Most of you, no doubt, know the story of Newton and the falling apple and how it led to his discovery of the law of gravity. But how much do you know beyond that? Do you know what kind of man this great scientist was? or where he stands in the history of science? If you don't, or even if you do, read the following lesson.
Isaac Newton was born on Christmas Day, 1642. He grew up in the English countryside. From the very first Newton was very much interested in the mysteries of nature. One of the most difficult scientific problems of Newton's day was about the question of motion. Why did objects move? Scientists could see that stones rolled down hills, that wind blew leaves along the ground, and heavy objects fell to the earth when dropped.
After Copernicus, they began to admit that the earth itself moved. "Were there laws that govern these various kinds of motion?" they asked themselves. The Greeks had believed there were different rules for motion on earth and in space, and that there were unnatural movements on the surface of the earth.
Galileo was the first person to challenge this Greek view of motion. This Italian scientist was a follower of Copernicus. It didn't make much sense to Galileo to have different rules for motion on earth and in space. He made two important discoveries. First, he showed that motion was not unnatural. On the contrary, an object once in motion would tend to continue in motion. Second, Galileo worked out a mathematical formula for the motion of all objects that fell to the earth.
Galileo, however, did not explain how all motion in the universe worked. Much work had been done since Copernicus to observe and record the movements in the solar system. It remained now for some great mathematical mind to pull this work all together and put it into universal laws.
At the age of twenty-three Isaac Newton moved from Cambridge to his country home. There his thoughts turned to the problems of motion. As Newton himself later told the story, he was sitting in the garden one evening, thinking, when he noticed a falling apple. The apple set him to wondering about the movement of falling things.
It occurred to him that the force which caused fruit to fall from trees worked quite as well at greater distances from the center of the earth -- on top of buildings or even on top of mountains. Perhaps, thought Newton, this same force reached out much farther still, even to the moon. Was it this force which kept the moon going around the earth? And if so, could not the same force explain the movements of the planets around the sun? Newton began to search for a mathematical expression of his idea.
In 1669 Newton became professor of mathematics at Cambridge. Three years later he joined the Royal Society. The Royal Society was a group of learned men from all branches of science. Before long Newton began again to study the problems of motion. He had already discovered the essential ideas, but it still remained for him to solve the difficult mathematical problems. At last he seemed to have solved the main difficulties. But he did not publish his findings at once.
Only in 1687 did he at last publish his new theory. Newton's great work, The Mathematical Principles of Natural Philosophy, marked the triumph of the Scientific Revolution. The very title is significant. Newton had found the mathematical principles, the scientific laws which governed the movements of earth and heavens. The book completed the working out of a new view of nature, a task begun by Copernicus.
The result was an exact mathematical world. Newton put forward three laws of motion in the book.
The first law stated that bodies will tend to move in a straight line with uniform motion unless acted upon by a force. Thus, a bullet shot from a gun moves straight ahead until it is stopped by a target or it slows and falls as a result of the friction caused by moving through air.
The second law stated that the force applied to a body is in proportion to the acceleration of the body. Thus, the harder you throw a ball the faster it will move.
The third law said that every action has an equal and opposite reaction. Thus, when you hit a punching bag, it bounces right back at you.
Newton also worked out a mathematical expression for gravity. It applied equally to the apple falling from the tree and the moon going around the earth. Newton was soon recognized as the leader of English science. In 1703 he became president of the Royal Society.
Science was never quite the same after Newton's discoveries. Little wonder that the eighteenth-century poet Pope, looking back at Newton's work, wrote: "Nature and Nature's laws lay hid in night; God said, Let Newton be! -- And all was light."
Newton, however, never rested on his fame. He continued to work and study. In his last years he once said to a friend, "I do not know what I may appear to the world, but to myself I seem to have been only like a boy, playing on the seashore, and now and then finding a smooth pebble of a pretty shell, while the great ocean of truth lay undiscovered before me."