Thursday, January 07, 2010

Isaac Newton

Sidebar: Newton

Centuries ago in merry old England, Isaac Newton was a young student at Cambridge. These were considered his "golden years" because he was young, full of energy, and motivated, and he put all this youthful enthusiasm into study. Isaac's Cambridge studies were interupted by the Black Plague and forced Newton to take a lengthy break at his home farm. Legend has it that he was sitting under an apple tree and observed an apple falling by itself from a branch to the ground.

"Something made that apple move from the end of a tree branch to the ground; what was it?", he thought to himself. Being a genius, Newton eventually deduced a force that "acts at a distance" throughout the universe. This is best described by Newton's universal constant of attraction (gravitation) which applies between any two bodies of mass. There are literally libraries full of books about the phenomena of gravity, but we care most about the following aspect: Earth's surface gravity attracts objects at a force that tends to accelerate them at 9.8 meters per sec per sec. It turns out that gravity and acceleration are closely intertwined.

Isaac Newton wrote that he might see further then others because he was "blessed to stand on the shoulders of giants". He wrote this phrase in a letter to the Royal Academy and was implying his two colleagues, Robert Hooke and Edmond Halley. Of course, both Hooke and Halley were well known scientists both then and throughout history, but they were nowhere near the stature of Newton. In modern times, many people now take Newton's famous analogy to mean the two emminent historical figures, Johannes Kepler and Galileo Galilei.

Another interesting item: Newton is reputed to be born on Christmas Day of the same year (1642) that Galileo died.

Of Newton's many discoveries, perhaps the most reknown is the concept that an object continues to travel at a constant velocity until a force changes either its direction or speed. Given that concept, it's an easy leap to conclude that a force causes mass to accelerate, or force is the result of mass accelerating (F = ma).

Universal constant of gravity, G, describes "force at a distance". Force makes objects accelerate (change velocity); conversely, acceleration gives objects a force. Thus, gravity (force at a distance) causes objects to accelerate; thus, this same acceleration can produce same force as gravity.

Paraphrasing text from "The Life of Isaac Newton" by R.S. Westfall.

In 1684, Dr. Halley came to visit Sir Isaac at Cambridge. After some conversation, Dr. Halley asked what Sir Isaac thought the curve would best describe path of the planets given the force of attraction towards te Sun to be reciprocal to the square of the distance from it (inverse square).

Sir Isaac immediately replied that it would be an ellipse.

Dr. Halley: "How did you come to that conclusion?"

Sir Isaac: I calculated it.

Dr. Halley asked for that calculation. Sir Isaac looked for the paper and could not find it right away; however, he later rewrote it as "On the Motion of Bodies in an Orbit". This became the impetus for Sir Isaac's masterwork, "The Principia"; and Halley is now famous for many things, most notably the comet that bears his name, but most importantly for ensuring that Newton eventually produced that work. Among many other key players involved in producing the Principia are included: Edward Paget and Humphry Newton (no relation).

Suggested Outline for relevant Newton research:



-momentum exchange


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