Is it possible to measure how thick aluminum foil is by using a standard ruler? Of course not! Just imagine the looks you will get from your students when you tell them that they will need to measure the thickness of foil! This is a great activity for ninth-grade physical science students to apply their knowledge of density. This activity could be used after students have a conceptual under- standing of density but may not yet know how to apply the concept of density to solve a problem. Hila Science Videos’s (2010b) DensityandBuoyancy, found at http://hilaroad.com/video/sink float.html, explains density and buoyancy both quantitatively and conceptually.