We have just seen how the subject goes about separating out factors in order to determine their respective effects in a multi- factor experimental setup. The present chapter takes up the reactions of the child and adolescent in an analogous situation 2 with the difference that only one of the possible factors actually plays a causal role; since the others have no effect they must be excluded after they have been isolated. Such is the case for the pendulum. The variables which, on seeing the apparatus, one might think to be relevant are: the length of the string, the weight of the object fastened to the string, the height of the dropping point ( = amplitude of the oscillation), and the force of the push given by the subject. Since only the first of these factors is actually relevant, the problem is to isolate it from the other three and to exclude them. Only in this way can the subject explain and vary the frequency of oscillations and solve the problem. The pendulum problem utilizes a simple apparatus consisting of a string, which can be shortened or lengthened, and a set of varying weights. The other variables which at first might be considered relevant are the height of the release point and the force of the push given by the subject. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315009674/2bec7fb8-de4a-429e-95a4-23f710e2d74f/content/fig3_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>