### Cylindrical Lens Puzzle

A similar puzzle (but taking advantage of horizontal symmetry) available here:

From Educational Innovations: **BUY NOW Cylindrical Lens Puzzle **

Cylindrical Lens Puzzle: this cylinder of acrylic acts as lens that focuses light along a line rather than a point- and thus it can invert an image along its symmetry axis. Puzzle question: the word "GREEN" is flipped by this lens but the word "TOMATO" seems unaffected. Is the physics significantly different for red wavelengths as compare to green? Or is there another explanation/trick? Answer below.

### Puzzle Proofs

Get these and many other interesting puzzles here:

From Etsy: **BUY NOW**: **Puzzles from Jeux Efce**

Puzzle Proofs: three mathematical proofs in a physical form that use equivalent areas to make the case. The first video illustrates one of the most famous equations concerning the sides of any right triangle, the Pythagorean Theorem. The area of a square with side c of the hypotenuse is indeed equal to the sum of the areas of the squares of side a and b. One of the most used formulas when calculating vectors in physics classes! In the second video, similar comparisons of areas illustrate two special binomial products (a+b)² and (a+b)(a-b), and connects these famous algebraic equations to simple geometry.

### Aqua Drop Puzzle

Three models/colors to choose from:

From Amazon: **BUY NOW Aqua Drop Puzzles **

From eBay: **BUY NOW: Aqua Drop Puzzle**

Aqua Drop Puzzle: a superhydrophobic coating allows this dexterity puzzle to use a drop of water as the "pinball". The white surface is a silica nano-coating that makes water roll off- a condition sometimes referred to as the Lotus effect because leaves of the Lotus plant have this property.

### Magnetic Cube

Many colors to choose from:

From MagneticCube.com: **BUY NOW Magnetic Dice Cube **

See also the original indestructibles post: Magnetic Acrylic Rubik's Cube

Magnetic Cube: a twisty Rubik’s Cube puzzle made from 27 dice and 108 neodymium magnets. This cube includes the scrambled states and solutions of the original 3x3 Rubik’s Cube but is held together only by magnets! The magnets, in this special configuration, lock the dice together with a satisfying click upon rotation. This beautiful cube was produced by Owen Lillywhite of magneticcube.com and is based on a gfixler design posted on instructables.

### Pythagorean Puzzle

Available here:

From Creative Crafthouse:** BUY NOW Pythagorean Puzzle**

Pythagorean Puzzle: a proof, in physical form, of one of the most famous equations concerning the sides of any right triangle. The area of a square with side c of the hypotenuse is indeed equal to the sum of the areas of the squares of side a and b. This kit also allows at least two other ways to prove this theorem named after the famous Greek mathematician from 500 BC. One of the most used formulas when calculating vectors in physics classes ?

### Impossible Jar with Golf Ball

Get this "impossible" jar and other amazing things from this shop:

From Etsy: **BUY NOW: Impossible Jar & Golf Ball**

Impossible Jar with Golf Ball: a regular off the shelf golf ball somehow trapped within a standard glass jar. Neither the ball nor the jar were cut or glued in the fabrication process. The puzzle aspect is to consider how this object was produced (again, I have some theories- but I do not know the secrets of this artist). This incredible piece was made by craftsman and artist Nathan Nickerson, and comes with the golf tee display stand (a nice touch!)

### Hydrophobic Water Maze

Wonderfully well crafted and available from this shop :

From Etsy store TheSmallestWorkshop:

**BUY NOW Hydrophobic Water Maze**

Hydrophobic Water Maze: a superhydrophobic coating allows this dynamic puzzle to use a drop of water as the "pinball", which can split into multiple smaller drops and recombine along the way. The wood surface is treated with silica nano-coating that makes water roll off- a condition sometimes referred to as the Lotus effect because leaves of the Lotus plant have this property.

### Magic Sand Wand Puzzle

This puzzle was produced in the 1990s, sometimes found on eBay (currently two avialable):

From eBay: **SEARCH NOW: Magic Sand Wand Puzzle**

Wikipedia has a good introduction to the possible mechanisms of the Brazil nut effect

Magic Sand Wand Puzzle: this week’s physics brain teaser- move the steel ball through the sand to the other end of the tube. Amazingly it can be done in less than 6 seconds! Hint: spinning won’t help this time. The solution to this vintage puzzle relies on some interesting physics concerning granular convection. Answer below and swipe to reveal solution.

### 3D Pentominoes

The set I used for this video is called *Pocket Katamino* and is available here

From Amazon:** BUY NOW Pentominoes **

3D Pentominoes: the 12 possible arrangements of five identical squares, joined edge to edge, form the set of all pentominoes. Since 12x5=60, the pentominoes can tile a 6 x 10 rectangle with no gaps (2339 ways to do this- yet even finding one solution is a challenge). This set of colorful pentominoes is made so that the height of each piece is the same as the width of the constituent squares, such that 3D constructions can be made. Since 3x4x5=60 one can build a box with these dimensions (amazingly, 3940 ways to do this- but again, finding one is still a fun challenge).

### Square Dissection Puzzles

Get these and other well made disection puzzles here:

From Etsy: **BUY NOW: Square Dissection Puzzles**

These puzzles are expertly laser cut and sold by GamesEfce. I spray-painted the pieces of mine to better show the shapes and relationships for the video.

