Tag Archives: physics

Flat Earther

Eratosthenes calculated the circumference of the Earth without leaving Egypt. He knew that at local noon on the summer solstice in Syene (modern Aswan, Egypt), the Sun was directly overhead. He knew this because the shadow of someone looking down a deep well at that time in Syene blocked the reflection of the Sun on the water. He measured the Sun’s angle of elevation at noon on the same day in Alexandria. The method of measurement was to make a scale drawing of that triangle which included a right angle between a vertical rod and its shadow. This turned out to be about 7°, or 1/50th of the way around a circle. Taking the Earth as spherical, and knowing both the distance and direction of Syene, he concluded that the Earth’s circumference was fifty times that distance.

His knowledge of the size of Egypt was founded on the work of many generations of surveying trips. Pharaonic bookkeepers gave a distance between Syene and Alexandria of 5,000 stadia (a figure that was checked yearly).  Some say that the distance was corroborated by inquiring about the time that it took to travel from Syene to Alexandria by camel. Carl Sagan says that Eratosthenes paid a man to walk and measure the distance. Some claim Eratosthenes used the Olympic stade of 176.4 m, which would imply a circumference of 44,100 km, an error of 10%,[16] but the 184.8 m Italian stade became (300 years later) the most commonly accepted value for the length of the stade,[16] which implies a circumference of 46,100 km, an error of 15%.[16] It was unlikely, even accounting for his extremely primitive measuring tools, that Eratosthenes could have calculated an accurate measurement for the circumference of the Earth. He made three important assumptions (none of which is perfectly accurate):

  1. That the distance between Alexandria and Syene was 5000 stadia,
  2. That the Earth is a perfect sphere.
  3. That light rays emanating from the Sun are parallel.

Eratosthenes later rounded the result to a final value of 700 stadia per degree, which implies a circumference of 252,000 stadia, likely for reasons of calculation simplicity as the larger number is evenly divisible by 60.[16] In 2012, Anthony Abreu Mora repeated Eratosthenes’ calculation with more accurate data; the result was 40,074 km, which is 66 km different (0.16%) from the currently accepted polar circumference of the Earth.

Seventeen hundred years after Eratosthenes’ death, while Christopher Columbus studied what Eratosthenes had written about the size of the Earth, he chose to believe, based on a map by Toscanelli, that the Earth’s circumference was one-third smaller. Had Columbus set sail knowing that Eratosthenes’ larger circumference value was more accurate, he would have known that the place that he made landfall was not Asia, but rather the New World.

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La historia de π (pi)

π is wrong!” by Bob Palais

appeared in

The Mathematical Intelligencer Springer-Verlag New York Volume 23, Number 3, 2001, pp. 7-8.

Bob Palais gratefully acknowledges Dr. Chandler Davis, for his encouragement and editorial input.

(See also the Wikipedia entry on Dr. Davis.) The most amusing letter to the editor in response stated:

“I agree with Bob Palais’ pi-ous article, but it may be 2-pi-ous.”


The Pi Manifesto

 

Last updated July 4th, 2011

– See more at: http://www.thepimanifesto.com/#sthash.R4ubVZpw.dpuf

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What If Everyone JUMPED At Once?

Published on Aug 18, 2012

Follow Michael Stevens http://www.twitter.com/tweetsauce

Tell Geek and Sundry that Vsauce says “hi!” and SUB!:http://www.youtube.com/watch?v=6-Wef0…

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music courtesy of http://www.SoundCloud.com/JakeChudnow

Thanks to:
http://www.youtube.com/phoenixsaintly
and
http://www.youtube.com/theINENIvlogs
For helping me with this video at Summer in the City!!
theINENIvlogs behind the scenes Summer in the City vid with me:http://www.youtube.com/watch?v=F_Rd35…

Why videos views freeze in the 300s on YouTube (sub to this channel FTW, seriously): http://www.youtube.com/watch?v=oIkhga…

Japan Earthquake and Earth’s rotation:http://en.wikipedia.org/wiki/2011_T%C…

All people in one place LIVING:http://persquaremile.com/2011/01/18/i…

shoulder-to-shoulder: http://news.nationalgeographic.com/ne…

BBC Jump Video: http://www.bbc.co.uk/learningzone/cli…

SCALE OF UNIVERSE AWESOME: http://htwins.net/scale2/

STRAIGHTDOPE article on a jump:http://www.straightdope.com/columns/r…

Dot Physics on the jump: http://www.wired.com/wiredscience/201…

Interactive scale of the universe: http://scaleofuniverse.com/

Decimate: http://www.etymonline.com/index.php?a…

Dunbar’s Number: http://en.wikipedia.org/wiki/Dunbar&#…

NPR story on Dunbar’s number:http://www.npr.org/2011/06/04/1367233…

Life Expectency: http://en.wikipedia.org/wiki/Life_exp…

How many people you meet in your life:http://eclectic24.wordpress.com/2009/…

Newton’s Third Law: http://www.physicsclassroom.com/class…