Become an engineer, and design a submarine that moves in the water like a real submarine. Try making it sink, float, and hover in the water.

For a dramatic illustration of density check out this demonstration. It's simple to do, only requiring a bowling ball and some water.

Learn about density in this hands-on science experiment. Includes full list of materials, procedures, and scientific explanation of what makes an object float or sink. [PDF]

Try this at-home science experiment to learn if salt affects the way things float.