What Causes Something to Sink or Float?
Ask the students to answer the following question either in their journals or on a sheet of paper. “What causes an object to sink or float in a liquid? Draw a model to think through your ideas and then write an explanation.” Circulate while students are working to make sure that they understand the question. You may wish to ask them to consider how density is a part of what happens. Some students will also include non-density related explanations such as surface tension, buoyancy, etc. Give the students about ten minutes to think about their response. Don’t have the students share their ideas just yet. RECAST Thinking Step 2: RECAST Activity: Two Candles This activity3 explores the role of density in sinking and floating and reveals the relational causality involved. Pass out the sheet, RECAST Activity: Two Candles. Do this activity as a demonstration. Do NOT foreshadow what will happen. Introduce the problem to the students by explaining that you have two beakers filled with liquid, a
