Maybe you have heard the story of what prompted Isaac Newton to think of the concept of gravity—he was sitting under a tree when an apple fell on his head. Upon the fall, he brilliantly came up with the theory of gravity. Though the story is likely embellished, but the fact remains, Newton was inspired by at least the thought experiment of the falling apple. Through his studies, he came up with the concepts of universal gravitation that have helped scientists understand this thing called gravity.

Everyone is familiar with gravity, even if they cannot explain the scientific concepts or the mathematics behind it. You have already studied and used it in calculations of free fall and other situations, but you have also experienced it every day of your life. From the ability to stay fixed to the ground and the knowledge that if you dump over your drink, your understanding of gravity extends beyond the theory and into practice. The force of gravity causes things to accelerate towards the center of the Earth. If you jump up, the pull of gravity slows you down on the way up and speeds you up on the way down. You've been referring to this force as the force of gravity and using the acceleration of g = -9.81 m/s² on Earth.

So far, your studies have been centered around what happens her on the surface of the Earth. In this lesson, you will explore how gravity effects things from a much larger, universal perspective. You will be introduced to Kepler's Laws of Planetary Motion as well as Newton's Universal Law of Gravitation.