Clay Boats

Density is an important property in many materials engineering applications. Building clay boats to hold as much weight as possible is a classic engineering design problem.

After this activity, students will be able to:

• Describe a means to make a material that is denser than water (modeling clay) float.
• Describe the steps of the engineering design process used to create a dense but floatable object.

Very little introduction is required for this fun activity. In fact, this activity makes a good introduction for the associated lesson. However, if students did not already complete the Determining Densities activity portion of the Floaters and Sinkers lesson, introduce this activity by showing the class a half-stick of modeling clay and asking if they think it will float or sink in a beaker of water.

After students make their predictions, drop the clay stick into a beaker of water to demonstrate that the clay sinks. Then write on the board, "Engineering desgn challenge 1: Create an object out of clay that floats." (Then continue with the activity, as described in the Procedures section.)

With the Students: Challenge 1 (5-10 minutes)

1. Have each student tape a sheet of waxed paper (~18" long) on the surface of his or her work station. This makes cleanup much easier, since wet clay gets very messy.
2. If you have not already done so, write on the board, "Engineering design challenge 1: Create an object out of clay that floats." Note that the wording specifies the creation of an object as opposed to a boat. In fact, students who attempt to mold their clay into the shapes of familiar boat hulls will quickly realize that these shapes are less than ideal – at least for clay.
3. Give each student a half stick of modeling clay, and place several tubs of water throughout the classroom. Let students know they can test their objects as often as they like, but advise them to pat the clay dry after testing and before shaping it into a new design.

With the Students: Challenge 2 (15-20 minutes)

1. As students successfully complete Part 1, challenge them with a new goal. Write on the board, "Engineering design challenge 2: Design an object out of clay that can carry the largest load of washers possible." Show students the washers that will be used to make up the load.
2. As students work, encourage them to continue making improvements every time their boats sink. Students may become competitive and want to declare a winner, and it is quite possible that a tie for the number of washers supported will occur. Should this happen, use a balance to determine the actual mass of the washers held, since slight variations exist in the masses of individual washers.

Design Process Reflection: Ask students to each write a paragraph describing in their own words the steps of the engineering design process that they followed as they created something new and unique—a clay object that floats in water.

Making Sense: Have students reflect on the science concepts they explored and/or the science and engineering skills they used by completing the Making Sense Assessment (PDF).

If students do not dry their clay adequately between tests of "seaworthiness," the clay may become too wet to work with. Have some extra clay on hand to give to students if their original portions becomes unworkable.

Expect students to have a number of observations about the shapes of successful boats, and express some curiosity about "real" boats and their design features. Assign students conduct library and Internet research to find out about boat designs and how they affect performance. Information on this subject is also covered in the Lesson Background & Concepts for Teachers section of the associated lesson.