Aristarchus is important but I Meant to say Eratosthenes as number 4
Eratosthenes- looked down a well in Alexandria one day and noticed the sun was directly over head as the bottom was clearly showing itself with no shadow- I believe it was also the summer solstice. On another year he measured the angle of the shadow on a stick in syene- so he had the critical angle of the shadow cast by the sun. Others might have thought it was a good day to clean the well but he decided to have his friend pace off the distance between syene and Alexandria
Using geometry and this dudes accurate pacing off distance and that angle he came very close to the todays estimated diameter of the earth in a day with out technological measuring devices.====
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Eratosthenes
276-195 B.C.E.
It can be said that Eratosthenes is most widely known as a famous Greek mathematician. What most people probably do not know is that Eratosthenes is not only a famous mathematician but also a well known geographer, astronomer and historian.
Before I get into a few of his accomplishments, let me tell you a little about his personal history. Eratosthenes was born in Cyrene, Greece, which is now known as Libya, in North Africa, in 276 B.C.E.. It is believed that he starved himself to death in 195 B.C.E. due to the fact that he became blind and could no longer work. As a young man, Eratosthenes studied in Athens. Eventually, he made such a name for himself in his many fields that he caught the attention of the ruler of Egypt, Ptolemy III. Ptolemy III invited Eratosthenes to Alexandria, Egypt for two reasons; to tutor his son and to be the librarian for the great Alexandrian University. Eratosthenes jumped at the chance. At the University, he was able to at most interested him and associate with other scholars. Now on to his accomplishments. . .
One of his major accomplishments in mathematics is his creation of a sieve that determines prime numbers up to any given limit. This sieve, which is called, the Sieve of Eratosthenes, is still important today in number research theory. Prime numbers are natural numbers greater than 1 that can be divided without remainder only by itself and by 1. Eratosthenes figured out that if you were to write down all the natural numbers from 2 to infinity and "sieve out" every second number after two (or multiples of two), then move to the next available number (3) and continue to "sieve out" every multiple of 3 and so on, one would end up with a list of prime numbers.
Eratosthenes is also known for his achievement in astronomy. Several astronomers and mathematicians before and after Eratosthenes tried to accurately measure the circumference of the Earth, but is was Eratosthenes that came through. He found the circumference of the Earth to be nearly 250,000 stadia (25,000 miles). Eratosthenes observed that the sun shone directly down a well at high noon on the day of the summer solstice in Syene and that it cast a shadow in Alexandria, directly south of where the well was. To calculate the circumference of the Earth, Eratosthenes measured the angle of the shadow to the Earth. Until he realized this, Eratosthenes believed that the sun was so far away that its rays were parallel. It is also believed that Eratosthenes made a star catalog with approximately 675 stars and created a calendar that included leap years.
As a historian, Eratosthenes decided to work on giving a systematic chronography of the known world by figuring out the dates of literary and political events from the siege of Troy up until his time. However, this was only a beginning. Others built on his foundation.
There is still more. Eratosthenes also contributed to geographic source of the river. Many scholars that preceded Eratosthenes in the study of the Nile river, tried to figure out the reason why parts of the river flooded while other parts did not. It was not until Eratosthenes that a correct answer was proposed. He believed that heavy rains near the source of the Nile was the cause of Many of Eratosthenes' peers nicknamed him "Beta" which is the second letter of the Greek alphabet, indicating that he just fell short of first place. Eratosthenes contributed greatly to many different areas of knowledge, more than I could cover in this short paper. Maybe in his time period, his peers did not feel that he contributed enough in one area or maybe they were jealous that he had contributed so much to so many areas. For a man who was nicknamed Beta, it is pretty impressive that so much of his work in these areas is still discussed today, so many years later.
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Gravity is More Than a Name
The Apple, the Moon, and the Inverse Square Law
Newton's Law of Universal Gravitation
Cavendish and the Value of G
The Value of g
Nearly every child knows of the word gravity. Gravity is the name associated with the mishaps of the milk spilled from the breakfast table to the kitchen floor and the youngster who topples to the pavement as the grand finale of the first bicycle ride. Gravity is the name associated with the reason for "what goes up, must come down," whether it be the baseball hit in the neighborhood sandlot game or the child happily jumping on the backyard mini-trampoline. We all know of the word gravity - it is the thing that causes objects to fall to Earth. Yet the role of physics is to do more than to associate words with phenomenon. The role of physics is to explain phenomenon in terms of underlying principles. The goal is to explain phenomenon in terms of principles that are so universal that they are capable of explaining more than a single phenomenon but a wealth of phenomenon in a consistent manner. Thus, a student's conception of gravity must grow in sophistication to the point that it becomes more than a mere name associated with falling phenomenon. Gravity must be understood in terms of its cause, its source, and its far-reaching implications on the structure and the motion of the objects in the universe.
Certainly gravity is a force that exists between the Earth and the objects that are near it. As you stand upon the Earth, you experience this force. We have become accustomed to calling it the force of gravity and have even represented it by the symbol Fgrav. Most students of physics progress at least to this level of sophistication concerning the notion of gravity. This same force of gravity acts upon our bodies as we jump upwards from the Earth. As we rise upwards after our jump, the force of gravity slows us down. And as we fall back to Earth after reaching the peak of our motion, the force of gravity speeds us up. In this sense, the force gravity causes an acceleration of our bodies during this brief trip away from the earth's surface and back. In fact, many students of physics have become accustomed to referring to the actual acceleration of such an object as the acceleration of gravity. Not to be confused with the force of gravity (Fgrav), the acceleration of gravity (g) is the acceleration experienced by an object when the only force acting upon it is the force of gravity. On and near Earth's surface, the value for the acceleration of gravity is approximately 9.8 m/s/s. It is the same acceleration value for all objects, regardless of their mass (and assuming that the only significant force is gravity). Many students of physics progress this far in their understanding of the notion of gravity.
In Lesson 3, we will build on this understanding of gravitation, making an attempt to understand the nature of this force. Many questions will be asked: How and by whom was gravity discovered? What is the cause of this force that we refer to with the name of gravity? What variables affect the actual value of the force of gravity? Why does the force of gravity acting upon an object depend upon the location of the object relative to the Earth? How does gravity affect objects that are far beyond the surface of the Earth? How far-reaching is gravity's influence? And is the force of gravity that attracts my body to the Earth related to the force of gravity between the planets and the Sun? These are the questions that will be pursued. And if you can successfully answer them, then the sophistication of your understanding has extended beyond the point of merely associating the name "gravity" with falling phenomenon.
