Newton

On Christmas day 1642, the year Galileo died, Isaac Newton (1642-1727) was born in a Lincolnshire farmhouse. He was born prematurely and was so tiny that he was not expected to live. Newton’s father was an illiterate yeoman farmer who died three months before Isaac was born. Newton went to school in the local day schools and later in Grantham, but was more interested in building mechanical devices than in studying. His mother married a local vicar and went to live with him when Newton was four years old, so his grandmother cared for him. Newton left school at age 14 when his stepfather died because he had to go help his mother on the farm, but was so absent minded and absorbed in books that he was sent back to school at the persuasion of his schoolmaster. In 1661, Newton entered Trinity College, Cambridge University. He graduated in 1665, at age 23, without making any particular distinction for himself. That year, bubonic plague broke out in England and Newton went to Woolsthorpe, the location of his mother’s farm, to avoid it. While sitting in an orchard one warm afternoon, he saw an apple fall to the ground and started to wonder about gravity. He wondered why apples always fell toward the center of the earth. He reasoned that all matter must attract all other matter. The theory of gravity was not an original idea, but Newton was the first to recognize that it could extend into infinity. He also experimented with the nature of light by using a prism. He returned to Cambridge in 1667 and became a professor of mathematics there in 1669, lecturing once a week on subjects such as arithmetic, geometry, astronomy, and optics. In 1672, he was elected into the Royal Society, an organization founded in 1660 to promote the natural sciences. That year, he also constructed the first reflecting telescope and invented calculus.

Newton published two books, Principia in 1684, and Opticks in 1704. At first, Newton did not plan to publish his first book, but at the persuasion of Edmond Halley, who corrected his proofs for the law of gravity and paid all of the expenses, he did. Newton did not enjoy the arguments that arose from his discoveries. Principia includes the first unified theory that explains what happens in space, which includes Newton’s laws of motion and gravitation. Some consider it to be one of the greatest contributions to science. Newton published Opticks twenty years later in which he writes about his discoveries with light. He explains how people see objects as colored and tells about his discovery that sunlight is a combination of all colors. He said that an object is a certain color because the object absorbs all other colors in the spectrum except that particular color. His work laid the foundation for the science of spectral analysis.

Newton became warden of the mint in 1696 and in 1699 became master of the mint where he helped reform the coinage system. He was knighted in 1705 by Queen Anne. He never married and spent much of his time studying subjects such as alchemy, theology, and the chronology of ancient civilizations. He was very sensitive to criticism and had to be pleaded with to publish his most valuable work. He died in 1727 and was buried in Westminster Abbey. Shortly before he died, he said of himself, “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 diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.” Newton said of himself at another time, “If I have seen further than other men, it is because I have stood upon the shoulders of giants.”

Newton's Laws

First Law of Motion: Every body continues in a state of rest or of uniform motion in a straight line unless acted upon by an external force. This law was originally formulated by Galileo.

Second Law of Motion: If a force is applied to a body, the rate of change in the body’s linear momentum is proportional to the applied force and occurs in the same direction as the applied force. This can be expressed in the following equation: F = ma, where F is the applied force, m is the mass of the body, and a is the resulting acceleration of the body. In other words, force equals mass times acceleration. Einstein modified this law.

Third Law of Motion: For every action, there is an equal and opposite reaction.

Newton’s Law of Universal Gravitation: The force of attraction between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. This is illustrated in the following equation.

G is the constant of gravitation. It was found to be .0000000667 cm per gram second squared.
M is the mass of the first or second body, depending on the subscript used (1 or 2).
F is the force of attraction between the bodies.
D is the distance between the bodies.

Newton’s Law of Cooling: The rate of cooling is proportional to the difference in temperature between the object and its surroundings. This means that if the difference in temperature is great, the change in temperature will be fast, if the difference is small, the change in temperature will be slow. This is a type of exponential decay, which is described in a logarithmic equation. This means that, although the temperature of a body will get closer and closer to that of its surroundings, the two temperatures will never be equal.

Newton’s Modification of Kepler’s Third Law:

Newton modified Kepler’s third law using his laws which resulted in the following equation:

The subscript means the sun.
The subscript p means planet.
M is the mass of the sun or planet, depending on which subscript is used.
G is the constant of gravitation. It was found to be .0000000667 cm per gram second squared.
A is the planet’s average distance from the sun. (Semimajor axis)
P is the planet’s orbital period.

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