Isaac Newton (1643-1727) was an English mathematician and physicist. He presented his physical findings in his Magnus opus, Philosophiae Naturalis Principia Mathematica (1687). In that book he described the laws of gravitation and the three laws of motion.
Newton’s finding constituted that part of physics called mechanics and lasted until the twentieth century when Albert Einstein’s special and general relativity finally improved on it.
Newton showed that the motions of objects on earth and elsewhere in the universe are governed by the same gravitational laws. He re-confirmed that the heliocentric view of our solar system is correct and laid to rest the questions posed by Galileo’s recanting of his heliocentric finding.
Newton’s mechanics explicated the laws of conservation of momentum and angular momentum.
Newton, along with Leibniz, invented Calculus. He also made useful contributions to optics and improved on the telescope.
In optics Newton described light as composed of corpuscles (what we now call particles or photons) and that light moves to darker medium.
Newton recognized that light must behave as waves; he had to make that assumption (he did not actually demonstrate the wave theory of light) for him to explain refraction of light.
Given his recognition that light behaves both as particles and waves (both propositions proved in the early twentieth century) it can be argued that Newton laid the ground work for today’s special relativity and quantum mechanics. However, physicists after him did not pursue the idea that light is in particles but, instead, only embraced the wave function of light.
Newton’s fame rested on his mechanics (the gravitation and its effects on planetary orbiting) and the laws of motion.
Newton’s first law of motion (law of inertia) states that an object at rest tends to remain at rest and that an object in motion tends to remain in motion unless acted upon by another object.
Newton’s second law of motion is that an applied force (f) on an object equals the time rate of change of its momentum (P) The acceleration of an object is directly proportional to the magnitude of the force acting on it, and inversely proportional to its mass (F=ma).
Newton’s third law of motion states that for every action there is an equal and opposite action.
There is a whole lot of mythology on how Newton derived his principles of gravitation and motion. Some claim that he had seen an apple fall from a tree to the ground and wondered why the apple did not fall up and from that observation surmised that a force (gravity) was pulling the apple downwards instead of upwards.
There is little or no evidence that this apple falling incident occurred; nevertheless, it is useful in thinking about gravitation.
Why do things fall down instead of up? What force pulls things to the ground? Gravite is Latin for weight. A force that pulls something to itself must have more weight (mass) than what it attracts to it. The earth, ground, must have more weight (mass) than the apple that it pulls towards it.
Extrapolating from this phenomenon one then asks: why do objects in space that have more weight not pull smaller objects towards them and have them crash into them. Since the earth has less mass than the sun, why does the earth not crash into the sun? Something must keep both the sun and the earth (and other objects in space) in their orbits. What is that? Newton really did not answer this question. Albert Einstein’s special relativity and its demonstration of the curving of space-time around objects did, hence improved Newton’s mechanics.
Newton worked out how objects move (motion) and how once an object is in motion it requires another force of greater weight to dislodge it from its trajectory.
Newton’s mechanics dominated the study of science and applied science, that is, engineering, until the early twentieth century’s special relativity and quantum mechanics improved on it.
Newton’s fame was far and wide. Naturally, his fame attracted admirers. It is said that Newton formed a relationship with a Swiss mathematician, Nicolas Fatio de Dullier. It is reported that the two men may have had a homosexual relationship, for when the relationship broke up Newton went into deep depression from which he scarcely recovered. Considering his awkwardness in society, he had poor social skills causing some to speculate that he may have had an aspect of autism called Asperger’s syndrome, it is easy to see how he could have formed a romantic relationship with a man who gave him attention. Newton never married and this adds to the conjecture that he was gay. (The gay community, in its efforts to claim most of the important men of history as one of their own, cites him as a homosexual man.)
However, in light of Newton’s religious beliefs, it is difficult to see him as a homosexual. He appeared to have taken the bible rather seriously. A literalist interpretation of the Bible certainly shows that the Christian God forbids homosexual acts.
One of Newton’s religious views is that:
“Gravity explains the motions of the planets, but cannot explain who set the planets in motion. God governs all things and knows all that is or can be done.”
Newton wrote rather extensively on religious matters but we are not here interested in religious matters; we are interested in Newton the physicist.
Newton was an alchemist; he experimented on how to transform base metals into gold.
Newton engaged in occult studies.
We are only interested in Newton’s mechanics, his laws of motion. The interested reader can explore the many dimensions of Newton’s life by reading up on his other interests.
In sum, Newton contributed more to science than any man who had lived before him. For three hundred years after him, science essentially meant Newton’s science. It was only in the twentieth century that Newton’s mechanics was improved on by Einstein’s special relativity and by quantum mechanics. Newton’s contribution to science is immeasurable.
Isaac Newton. Philosophiae Naturalis Principia Mathematica. (1687)
Isaac Newton. Opticks. (1704)