Teaching Physics with the Physics Suite

Edward F. Redish

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Floating and sinking

Suppose you have the following collection of objects:

Which of these objects do you expect will float and which will sink on water? Will it make a difference if you carefully place the object with its largest surface on the surface of the water? In which cases? Discuss the criteria you come up with, explaining carefully why you decided on each one and why it plays a role. After you have written your answer, perform the experiments and compare your results with your predictions.

Note to the instructor: Floating and sinking is much more non-intuitive than one might guess at first. The process is, in real-world experience, a quite complex balance between buoyancy, gravity, and surface tension, with battleships that float and wood (some special types) that sink. Students often have problems with the concept of density [Arons 1990]. This kind of activity can help them think about what we know and how we know it.

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Page last modified October 30, 2002: M12