Learners build a pendulum from a yo-yo, and then design their own experiment to determine what affects the pendulum's period of swing. They can alter the mass of the yo-yo by adding play dough, the length of the yo-yo string, or some other variable of their own choosing. Learners collect data and graph their results. This activity starts on p.17 of the manual. This manual contains 4 activities related to the Spectra's Force comic book published by the American Physical Society.