  We report on our study of student understanding of the physics of mechanical
waves, specifically the propagation and superposition of simple wavepulses
traveling on long, taut strings. We introduce the terms "particle pulses mental
model" to describe the reasoning approach that students use to guide their
thinking in wave propagation and superposition. Student responses on free
response and multiple-choice, multiple response questions dealing with the same
physics show inconsistent student thinking, where they may have both correct
and incorrect ideas about the concepts.
