and ice sublime Water vapour in Earth s atmosphere acts like a blanket. It traps thermal energy close to Earth. CONDENSATION, DEPOSITION, AND FREEZING Condensation,, and happen when water particles lose enough thermal energy. Condensation and Deposition When water vapour in the atmosphere loses thermal energy, it can condense into water droplets. It can also undergo to form ice crystals. Water droplets and ice crystals in the atmosphere form clouds (Figure 4). Figure 4 Water vapour forms clouds through and. precipitation solid or liquid water that falls to Earth s These cloud particles fall to the ground as precipitation. Water droplets collide with each other to form larger droplets. These large droplets fall as rain. Ice crystals fall as snow. Chapter 10 Worksheet TURN

5 Name: Date: polar ice sheet a frozen field of ice covering either the North Pole or the South Pole icecap a large area of ice that permanently covers land glacier a river of ice, formed from snow accumulated over hundreds of years, that moves slowly downhill under the force of gravity When snow falls, it may accumulate on Earth in different ways: as polar ice sheets: areas of ice at the North and South Poles as ice caps: permanent ice that covers land as glaciers: rivers of ice that slowly flow down mountains Freezing In cold temperatures, Earth s water freezes and forms solid ice. Ice is slightly less dense than liquid water. For this reason, a layer of ice forms on top of the liquid water in lakes and ponds. The organisms in the water below the ice do not freeze solid. CHECK YOUR UNDERSTANDING 1. What causes water to change state? 2. What happens to liquid water after it seeps into the ground? 3. How do solid and liquid water change to water vapour? 4. How does water in Earth s atmosphere return to Earth s? 5. Think back to the Key Question. Name three ways you can see the water cycle in action in your community. 218 Chapter 10 Worksheet END