Teaching Physics with the Physics Suite

Edward F. Redish

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Bobbing boats

A long straight jetty that is used to keep a calm, wave-free harbor available for boats has had two holes broken into it by a storm. A series of long wavefronts parallel to the jetty strike it giving rise to outgoing circular waves through the holes. A set of such waves is shown at a particular instant of time in the figure below.

A fisherman watching various boats for a while after this picture was taken notices that some of the boats oscillate up and down a lot as the waves pass them and some oscillate almost not at all. The boats are labeled A, B, C, and D. (Take their positions as being at the center of their indicating letters.)

Rank order these boats starting with the one that has the largest amplitude of oscillation to one that has the smallest. If any two are nearly equal, indicate that. Thus, your answer might look like W > X > Y = Z to indicate that W had the largest oscillation, and Y and Z had the smallest oscillation and they were equal. If you expect a boat not to oscillate at all, indicate by writing, for example, Z = 0. Explain your reasoning.

Page last modified April 9, 2009: OP39