ABSTRACT
In this experiment the subject is presented with five disks graduated in size and rigidly affixed to a single horizontal axle. The smallest disk has a radius of 2 cm; each of the others is 2 cm greater in diameter than the preceding. All have a small plug at the same point on their circumference to which 1 of 5 weights may be attached so that it hangs to one side or the other along the circumference of the disk (see Fig. 11.1). The weights vary from 50 g to 250 g and have strings so they can be suspended from the disks. The problem is to conserve the equilibrium of the system by attaching weights to at least two different disks, one weight per disk, as the subject wishes. The law that the child must find is that the sum of the products of the weights and the radii of the disks must be the same in both directions. Situations are represented in the following way: 1↙2 ↙ 2 ↙5 = 3↘4, where 1, 2, and 3 designate disks; 2, 5, and 4 designate weights; and the arrows designate the direction of rotation. The moment to the left (↙) would therefore be (1 × 2) + (2 × 5) and the moment to the right (↘) would be 3 × 4. Coaxial disk apparatus. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203771600/cdd8d45c-f71f-401b-b13f-75887a16c5b9/content/fig11_1_C.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>
