Alex Bellos - 50p coin rolling

http://www.bloomsbury.com/alexsadventuresinnumberland
http://alexbellos.com
This is not an optical illusion! When you roll a book on 50p pieces, the book will roll completely smoothly. It does not bob up and down, as you might expect. This is because the shape of a 50p is a curve of constant width, in other words the distance between top and bottom is always the same. This mathematical property of the 50p was fundamental as to why it was introduced in 1969. Since the width is always the same it can be used in coin-operated machines, which determine type of coin by measuring width. The rolling trick also works with 20p pieces too.

It's explained in more detail here
http://alexbellos.com/?p=844


In Alex's Adventures in Numberland, Alex Bellos explodes the myth that maths is best left to the geeks. Covering subjects from adding to algebra, from set theory to statistics, and from logarithms to logical paradoxes, he explains how mathematical ideas underpin just about everything in our lives.

Alex explains the surprising geometry of the 50p piece, and the strategy of how best to gamble it in a casino. He shines a light on the mathematical patterns in nature, and on the peculiar predictability of random behaviour. He eats a potato crisp whose revolutionary shape was unpalatable to the ancient Greeks, and he shows the deep connections between maths, religion and philosophy.

Alex weaves a journey from primary school to university level maths, from ancient history to the computing frontline, and from St Louis, Missouri, to Braintree, Essex. He meets the worlds fastest mental calculators in Germany, consults a numerologist in the US desert, meets a startlingly numerate chimpanzee in Japan, and seeks advice from a venerable Hindu sage in India. An unlikely but exhilarating cocktail of history, reportage and mathematical proofs, Alexs dispatches from Numberland show the world of maths to be a much friendlier and more colourful place than you might have imagined.


Animation © John Downie

Category:

Education

Tags:

• numberland
• mathematics
• alex bellos
• maths
• clever
• Alex's
• Adventures
• in
• Numberland
• 50p
• Bloomsbury Publishing

[chiffmonkey]

@gitaardrum It's showing you that if you place something on a 50p the object will stay at the same altitude as the coin rolls.

[gitaardrum]

dont get it