New machine unfriendly £1 coin

Vending machines identify coins by measuring their width. Circular coins have the same width in every direction, so designers of vending machines do not need to worry about incorrectly rotated coins causing a blockage or being misidentified. But what about seven-sided 20p and 50p coins?
Perhaps surprisingly, 20p and 50p coins also have a constant width, as show by this video. In fact, the sides of any regular shape with an odd number of sides can be curved to give the shape a constant width.
3, 5, 7 and 9 sided shapes of constant width.
Today, a new 12-sided £1 coin was unveiled. One reason for the number of sides was to make the coin easily identified by touch. However, as only polygons with an odd number of sides can be made into shapes of constant width, this new coin will have a different width when measured corner to corner or side to side. This could lead to vending machines not recognising coins unless a new mechanism is added to correctly align the coin before measuring.
Perhaps an 11-sided or 13-sided design would be a better idea, as this would be easily distinguishable from other coins by touch which being a constant width to allow machines to identify it.

Similar posts

The end of coins of constant width
New machine unfriendly £1 coin, pt. 2
World Cup stickers 2018, pt. 3
World Cup stickers 2018, pt. 2


Comments in green were written by me. Comments in blue were not written by me.
 Add a Comment 

I will only use your email address to reply to your comment (if a reply is needed).

Allowed HTML tags: <br> <a> <small> <b> <i> <s> <sup> <sub> <u> <spoiler> <ul> <ol> <li>
To prove you are not a spam bot, please type "m" then "e" then "d" then "i" then "a" then "n" in the box below (case sensitive):


Show me a random blog post

May 2020

A surprising fact about quadrilaterals
Interesting tautologies

Mar 2020

Log-scaled axes

Feb 2020

PhD thesis, chapter ∞
PhD thesis, chapter 5
PhD thesis, chapter 4
PhD thesis, chapter 3
Inverting a matrix
PhD thesis, chapter 2

Jan 2020

PhD thesis, chapter 1
Gaussian elimination
Matrix multiplication
Christmas (2019) is over
▼ show ▼
▼ show ▼
▼ show ▼
▼ show ▼
▼ show ▼
▼ show ▼
▼ show ▼
▼ show ▼


folding tube maps pizza cutting statistics determinants matrix of cofactors electromagnetic field probability london logs royal institution simultaneous equations latex preconditioning graph theory football mathslogicbot programming bempp gerry anderson countdown sorting graphs nine men's morris ternary chalkdust magazine computational complexity advent calendar video games menace bodmas arithmetic inline code dataset quadrilaterals harriss spiral map projections exponential growth inverse matrices mathsteroids radio 4 reddit stickers php big internet math-off mathsjam noughts and crosses phd twitter manchester science festival finite element method sport talking maths in public misleading statistics tmip flexagons numerical analysis error bars the aperiodical data puzzles golden ratio dragon curves accuracy braiding royal baby european cup game of life draughts hannah fry national lottery rhombicuboctahedron hats realhats books world cup chess platonic solids pythagoras reuleaux polygons cross stitch bubble bobble speed tennis matrix of minors convergence london underground weak imposition hexapawn wave scattering raspberry pi estimation trigonometry christmas card news fractals binary christmas python ucl oeis wool craft weather station golden spiral captain scarlet geometry squares people maths approximation javascript martin gardner folding paper final fantasy logic propositional calculus sound triangles rugby light frobel machine learning manchester go data visualisation matrices palindromes games signorini conditions chebyshev game show probability pac-man matt parker curvature asteroids geogebra dates a gamut of games interpolation matrix multiplication sobolev spaces cambridge coins polynomials boundary element methods plastic ratio gaussian elimination


Show me a random blog post
▼ show ▼
© Matthew Scroggs 2012–2020