Lesson Summary Students solve a new problem by applying their knowledge about how the weight, size, and design of an object as well as the liquid in which the object is placed, affect its buoyancy. Students weigh mystery cylinders with a spring scale. They predict and test the floating behavior of mystery cylinders in fresh and salt water. They compare the mystery cylinders to objects they have tested in previous lessons. Teacher Background One could use this lesson as a summative or embedded assessment. The mystery cylinders are made of acetyl delrin. Acetyl delrin is a type of plastic that is used to make handles of kitchen knives, as well as other things. This activity gives students the opportunity to make direct comparisons between the mystery cylinders and the objects they have already worked with.  The class weight graph, created in previous lessons, is a valuable resource tool in this investigation. Encourage students to place particular emphasis on explaining their reasons for their predictions. Set-up/Management Tips Set up tanks of 2 liters fresh and 2 liters salt water for each group. Make sure the tanks are clearly labeled. Separate the cylinders from the object bag for student use. The water-filled cylinder, with masking tape handle, is used in this investigation Literacy Support Scientific Vocabulary The following words are key vocabulary words that will be introduced in this lesson and reinforced throughout the unit: Mystery Cylinders