9781422280539

water

P hysical S cience For all its importance, a water molecule is remarkably simple in design: three atoms—two hydrogen (H) and one oxygen (O)—which is why you might have heard it referred to as “H 2 O.” The chemical bonds in water give it its cohesive quality, meaning that it sticks together. This is why water has a skin-like surface that insects like water striders can float on (as can objects such as paper clips—try it!). It’s also why water does not come apart when trees suck it all the way up from their roots to their leaves. Water is the only substance that occurs naturally as a liquid at Earth’s normal temperature. It’s also the only one that can take the form of a solid, liquid, or gas. The ability to move between these three forms within the narrow range of Earth’s temperatures and pressures means that water is continually passing through the hydrologic cycle : evaporating from bodies of water as vapor, forming into clouds (a process called condensation ), and falling again as precipitation, either rain or snow. This cycle supplies freshwater to all the Earth’s animals and plants and transports nutrients to aquatic ecosystems. The hydrologic cycle has a direct Educational Video

influence on our weather and climate. As the sun warms the ocean and causes water to evaporate, heat is stored in the vapor. When the vapor cools into clouds, this heat is released into the air. This cycle helps move heat from the ocean’s surface into the atmosphere and eventually around the globe. Ocean currents distribute heat, too. From the equator, where the sun’s rays hit Earth most directly, currents move warm

The Great Aqua Adventure

Check out this video about the water cycle.

14