User:DrOwl/Science notes

1. The Water Cycle

• When ice gains thermal energy, it changes from its solid state into its liquid one. This process is known as melting.

• Sometimes, when thermal energy is added to ice, it changes its state from solid to gas, rather than solid to liquid. This is called sublimation.

• When water absorbs enough thermal energy, it becomes a gas, evaporating.

• When water vapor loses thermal energy, it becomes liquid water. This is called condensation.

• When water vapor loses all of its thermal energy, it becomes ice. This is called deposition, and it is the opposite of sublimation.

• When liquid water loses thermal energy, it freezes, becoming solid ice. 2. Watersheds

Great lakes basin.jpg • A watershed is an area of land where all of the water that falls into it and drains off of it goes to the same place.

• Watersheds can be of very varying sizes.

• Watersheds can be in almost any type of environment. Toronto has seven river watersheds, each of which drains into Lake Ontario, which itself is part of the Great Lakes Basin watershed.

• Watersheds have three main goals: capturing water, filtering and storing water in soil, and releasing the water into a body of water.

• The two types of watersheds are open and closed.

• An open watershed drains into the ocean, while a closed watershed can only escape by evaporating or seeping into the ground. 3. Water Treatment and Quality

Illustration of a typical drinking water treatment process.png • Fresh water contains dissolved substances that make it unsafe for us to drink.

• Water treatment is the process of making water safe for its desired use.

• Step 1: A metal screen is used to cover the end of the pipe that draws the water. The water is able to go through the screen, but any large objects are not.

• Step 2: In a large tank, a chemical called alum is added to the water. The alum forms small, sticky lumps; attracting most of the waste in the water. These clumps are known as floc.

• Step 3: The water and floc then enter a settling tank, allowing the floc to settle at the bottom.

• The treated water is stored in sealed containers.

• Reverse osmosis is a process in which mechanical pressure is used to force water through a membrane, which acts as a fine filter.

• Ultraviolet radiation can effectively destroy most viruses and micro-organisms. It is used when it is particularly important that water be free of organisms and virus, such as the water supply for a hospital.

• In nature, water absorbs calcium and magnesium from surrounding rock. This makes the water "hard", which is safe to drink, but when heated leaves mineral deposits. We have water softeners that remove the hardness from water. 4. Water Table

Water table.svg • A water table is the boundary between ground that is saturated with water and unsaturated ground.

• Water tables in certain areas can fluctuate as water seeps down from the surface.

• Geology, weather, land use, and ground cover all influence the water table.

• Geology influences it because lighter rocks can hold more water than heavier and denser ones.

• Weather influences it because the water table will usually be higher in rainy seasons or in early spring when the snow melts.

• Land use influences it because urban areas have surfaces that do not allow water to pass through. This water becomes runoff and the water table dips.

• Ground cover influences it because the vegetation in swamps are always saturated for at least part of the year, so water tables in swamps are almost always level with or higher than the surface.

• Humans draining aquifers for personal, agricultural, and industrial use if causing some water tables to drop very quickly.

• Natural factors also influence water tables; such as storms, floods, rain, droughts, snow, ice, and the changing seasons. 5. Glaciers and Polar Ice

Arctic sea ice loss animation.gif • The majority of fresh water on Earth is in ice.

• Ice is found on many mountain tops and covers polar regions.

• As one moves away from the poles (towards the Equator), the number of months in which it snows decreases.

• When snow does not melt in Spring, it continues to accumulate every year. The top layers of snow press down on the lowers ones, slowly turning them into ice. This is how glaciers, icecaps, and polar ice sheets are formed.

• Water temperatures increase when the oceans absorb more of the Sun's energy.

• Warm water is less dense than cool water. As ocean temperature rises, this warm water takes up more spaces, making the sea levels rise. Warm water also warms the air above it.

• The warm air created by the water circulates around the planet, warming polar regions and melting polar ice.

• As the polar ice melts, the melted water flows into the oceans, further raising the sea levels.

• The Great Lakes, a series of interconnected lakes in midwestern North America, hold one-fifth of the world's freshwater.