Posts

2020-05-04: Archimedes and the sphere

2019-05-16: Glow worms return

2019-04-11: Original memetic sin

2019-01-31: The theory of weight

2018-11-06: Origins of telephone network theory

2018-10-24: Modern thought

2018-09-10: Feeding a controversy

2018-06-11: Glow worm distribution

2018-04-23: Outlawing risk

2017-08-22: A rebuttal on the beauty in applying math

2017-04-22: Free googles book library

2016-11-02: In search of Theodore von Karman

2016-09-25: Amath Timeline

2016-02-24: Math errors and risk reporting

2016-02-20: Apple VS FBI

2016-02-19: More Zika may be better than less

2016-02-17: Dependent Non-Commuting Random Variable Systems

2016-01-14: Life at the multifurcation

2015-09-28: AI ain't that smart

2015-06-24: MathEpi citation tree

2015-03-31: Too much STEM is bad

2015-03-24: Dawn of the CRISPR age

2015-02-12: A Comment on How Biased Dispersal can Preclude Competitive Exclusion

2015-02-09: Hamilton's selfish-herd paradox

2015-02-08: Risks and values of microparasite research

2014-11-10: Vaccine mandates and bioethics

2014-10-18: Ebola, travel, president

2014-10-17: Ebola comments

2014-10-12: Ebola numbers

2014-09-23: More stochastic than?

2014-08-17: Feynman's missing method for third-orders?

2014-07-31: CIA spies even on congress

2014-07-16: Rehm on vaccines

2014-06-21: Kurtosis, 4th order diffusion, and wave speed

2014-06-20: Random dispersal speeds invasions

2014-05-06: Preservation of information asymetry in Academia

2014-04-16: Dual numbers are really just calculus infinitessimals

2014-04-14: More on fairer markets

2014-03-18: It's a mad mad mad mad prisoner's dilemma

2014-03-05: Integration techniques: Fourier--Laplace Commutation

2014-02-25: Fiber-bundles for root-polishing in two dimensions

2014-02-17: Is life a simulation or a dream?

2014-01-30: PSU should be infosocialist

2014-01-12: The dark house of math

2014-01-11: Inconsistencies hinder pylab adoption

2013-12-24: Cuvier and the birth of extinction

2013-12-17: Risk Resonance

2013-12-15: The cult of the Levy flight

2013-12-09: 2013 Flu Shots at PSU

2013-12-02: Amazon sucker-punches 60 minutes

2013-11-26: Zombies are REAL, Dr. Tyson!

2013-11-22: Crying wolf over synthetic biology?

2013-11-21: Tilting Drake's Equation

2013-11-18: Why $1^\infty != 1$

2013-11-15: Adobe leaks of PSU data + NSA success accounting

2013-11-14: 60 Minutes misreport on Benghazi

2013-11-11: Making fairer trading markets

2013-11-10: L'Hopital's Rule for Multidimensional Systems

2013-11-09: Using infinitessimals in vector calculus

2013-11-08: Functional Calculus

2013-11-03: Elementary mathematical theory of the health poverty trap

2013-11-02: Proof of the circle area formula using elementary methods

Archimedes and the sphere

When preparing some homework answers recently, I rediscovered a simple geometric fact that had escaped my attention in the past. If you have a ball, and place this ball in side the smallest can that is large enough to hold it and be sealed, the outside of the can, minus the top and bottom lids, has the exact same area as the ball inside! This is easy to check with the well-known formulas for the areas of spheres and cylinders. Not just that. If you slice the can into two parts with a level cut, in both cases, the area of the outside of that part of the can (minus the lid) will equal the outside area of the part of the ball left inside! This is a really rather remarkable coincidence (of course, I mean coincidence in the sense of coinciding, not in the sense of "lucky", because it's math after all). One of the reasons it may have escaped me is that this is a purely mathematical result that can not be applied in reality because solid materials are not fluidly deformable -- with a little experimentation, we learn that if you want to completely cover an orange in tinfoil, the tinfoil MUST BE longer than the height of the sphere, but you'll always have wrinkles when you do so.

This equality of areas reminded me of a result of Archimedes, which I'd heard the story of, but had never found so impressive. On looking it up, it seems that On the sphere and the cylinder does indeed include the first half of this result, atleast in its classical form.

However, now I'm curious if his results imply the second of these considerations as well -- Did Archimedes also know about the equality of areas of the sliced cylinder and sphere sections? In my opinion, that would have been quite a splendid discovery, and worthy of a grave stone.