The Rubik's Cube is a puzzle that consists of a handheld cube whose edges are slightly less than 3 inches. The cube seems to be composed of 27 smaller brightly colored cubelets so each face is a 3-by-3 array. Each face of the cube can be turned independently. The puzzle is solved when each face of the cube is a solid color.

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## History

Hungarian architecture professor Enro Rubik invented the best selling toy in the world (current approximation is a half billion sold) in 1974. He invented it to help his students visualize three dimensional rotations. He sold it to Ideal Toys in 1980. The world will celebrate the Rubik's Cube 30th anniversary in 2010.

## Significance

The chief cultural significance of the Rubik's Cube is as a proof of intelligence. It has appeared in dozens of movies as a device for quickly demonstrating a character's intelligence. Besides the problem of solving the puzzle, there is another interesting problem with the cube--the mechanical problem. How is a Rubik's cube made and how do all those pieces work together?

## Construction

Mechanically, the Rubik's cube is partly an illusion. There appear to be 27 identical cubelets, but there are actually only 26 cubelets (no center cubelet) and they are not all identical--there are three different types: six center cubelets with one face each, 12 edge cubelets with two faces each, and eight corner cubelets with three faces each. To disassemble the cube, rotate one face 45 degrees and pry off the exposed corner. Once you remove one of the cublets, the rest follow easily.

## Function

The center cubelets are the framework upon which the rest of the cubelets rotate. The center cublets are the center of each face of the Rubik's cube connected in a fixed three-dimensional cross. The edge cublets are beveled so they can rotate around the center cublets and the corner cublets are cut so that they ride between the edge cublets when you rotate the faces.

## Considerations

The simplest way to see how a Rubik's cube is made is to disassemble it. If you take a reasonable amount of care it snaps back together as good as new. One thing you should be aware of is that if you take apart the cube and don't put each cubelet back in exactly the proper place you might have created a cube that is impossible to solve. To avoid this problem, only disassemble a solved cube--then it is easy to see how to reassemble it.

## Expert Insight

The current world record (as of April 2010) for single time on a Rubik's Cube in an international competition is 7.08 seconds. The world record average solve (average of the middle three of five trials) is currently 9.21 seconds. One of the most amazing events in these competitions is the blindfold solve: the contestant is handed a randomized cube to examine as long as he wants, then blindfolded before doing any rotations. The total time--examination plus blindfolded rotation--is recorded. The current world's record is 32.27 seconds.