1) example of positive feedback loop: nuclear fission, with self-sustaining nuclear chain reaction caused by emission of neutrons.
example of negative feedback loop: Potential and Kinetic energy of pendulum. As one increases, the other decreases.
2) nuclear fisison: game of tag starting with one person (the fox) tagging everyone else (the hares). Rule: when tagged, you become a fox. Number of foxes will increases exponentially
PE vs KE: use online simulation of skatepark. Have students compare PE and KE and the sum of both.