Isaac Newton was born on December 25, 1642 in Lincolnshire, England. His father had died two months before his birth. When he was three, Newton’s mother got remarried, and he stayed with his grandmother. He was not interested in the family farm, so he was sent to Cambridge University to study. Isaac Newton explained the workings of the universe through mathematics. He formulated laws of motion and gravitation. These laws are math formulas that explain how objects move when a force acts on them. Isaac Newton used three laws to explain the way objects move. They are often called Newton’s Laws. The first law states that an object at rest will remain at rest unless acted upon by a nonzero force. An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by a nonzero force. In other words, an object that is not being pushed or pulled by some force will stay still, or will keep moving in the same direction at a steady speed. The tendency of an object to remain still, or keep moving in one direction at a steady speed is called inertia. The second law explains that an object’s acceleration depends on its mass and on the net force acting on it. Basically, it explains how a force acts on an object. An object accelerates in the direction the force is moving it. The third law states that if an object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. In other words, if an object is pushed or pulled, it will push or pull equally in the opposite direction. When most people think of Isaac Newton, they think of him sitting under an apple tree, observing an apple fall to the ground. When he saw the apple fall, Newton began to think about gravity. Newton understood that gravity was the force of attraction between two objects. He also understood that an object with more mass exerted the greater force, or pulled smaller object toward it. That meant that the large mass of the earth pulled objects toward it. That is why the apple fell down instead of up.
Isaac Newton thought about gravity and the apple. He thought that maybe gravity was not just limited to the earth and the objects on it. Newton also thought that gravity extended to the moon and beyond. He calculated the force needed to keep the moon moving around the earth. Then Newton compared it with the force that made the apple fall downward. After allowing for the fact that the moon is much farther from the earth, and has a much greater mass, he discovered that the forces were the same. The moon in held in an orbit around earth by the pull of earth’s gravity because the earth has a greater mass.
Isaac Newton’s calculations changed the way people understood the universe. No one had been able to explain why the planets stayed in their orbits. What held them up? Less than 50 years before Isaac Newton was born it was thought that the planets were held in place by an invisible shield. Isaac proved that they were held in place by the sun’s gravity. He also showed that the force of gravity was affected by distance and by mass. He was not the first to understand that the orbit of a planet was not circular, but more elongated, like an oval. What he did was to explain how it worked.