Schlumberger
 
Drawing the Football
Saved by Symmetry - The Icosahedron

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There is no doubt that when you start to look more closely at the shape of the football it seems pretty complicated, we tend to get lost trying to follow all the patches going around the ball.

However we have a powerful concept to help us - symmetry. It is true that the shape is very complicated but it is very symmetrical - there are lots and lots of repeating patterns. If we can spot these patterns we can make use of it to really see what is going on. We need to understand and appreciate the symmetry because simply trying to remember the pattern is too difficult - hence the understandable difficulty people have had trying to draw it!

The Icosahedron

People have been fascinated by symmetrical shapes for thousands of years. Plato, the famous Greek philosopher, played around with simple 2D shapes such as triangles, squares and pentagons (5 sides) and used them to construct 3D objects.

By just taking triangles for example we can make some wonderfully symmetrical shapes. For example if we take 4 triangles we get a tetrahedron and 20 triangles gives us the icosahedron (see picture of the crystals). In all these wonderfully symmetrical objects all the faces are the same as each other, all the corners are identical to each other and all the edges are the same as every other edge. These are just 2 of the set of 5 famous Platonic solids that have these unusual symmetrical properties.

Platonic solids

The platonic solids (cut-quartz) from left to right: a tetrahedron, cube, octahedron, dodecahedron and the icosahedron. These objects are remarkably symmetrical and in each shape every face, edge and corner are identical with every other face, edge and corner.

The Structure of the Football - The Truncated Icosahedron (!)

The icosahedron has 12 corners and from the picture (below) we can see that there are 5 edges coming out from each and every one. If we imagine that we have a sharp saw and could cut-off each corner (say 1/3 of the way along each edge) it would leave a five sided hole behind - a pentagon.

Icosahedron
Icosahedron:
12 corners
20 triangle faces
30 edges

Icosahedron Icosahedron Icosahedron

Icosahedron
Truncated
Icosahedron:
60 corners
12 pentagons
20 hexagons
90 edges

Truncating the icosahedron.
far left - the icosahedron
far right - the fully truncated icosahedron


If we keep going round the shape, cutting off all the corners, we are doing what mathematicians call truncating the shape. As the icosahedron has 12 corners (each with 5 edges) truncating it produces 12 pentagons.

Also because about a 1/3 of the original edges are left behind (after cutting all the corners) we find that 6 sided shapes - hexagons – appear between these new pentagons. So by truncating the icosahedron we get a truncated icosahedron (!) which has pentagons and hexagons.

The truncated icosahedron is very symmetrical because the original icosahedron was so very symmetrical. Further to this it is exactly the same shape as a football!

 

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Drawing the Football 
The Problem and Examples
Saved by Symmetry - The Icosahedron
Understanding the Structure
The Truncated Icosahedron
The Discovery of Fullerenes
References and Answers
Related Links
 
 

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