Square Dissection Puzzles: a square can be cut (dissected) into polygons and then reassembled into other regular polygons. Shown here: an equilateral triangle, a pentagon, and a hexagon. These are the record holders for smallest number of pieces needed: triangle (4 pieces by Henry Dudeney 1902), hexagon (5 pieces Paul Busschop 1870s) and pentagon (6 pieces Robert Brodie 1891). Fun fact- It is not known if any of these records are the smallest possible, no mathematical proofs yet exist on this question.

### Sphere Sticks Geometric Puzzle

Get this affordable and amazing puzzle here:

From Etsy: **BUY NOW: Sphere Sticks**

Sphere Sticks Puzzle: 30 identical wood pieces, each with two notches as shown, can create 12 interlocking pentagons in a perfect symmetry- look carefully and you can see that each rod is in an identical configuration with the 4 others that connect with it. Precision cut notches on the rods allow them to interlock with elastic tension such that vector sum of the 4 forces sum to zero in this tensegrity type equilibrium. The dodecahedron, with its 30 edges and 12 sides, is the basis of this puzzle sculpture.

### Soma and Rhoma Puzzles

The Rhoma Cube is a vintage item and can sometimes be found on eBay:

From eBay: **Search NOW: Rhoma and Soma Puzzles**

Soma Cubes are available in a wide viariety:

From Amazon: **BUY NOW: Soma Cube**

From Etsy: **BUY NOW: Soma Cube**

SOMA and RHOMA Puzzles: Replace every cube in the Soma puzzle with a rhombohedron to create the Rhoma puzzle- where the seven slanted pieces now make a larger rhombohedron. Here I’ve painted the corresponding Soma and Rhoma pieces to match on these sister puzzles that share identical edge lengths. While there are 240 ways to make the larger cube from the 7 Soma pieces, there is only one solution for the 7 Rhoma pieces. The original Soma Cube is a math toy has an interesting connection to physics- invented by Danish scientist and artist Piet Hein who claimed that this puzzle idea came to him as he was listening to a lecture on Quantum Mechanics by Werner Heisenberg in 1933. The seven pieces are all the ways 3 or 4 cubes can be joined, such that each piece has at least one inside corner.

### Cone of Apollonius

Similar models available here:

From Etsy: **BUY NOW: Cone of Apollonius**

Cone of Apollonius: Slicing a cone with a plane will produce the famous curves known as the conic sections, as demonstrated with this beautiful vintage wood model by Nasco. Slicing at a right angle to the cone’s axis of symmetry produces a circle, and tilting the intersecting plane a bit produces an ellipse. When the plane is tilted parallel to the side of the cone the curve produced is a parabola, and tilting even further creates a hyperbola. The discovery of the mathematics demonstrated here are attributed to Apollonius of Perga from about 250 BC- thousands of years later Kepler, Newton, and others showed these conic sections to be intricately connected to many branches of physics such as planetary orbits and the optics of telescopes.

### Impossible Wallet

Available here:

From Amazon: **BUY NOW Magic Wallet **

From eBay: **BUY NOW Magic Wallet**

Impossible Wallet: this pocketbook has a special double hinge that allows the wallet to be opened from either side, and leads to some rather nonintuitive consequences. Note that once inserted, the bill shows the same face independent of which way the wallet is opened. The construction of this magic (or flip) wallet is similar to the famous Jacob's Ladder toy.

### Jacob’s Ladder Image Flip

Available from this shop in Spain:

From Punto Verna: Reproduction Jacob's Ladder

Classic versions of this toy available here:

Amazon:** BUY NOW Jacob's Ladder Toys **

The same ribbon hinge mechanism is used to make the "magic" wallet click here

Jacob’s Ladder Image Flip: with a twist of the wrist this reproduction flips back and forth between an image of Queen Victoria and that of Prince Albert with a satisfying click-clack sound. The earliest description of the ribbon hinge mechanism that creates this kinetic illusion of cascading blocks comes from a magazine article in Scientific American in 1889.

### Rhombic Blocks Mathematical Puzzle

This beautifully made puzzle available here::

From Etsy: **BUY NOW Rhombic Blocks **

Rhombic Blocks Mathematical Puzzle: There are 9 possible ways three rhombuses can be joined together along a common edge, and similar to pentominoes, these 9 tri-rhombs can tile a polyhedron, in this case a hexagon. There are 14 solutions to this puzzle, and one where no same-colored pieces touch. A beautiful math discovery by puzzle master Stuart Coffin.

### Mirror Vision Puzzle

More than three versions of this puzzle out there. Often available here:

From eBay: **BUY NOW: Mirror Vision Puzzle**

Mirror Vision Puzzle: this Harry Potter themed puzzle has only 9 pieces but each supplies two parts of the final image- without the mirror one gets only half the picture. The top of each square is a corrugated lenticular composition of two images, and when viewed from the correct angle only one image can be seen directly, with the other reflected in the mirror, which combine in this case to reveal the famous phoenix bird of the HP stories. Flipping over the puzzle squares produces a second image to solve, this time a basilisk. An ingenious puzzle form from inventor/designer Mark Setteducati and sold by Mattel.