Floaters and Sinkers: Curricular Unit

Abstract:: This curricular unit introduces students to the important concept of density. The focus is on the more easily understood densities of solids, but students can also explore the densities of liquids and gases. Students devise methods to determine the densities of solid objects, including the method of water displacement to determine volumes of irregularly-shaped objects. By comparing densities of various solids to the density of water, and by considering the behavior of different solids when placed in water, students conclude that ordinarily, objects with densities greater than water will sink, while those with densities less than water will float. Students then explore the principle of buoyancy, and through further experimentation arrive at Archimedes' principle, which states that a floating object displaces a mass of water equal to its own mass. They may also be surprised to discover that a floating object displaces more water than a sinking object of the same volume.

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How a Faucet Works

Abstract:: Students learn about the underlying engineering principals in the inner workings of a simple household object -- the faucet. Students use the basic concepts of simple machines, force and fluid flow to describe the path of water through a simple faucet. Lastly, they translate this knowledge into thinking about how different designs of faucets also use these same concepts.

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Abstract:: Students use modeling clay, a material that is denser than water and thus ordinarily sinks in water, to discover the principle of buoyancy. They begin by designing and building boats out of clay that will float in water, and then refine their designs so that their boats will carry as great a load (metal washers) as possible. Building a clay boat to hold as much weight as possible is an engineering design problem. Next, they compare amount of water displaced by a lump of clay that sinks to the amount of water displaced by the same lump of clay when it is shaped so as to float. Determining the masses of the displaced water allows them to arrive at Archimedes' principle, whereby the mass of the displaced water equals the mass of the floating clay boat.