This science video explains the relationship between buoyancy and density using hot air balloons, fish and cruise ships as examples of objects using buoyant force. This video tutorial also includes instructions for calculating the density of a rectangular prism and a liquid. If you like science experiments, you can't miss this one.
You'll also get a brief explanation of Archimedes' Principle and the role gravity plays in buoyant force. It supports the teaching of these concepts in junior and middle school.