This interesting enigma was first published in the second issue of
The Soma Addict. There is said to be a way to form the cube
in which it can be stood atop a "pedestal" no wider than the bottom
center cube. Can you find this solution?!?
Now, there are actually three ways of understanding this challenge.
Make a 3x3x3 cube and balance it on a stick, touching only the center bottom cube. This chapter
Make a 3x3x3 cube with a missing cube, having the missing cube protrude at the bottom as a balance pin. Balancing SOMA on its own piece
Or, make another figure, having 1 (or 2) cube's protruding at the bottom, as balance pin's (No article about this - yet)
For historical reasons, the texts in this chapter do not destinguish between the two first methods.
And I have NO examples of the third method (Maybe you could find some ??)
The Balancing Soma Cube
This information has been updated several times, Follow the
chronological additions to this article.
This interesting information about the Soma Cube was published
in Martin Gardner's Mathematical Games column in July, 1969.
Martin Gardner notes in the article that there are 240 different
ways the cube can be formed not counting rotations and reflections
as being different. This figure was established in 1962 by
John Conway and M.J.T. Guy, who were mathematicians at
the University of Cambridge.
In analyzing his work, Conway discovered the curious fact that only
one of the 240 solutions allows the Soma cube to be balanced on a
pedistal that touches only the central square of the cube's 3 by
3 unit base. This solution is diagrammed below. The central square
of the bottom layer is the one that rests on the pedistal.
Addendum:
The following additional solution to the balancing cube has been
produced by Stuart Collins of Nottingham, UK in June, 1998
and refutes Conway's uniqueness assertion stated above!
Are there more solutions to this problem? Mr. Collins
conjectures that any of the flat 4-cube pieces ( 2,3, and 4 ) might
serve as the balance piece. It only remains to be shown that the
3 piece can serve this function.
Now at 12.1.2000 My friend Courtney McFarren wrote to me:
"I borrowed a book from the Library about puzzles.
It had a few pages on the Soma cube, and showed two new
ways to construct the 3x3x3 cube so you can balance
it on the bottom-center cube:
551 466 226
751 451 426
773 733 423
and
166 446 244
117 356 222
377 357 355
...I tried it both ways. It really works!
Now at 26.8.2002 Steven Mai wrote to me:
"Here are the solutions for the cube that can be supported
on the centre of the base without the cube breaking up.
Interestingly enough, John Conway's solution which he thought was unique was the ONLY solution which I had NOT already found!
It is #13 on the chart.
Note that Stuart Collins' cube is my #3;
The two ways found by Courtney are my #9 and #7 (see its reflection)
And the two found by Steven Mai are my #6 and #5 respectively.
When I first visited Science World BC in Vancouver BC Canada, they had a soma set and a pedestal
with the challenge and the claim that their exists only one solution, but without revealing what
it was; and I played with it and found my solution #1 (and notice piece 7 rests on the pedestal!!)
and I thought that was it.
An assembled a soma cube of my own, rested it on a pedestal at home, and challenged a friend of mine,
Dan Seafeldt, who found what I list as solution #2. Since then, I found the other solutions listed above.
Now at 17.11.2011 Michael Sundermann
has sent me a mail
reporting two more ways to make the balancing SOMA cube. (and its mirror image)
As he wrote: "I want to add two solutions where the 3-piece is at the bottom."
Solution #1 is (No.33 in N990201) and Solution #2r is (No.53 in N990201).
Interestingly, if you inspect the total number of solutions for the SOMA cube.
Found in N990201.HTM "Winning Ways for your mathematical plays"
You find that there are 23 ways to place the '3' piece such that the 'leg of the T' is
at the center position of the bottom slice.
This of course raises the question. Are there more stable combinations.?
What if a solution with the '3' piece at the top is rotated 180 degrees.? etc.
In any case. Two more solutions is great.
Are there any more of them??
The way this list of 240 solutions was found is described at
N030518.HTM "The complete SOMAP is found"
A complete analysis of balanzing
At 15.11.2012 I received this interesting addition to the special shape of a balanzing SOMA.
Hartwig Beusch
has added the following information telling us that 'all' pieces may be the supporting elements.
PS: Hartwig expanded the text a few days later, making it even more complete. Hartwig wrote. (Translated from German)
In your web page [note: This page] you presented solutions for
pieces 1, 3, 4 and 7.
Now using the mirrorimage of the piece 6, even the piece 5 can be the
base of the balancing SOMA cube. This result did surprise me.
But following this, every piece can now be used as base to produce a balancing SOMA cube."
