Biography: Sir Isaac Newton

Isaac Newton was born in 1642 in a manor house in Lincolnshire, England. His father had died two months before his birth. When Newton was three his mother remarried and he remained with his grandmother. He was not interested in the family farm so he was sent to Cambridge University to study.

Isaac was born just a short time after the death of Galileo, one of the greatest scientists of all time. Galileo had proved that the planets revolve around the sun, not the earth as people thought at the time. Isaac Newton was very interested in the discoveries of Galileo and others. Isaac thought the universe worked like a machine and that a few simple laws governed it. Like Galileo, he realized that mathematics was the way to explain and prove those laws.

He formulated laws of motion and gravitation. These laws are math formulas that explain how objects move when a force acts on them. Isaac published his most famous book, Principia in 1687 while he was a mathematics professor at Trinity College in Cambridge. In the Principia, Isaac explained three basic laws that govern the way objects move. He also described his theory of gravity, the force that causes things to fall down. Newton then used his laws to show that the planets revolve around the suns in orbits that are oval, not round.

The three laws are often called Newton’s Laws. The first law states that an object that is not being pushed or pulled by some force will stay still or will keep moving in a straight line at a steady speed. For example, if someone is riding a bike and jumps off before the bike is stopped what happens? The bike continues on until it falls over. The tendency of an object to remain still or keep moving in a straight line at a steady speed is called inertia.

The Second Law explains how a force acts on an object. An object accelerates in the direction the force is moving it. If someone gets on a bike and pushes the pedals forward the bike will begin to move. If someone gives the bike a push from behind, the bike will speed up. If the rider pushes back on the pedals the bike will slow down. If the rider turns the handlebars, the bike will change direction.

The Third Law states that if an object is pushed or pulled, it will push or pull equally in the opposite direction. If someone lifts a heavy box, they use force to push it up. The box is heavy because it is producing an equal force downward on the lifter’s arms. The weight is transferred through the lifter’s legs to the floor. The floor also presses upward with an equal force. If the floor pushed back with less force, the person lifting the box would fall through the floor. If it pushed back with more force the lifter would fly up toward the air.

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 a specific kind of motion called gravity. Newton understood that gravity was a force of attraction between two objects. He also understood that an object with more matter or mass exerted the greater force, or pulled smaller objects 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 and why people don’t float in the air.

He also thought that maybe gravity was not just limited to the earth and the objects on the earth. What if gravity extended to the moon and beyond? Newton calculated the force needed to keep the moon moving around the earth. Then he 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 and that the moon is also held in orbit around earth by the pull of earth’s gravity.

Newton’s calculations changed the way people understood the universe. Prior to Newton, no one had been able to explain why the planets stayed in their orbits. What held them in place? People had 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 and that the force of gravity was affected by distance and by mass. While he was not the first to understand that the orbit of a planet was elongated like an oval, he was the first to explain how it worked.