Floaters and Sinkers
The ability to design boats that float enhances our abilities to transport cargo, catch fish, and enjoy recreational activities.Copyright NOAA http://www.sarsat.noaa.gov/images/boats.jpg
In the first lesson, Floaters and Sinkers, students gain an intuitive understanding of density by comparing objects of equal volumes but different masses. They use different methods to determine the densities of solid objects, including water displacement to determine volumes of irregularly-shaped objects. By comparing densities of various solids to the density of water and considering the behavior of different solids when placed in water, students conclude that objects with densities greater than water usually sink while those with densities less than water float. Through the associated activity, Determining Densities, students learn to determine densities of objects and depict their results graphically (mass vs. volume). They use two different methods to determine the densities of a variety of materials and objects, some of simple geometric shapes (direct measurement of volume) and others irregularly-shaped (water displacement). Results reveal that objects with densities less than water (floaters) lie above the graph's diagonal line while those with densities greater than water (sinkers) lie below the diagonal.
Next, students complete the Clay Boats activity, which challenges them to design and build boats from modeling clay (a material that normally sinks in water) that are able to carry as much weight as possible. After discussing their observations and conclusions, students complete the Buoyant Boats activity, in which they conduct a simple experiment to see how the water level changes in a beaker when a lump of clay sinks in the water and when the same lump of clay is shaped into a bowl that floats. The surprising observation is that the floating clay displaces more water than the sinking clay. Comparing the mass of water that is displaced when the clay floats to the mass of the clay itself reveals that they are about the same. These activities prepare students to receive the content material of the second lesson, What Floats Your Boat?, giving them a full understanding of the principle of buoyancy and Archimedes' principle.
Density is a scientific property that is important in many materials engineering applications. In this unit, students experience engineering by designing boats to float with various amounts of weight.