Water Is essentIal Water is the most important liquid on Earth Nearly three-fourths of Earth’s surface is covered with water All plants and animals need water to live Water exists in many different forms such as salt water in oceans and freshwater in rivers or lakes Other examples include frozen water of glaciers or water found deep in the ground The amount of water on the planet remains the From outer space Earth appears to be mostly blue because of the water that covers most of its surface 4
People use water for a wide range of everyday tasks including washing dishes same but it constantly moves around The way water moves around Earth is called the water cycle People have many uses for water besides drinking They use it for washing and cooking They use it to irrigate crops and lawns to clean streets and to operate air-conditioning units and heating systems They also use the power of flowing water to produce electricity Compare and Contrast How are oceans and rivers alike In what ways are they different 5
states and Forms Water is made of tiny units called molecules which are combinations of even smaller units called atoms A molecule of water is made of two hydrogen atoms and 6 Vocabulary Atoms are tiny particles Atoms are the building blocks of all matter Shown here are three ways to represent a water molecule and the atoms within it
This glass of ice water contains two physical states of water liquid and solid one oxygen atom The scientific formula for water is H2O Water makes up about 60 percent of an adult’s body weight Water helps the body get rid of waste and maintain its temperature Water can be found in three physical states liquid solid ice or gas steam or vapor The molecules in all three states are constantly moving In snow or ice the water molecules vibrate but basically stay in place In rain the molecules move more quickly but stay near each other But in steam the molecules move so quickly that they fly away in all directions 7
