# Blog

## Soma cube

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The soma cube is a tricky puzzle! First, you’ll glue some cubes together into strange shapes. Then see if you can get those shapes to come together!

Safety: This activity uses hot glue. Ask an adult to help. Before you start, make sure there’s a sink nearby. If you burn yourself, hold the burn under cold, running water for 20 minutes.

### You will need

• 27 small cubes – cheap dice are good
• Hot melt glue

### Making the puzzle

1. This puzzle consists of 7 pieces arranged to form one large cube. Each piece is made of 3 or 4 smaller cubes glued to form shapes.
2. Clean your cubes with detergent, and dry them thoroughly – this will make the glue stick better.
3. Stick 3 cubes together in a straight line. Then stick a fourth cube to the side of the end cube. This piece looks like an ‘L’.
4. Stick 3 cubes together in a straight line. Then stick a fourth cube to the side of the middle cube. This piece looks a bit like a ‘T’.
5. Stick 2 cubes side by side. Then, stick another cube on the top of one of the cubes. This piece looks like a short ‘L’, and only uses 3 cubes.
6. Stick 2 cubes side by side. Stick another cube to the top of the right hand cube. Finally, stick a cube to the right of the top cube. This shape looks a bit like an ‘S’.
7. The remaining 3 pieces are a bit more complicated. Start by making 3 short ‘L’ pieces out of 3 cubes each. Then arrange them so they are all lying flat, and facing the same way.
8. On each short ‘L’, glue an extra cube on a different cube in the ‘L’. You will now have 3 shapes, each made of 4 cubes. Two of them will look like mirror images of each other.

### The Soma cube

• Using the 7 pieces you have made, make a large cube. The large cube will be 3 small cubes wide, 3 deep and 3 tall.

### What’s happening?

This puzzle can be hard, but if you keep trying, you will find the answer. Many people find it easier if they put the more complicated parts together first.

The final solution is a cube with 8 corners. There are only 7 pieces, so at least one piece has to be in 2 corners at once. There are only 2 pieces that can go in 2 corners – the long ‘L’ and the ‘T’, so at least one of these pieces has to go in 2 corners.

There are 2 twisty pieces that look very similar. These 2 are called the ‘left screw’ and the ‘right screw’. These 2 are mirror images of each other, but one twists left, and the other twists right. Any shape that is not the same as its mirror reflection is called a chiral shape. Many other shapes are chiral, including snail shells and DNA.

A list of Soma cube pieces

Soma cube solution (video) [External link]

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## One response

1. Richard Manderson

Here’s a game I invented using the soma pieces (‘Soma-stack’?) : take turns to add to a construction that always stays within a cubic 3x3x3 space. The last person who can add to the construction wins. Of course the maximum number of pieces that could be used in this game is all seven, forming a complete cube. But can you see how to achieve the minimum game that uses just 3 blocks? There are a few ways. It seems that they all share an interesting feature relating to the centre of the cube!

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