Here are the examples for:
How about checkered solutions then?? - Do solution count change with pattern.?
The balanzing SOMA cube is possible for the pieces 1, -, 3, 4, 5, 6, 7
using the checkered constellation Satz-Ls. In these solutions the piece #2
have a black "hook" and is hanging.
Whereas the balanzing SOMA for piece #2 is possible, only using the
checkered constellation Satz-Lw, where piece #2 have a white "hook" and
carry the figure.
Using the Satz-Ls it is possible to build 240-21 = 219 SOMAcubes. The Satz-Lw allow 21 SOMAcubes.
The white "hook" of piece 2 is blocking the use of this piece as an edge of a SOMAcube.
So - in total, the pieces that carry our SOMAcube are capable of creating a total of:
(For pieces 1 through 7) 1 + 13 + 2 + 8 + 1 + 1 + 1 = 27 solutions (Not counting mirror solutions)
If we include mirrors, there are 52 solutions, as the pieces 5 and 6 exchange positions during the mirroring.
It is interesting that the piece#2 is either a carrier (in 13 cases) or
is hanging (in 14 cases). When hanging, it will run along a vertical corner
holding on at the top using its "hook"
Finally a few tips for the construction of the balanzing SOMA.
1. Place one of the pieces 1 through 7 on the center of the Base.
2. Place the following pieces so that they cannot fall, and settle in place.
3. Keep to the saying "Where shall it go, and how do we keep it there.
Let's see a Video.
Now we know that it is indeed possible to find a SOMA solution, that
will balance on its bottom center cube, so here's a video.
He start by showing a normal cube solution, then destroy it, and show us that a cube
can be built and placed on a pedestal.
The video is from "Hong Kong Middle School - Infinite creativity, toys exhibition."
(I dont understand the language, so I dont really know what he is saying though.)
To see this movie, press the ▶ in the left side of this picture.
So, I challenged myself to find a way to balance the blocks with one center point down
and one empty space in the otherwise 3x3x3 cube.
Attached are pictures that should allow you to see the solution.
I was at a house where they owned a SOMA cube. I do not own one, so I'm unable to further test.
I understand that this puts the empty square on the top row in a different spot than the middle
(so therefore, perhaps this is a different puzzle altogether), but it does balance with only a center square touching.
Let me know what you think!
Hi Matt: This is a very fine solution. The question of course is "What is a balancing SOMA".
Your idea of following up upon the #166, balancing on one center cube,
and - of course - leaving a hole somewhere... IS great.
Now - Can anyone find more of these figures ?
More Balancing on the puzzle cubes & Analysis
Now it is 28.08.2016 - A mail arrived from Hartwig Beusch <beuschdrbe@aol.com>
To my question "Can you find more of these figures?" the answer was simply "Yes, I can."
Ps. Note: These figures were originally drawn with the bottom upwards, it might be easier to build that way.
How do I get such a balanced cube?
The carrier piece 3 "T" consists of the four individual cubes
[ 3A | 3B | 3C ][ 3D ]
The whole construction is resting on the pedestal made of cube 3D, and in the first Example 1:
3A carry piece 6
3B carry piece 5
3C carry piece 4
This is the principle!
If 3A, 3B or 3C, is not used as a carrier for three different pieces, there will be no balanced cube.
Mirroring is subject to other cubes. piece 5 is then changed into piece 6, and 6 to 5.
If the first 3 pieces are placed according to my principle, then the remaining can sometimes be placed in 2 various ways.
The resulting gap is always in a corner.
If the gap is placed in the middle of a side or in the center of the upper layer,
then it is no longer possible to make a balanced cube.
In the next figures we can see:
B1 - B4 The gap may also occur in the lower layer on a corner.
B5 - B10 The gap may also occur in the uppermost layer on a corner.
B6 is identical to B5 , with the exception of the direction of pieces in the upper level.
B1 is the same as C2 except that the piece 7 is rotated.
As mentioned, the crossbeam of piece 3 "T" is called 3A, 3B and 3C.
When we want to balance the cube, then we must select a different piece to place on the 3A, 3B, 3C cubes.
This selection must be from pieces 4, 5, 6 or 7 ("Z, A, B, P")
And pieces 4 and 7 may not occur at the same side.
Thorleifs note: If they do, they will produce a hole in the middle and basically end unstable.
This only allow us the combinations of 4-5-6 and 5-6-7.
A result is only obtained when the gap is selected as the cornerstone of the first or third level.
Gaps in the center of a level or the middle of a side can not be constructed.
We have 4 different positions for a selected gap in the lower level.
But there are 5 different solutions in the upper level.
