Children of all ages take delight in exploring objects in the world around them. Infants are intrigued by the color of a bright red block, the shape of a ball, or the softness of a teddy bear. They enjoy splashing in bath water and watching the bubbles. Through continuing explorations with everyday materials such as these, young children gain insight into the unique properties of solids and liquids.

By first grade, children are ready to go beyond making simple observations about solids and liquids and to begin to think about more challenging questions. What properties make solids and liquids unique? Are there similarities between solids and liquids? Do liquids, like solids, float and sink?

Solids and Liquids, a 16-lesson unit designed for first-graders, enables students to explore questions such as these. By observing and conducting tests with solids and liquids, students learn to identify and compare the properties of these two states of matter.

The first nine lessons provide students with the opportunity to observe, describe, and compare solids. They begin their investigations in Lessons 1 and 2 by observing color and shape, two properties with which they are already familiar. Lesson 3 allows students to explore how shape affects whether a solid will roll or stack; in Lesson 4, they determine how far solids that roll will travel down a ramp. These two lessons also introduce students to testing as a process for discovering information about certain properties of solids.

Lesson 5 challenges students to recognize that many words can be used to describe the hardness of a solid. This lesson helps students acknowledge that it is often helpful to describe the hardness of a solid in reference to another solid. For example, to say simply that a solid is "hard" is less informative than to say it is "harder than a rubber ball."

Testing continues in Lesson 6, where students place a set of solids in water and make new discoveries about floating and sinking. In Lesson 7, students test a set of solids to find out which ones are attracted to a magnet.

Lesson 8 provides an opportunity for students to apply the observations they have made about the properties of solids. Each student sorts a set of solids into groups on the basis of a property of his or her choice. Applying what he or she has learned, the student's partner then tries to guess why the solids have been grouped in that particular way. The lesson also enables students to demonstrate ways of sorting the solids that they have not investigated in class.

Lesson 9 is an embedded assessment that challenges students to apply what they have learned in the first eight lessons of the unit. Students observe and compare two new solids and conduct tests to learn still more about their properties. This activity enables you to evaluate the students' ability to describe the solids on the basis of the properties they have examined in class and to evaluate the way students use tests to learn more about the solids.

Students begin their investigations of liquids in Lesson 10 by exploring the look and feel of two liquids. During Lesson 11, students examine a drop of four liquids under a hand lens and discover that the drops are of varying sizes. Further examinations reveal that liquids flow on waxed paper in different ways. In Lesson 12, students discover a property shared by all liquids, namely, they have no definite shape.

In the next lessons, students perform a series of tests to learn more about the properties of the liquids. In Lesson 13, they conduct "drop races" as a way to investigate how the viscosity or fluidity of a liquid affects the speed at which it moves down a slick surface. Students share their observations of which drops "win" the races and compare them with their earlier observations of the ways liquids flow.

In Lesson 14, students observe what happens when they add other liquids to water. They observe that some liquids float and others sink; some liquids mix after they are stirred and others remain separate. These observations introduce another property of liquids--whether or not they are miscible with water. In Lesson 15, students examine two new liquids. These investigations allow you to assess students' ability to describe the liquids on the basis of the properties they have investigated as well as to evaluate how they use tests to learn more about the liquids.

Finally, in Lesson 16, students compare the similarities and differences between solids and liquids and summarize their observations of the properties of solids and liquids in a Venn diagram. This embedded assessment allows you to evaluate the growth in students' knowledge of the properties of solids and liquids.

Following Lesson 16 is a post-unit assessment that is matched to the pre-unit assessments in Lessons 1 (focuses on solids) and 10 (focuses on liquids). The additional assessments provide further questions and challenges for evaluating student progess.