*52%*:**Planetary Motion***51%*:**Modular Approach to Physics: Energy and Orbits***46%*:**Modular Approach to Physics: Work and Energy in Projectile Motion***46%*:**Planetary and Satellite Motion***45%*:**Modular Approach to Physics: Projectile Motion: One Ball***45%*:**Modular Approach to Physics: Simple Harmonic Motion - Weighted Spring***44%*:**Kepler's Three Laws of Planetary Motion: An Overview for Science Teachers***42%*:**How Things Fly: Kepler's Laws of Orbital Motion***41%*:**Modular Approach to Physics: Centripetal Motion Simulator***41%*:**Modular Approach to Physics: Direction of the Acceleration in Uniform Circular Motion***38%*:**Modular Approach to Physics: Finding the Cross Product of Vectors***37%*:**Physics Suite Sample Problems: Gravitation***36%*:**Orbital Motion***36%*:**Boston University Physics Applets: Solar System Simulator***35%*:**Modular Approach to Physics: Static and Kinetic Friction***35%*:**Modular Approach to Physics: Breaking a Vector into Components***34%*:**Modular Approach to Physics: Charged Particle in Capacitor***34%*:**Boston University Physics Applets: Orbits and Periods***34%*:**Modular Approach to Physics: Fletcher's Trolley**