We can tell kids that floating objects displace their weight in water or we can show them with an activity like this. Here they start with a lump of clay and measure the weight of water it displaces. Next, they take that same lump and fashion it into a boat and see that not only does it float but it displaces more water than previously (and more that its weights-worth of water).
This activity gives kids practice with using gram scales. They use (and or assemble) a DIY overflow can apparatus for measuring irregular volumes. If you study Archimedes in your class, this activity would provide some great connections and discussion points.
Use this to learn and reinforce answers to questions such as:
❑ How does density compare to buoyancy?
❑ How does displacement connect to buoyancy?
❑ How can very heavy objects float?
Once students work through the activity, they can capture their observations using the included Lab Notes or probing questions included in the instructions.
Concepts Addressed
♦ Density is a measure of weight per volume.
♦ Fluids exert a buoyant force on objects that are submerged in them.
♦ Fluids push up objects whose density is lower.
♦ Gravity is a downward force while buoyancy is an upward force
Answer Keys and Teacher Notes address most questions and issues that might arise in this study—you shouldn’t have to do any outside research unless you want to.
Materials Needed Nonconsummables: Assorted plastic cups; hole punch; plastic straws; polymer clay; small objects, gram scale, scissors, old towels for cleanup.
Prep Time Collect materials (no consumables)
Teaching Time About 40 mins depending on accompanying writing assignment.
Student Sheets Scaffolded writing prompts & lab reporting