Because the cube have 4 vertices (corners) in the lower and upper level,
then we find 4x4 + 4x5 = 36 different solutions.
I will now give the 5 solutions having the gap on the top left.
Note: C2 = B1 except for the direction of the 7 "P" piece.
Now these 5 solutions for a gap in the top level are all based on the bottom pattern:
Additional notes
The pieces 1 and 2 ("v and L") are not suitable for the foundation, they will slide off the construction.
This can be realized by studying the patterns in the upper level.
. 1 1 or . 2 2 vertically and horizontally
This pattern occur together in the upper level, when a solution is found.
Now the 4 solutions for a gap in the lower level, all based on the bottom pattern:
Hartwig Beusch: "I find that constructing these cubes is particularly fun and quickly leads to success, if the specified rules are followed."
We are now in 201609 - and the story continue.
Hartwig Beusch: "A neighbour wanted to balance the SOMA cube on piece 4, which is of course not possible.
So I immediately thought of my carrier theory, and thought piece 7 could be used.
I found 5 solutions"
Here are the 5 solutions using piece 7 as carrier:
In some way I feel that these solutions using piece 7 is easier to make, compared to piece 3.
I would also assume more than 9 solutions - as with piece 3.
And the holes are now not limited to the corners. (Maybe I have exchanged pieces 5 and 6)
2017.08.19 Hartwig Beusch: So far the missing cubes heve been located in the corners, or a few times at an edge.
However, having a hole at the top center is also an option. Here are 5 solutions.
Hartwig Beusch: "Oh - This solution was unexpected E6. :-)"
2016.09.15: A balancing SOMA on piece 7 with hole in the center !!! Note: The two solutions E6 and E7 are shown with their mirror symmetrical solutions.
However, there are no other solutions for this particular position of pieces 7 and 6 and,
to find all solutions we should maybe look at the possible positions of pieces 6 and 5 relating to carrier piece 7.
There seem to be a very high number of solutions.
Hartwig Beusch: "In the meantime I have considered the problem of balancing on piece 7."
So. Solutions in which piece 5 occurs are formed by rotation and reflections.
There are no solutions in which piece 5 or 6 does not occur.
Case 1 .........................................
Case 1 was then investigated more closely. There are probably 67 solutions.
The number of solutions depends on the location of the gap.
X means: that this cube is occupied by stone 7 or 6.
Where the gap is, I have written the number of possible solutions.
Zero indicates that there is no construction with a hole at this position.
level: Top Midt Low Balance
Solutions: 20 12 35
5 2 4 6 2 4 X 2 1 0 0 0
0 0 6 X X 0 X X X 0 - 0
0 3 0 0 0 0 23 X 9 0 0 0
Case 2 .........................................
I have also investigated case 2, There are 80 different solutions.
So here are the number of solutions for each hole in Case 2:
level: Top Midt Low Balance
Solutions: 20 10 50
4 0 2 6 0 0 8 21 10 0 0 0
2 0 3 2 2 0 X X X 0 - 0
4 5 0 X X 0 X X 11 0 0 0
Again a total of 80 solutione.
So now to a definition for [Balanced]:
There can be no pieces in the lower levels, unless they are hanging.
In this example:
- - -
6 7 7
6 7 -
Due to pieces 6 7 - no piece can fall.
In the combination - - - we do NOT allow 2 2 2, - 2 2, - 1 1, 3 3 3, 4 4 -
as these pieces find no hold. At 6 7 - no stone can fall.
If I take both Case 2 and Case 1, then stone 7 will allow a total of 67 + 80 = 147 different Balanced cubes.
This piece is therefore more suitable than piece 3, which allow only 9 solutions.
So starting with Case 1 and Case 2 then we find only half of the solutions.
- 3 - 6 3 -
6 3 - 6 3 -
6 3 - - - -
And we then have to examine Case 3 and Case 4
- 3 - 5 3 -
5 3 - 5 3 -
5 3 - - 3 -
In the image below you will find all the solutions with a gap in the lower level.
They fold into each other through reflections. Whereas Rotations do not bring new constellations.
- submitted by Martin Gardner - (The initial question)
- submitted by Stuart Collins
- submitted by Courtney McFarren
- submitted by Steven Mai
- submitted by Jim Waters
- submitted by Michael Sundermann
- submitted by Hartwig Beusch - (A complete analysis of balanzing)
- submitted by Matt Esser - (Balancing SOMA on its own piece)
- submitted by Hartwig Beusch - (More Balancing on the puzzle cubes & Analysis)
- User entries have been carefully edited by Thorleif Bundgård.