Abstract: A simulated primary movement system was designed in this experiment. 14children aged from 5 to 10 were asked to compare the bus speed in thesystem. Analysis of the protocol of the subjects' performance showed: (1)there were two kinds of errors in their problem solving error in knowle-dge and errors in strategy; (2) In their problem solving, it was found thatthey used four different strategies, which reflected to a certain extentchildren's cognitive development level. On the basis of these results, theauthors discussed the role of knowledge and strategy in problem solvingand the relationship between them.

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