What are the properties of water? How does water change from one form to another? How can temperature of solids and liquids be measured?

Water is unique in that it is the only natural substance that is found in all three physical states—liquid, solid, and gas—at the temperatures normally found on Earth. 

Objects and substances can be classified by their properties.  The common substance, water, has the physical of occurring naturally in three states:  ice, water, and water vapor.  Water can change state when it is heated or cooled (when heat energy is added or lost).  Water freezes at 32° Fahrenheit (F) and boils at 212°F.  Water freezes at 0° Celsius (C) and boils at 100°C.

Water can also become a gas called water vapor.  The process of a liquid becoming a gas is called evaporation. The Sun's energy evaporates surface water. Then the water becomes water vapor in the air. You cannot see water vapor, but sometimes you can feel its effects on hot summer days. On these days water leaves your skin as sweat. But sweat cannot easily evaporate if there is a lot of water vapor in the air.  So you feel "sticky" from the sweat.

Water vapor in the air can turn back into a liquid.  This process is called condensation. When the air cools, condensation turns invisible water vapor back into drops of water. Small droplets form clouds and fog. Large drops that form on plants are dew. 

There is only a certain amount of water on Earth.  It must be used again and again.  The movement of water from Earth’s surface into the air and back again is the water cycle.  The water cycle gives us a constant supply of fresh water. 

Water changes form or state as it moves through the water cycle as it loses or gains heat energy.  The Sun’s energy and winds cause water to evaporate and become water vapor.

Water vapor rises into cooler air, cools, and turns into water droplets or ice crystals.  This process is called condensation.  These water particles collect and form clouds.

When water particles in clouds grow in size and weight, they fall faster.  Water that falls to Earth is called precipitation.  Precipitation might be rain, snow, sleet, or hail.  The type of precipitation depends on the temperature at Earth’s surface.