Changes is a 16-lesson unit designed to help students investigate examples of changes that affect their daily lives. Specifically, students examine some changes that occur when solids and liquids are mixed or change state. They consider how water freezes, melts, evaporates, and condenses. They observe the properties of solids, liquids, and gases and describe some of the changes that take place when substances are combined or separated. Over the course of the unit, they notice that some changes occur quickly and that others take longer.