Lesson 2 Gravity and the Solar System: We learned that gravity is a force of attraction between all objects in the universe due to their masses. Then we learned about Kepler’s three laws of planetary motion: planetary orbits are elliptical, planets move faster in their orbits when closer to the sun, and the distance of a planet from the sun to the time it takes to go once around its orbit. Next we learned about Newton’s law of universal gravitation and the formation of the solar system.