Motion, Time, and Gravity: Investigate the pendulum, periodic motion, elapsed time, and load/mass/weight. Read "What Is a Second" before discussion and introduction of the challenge. Students will investigate length, load, and materials in order to design a pendulum constant and predictable motion. Essential Question: What determines the period of a pendulum? Recommended Level: 5-8 Time: Approximately 50 minutesPurpose: Introduce the concept of periodic motion. Students discover that the period