Piaget used a pendulum apparatus to assess whether children had reached the stage of cognitive development.

formal operational

Explanation:

The Formal operational thinking has tested experiments using the pendulum. The method involved three factors (variables) the length of the string, the weight of the object and the force or impulse that is printed on it. The task was to find out which factor is most important to determine the swing speed of the pendulum. Children who have already reached the formal operational stage solve the task systematically, testing one variable at a time.

answerscientific theory;