As any domino player knows, the success of a chain reaction depends on the careful placement of each piece. The way in which the pieces are lined up, whether they touch or are stacked, and how the next domino is played all contribute to a sequence that ultimately leads to a toppling of the last remaining domino. This is a simple principle, but the rules of domino are complex and vary according to the game being played.
A domino is a rectangular tile bearing an arrangement of spots, or pips, on one face and blank or identically patterned on the other. Each pips represents a number (from zero to nine), as well as the direction in which the tile will fall when struck. Dominoes are typically made of a material such as wood, bone, ivory, or plastic, although some sets are made of natural materials, stone (such as marble and granite), brass, ceramic clay, or even frosted glass.
The most common domino set contains a total of twenty-six double-sided tiles with two matching ends. This is a small number especially when playing with more than four people, so many domino sets are “extended” by introducing ends with greater numbers of spots; this increases the number of unique combinations of ends and thus of pieces. Common extended sets include the double-nine, double-twelve, and double-18.
When a person plays a domino, the first thing they must do is determine who will make the first play of a given game. This is usually determined by the position of each player and the rules of the particular game being played. The player making the first play may also be referred to as the setter, downer, or leader.
Once a player makes the first play, they must then line up the remaining tiles on the table so that their matching ends are adjacent to one another. The shape of the chain that develops from this is at the discretion of the players, and it will depend on the limitations of the table, the type of domino being played, and the number of dominoes being used. A domino must be placed squarely against the tile being played, except when the chain is a double, in which case it should be placed perpendicular to the double touching its center.
The reason that a line of hundreds or thousands of dominoes can all topple with the slightest nudge is because they have inertia, a tendency to remain motionless when no external force is acting on them. However, once the initial domino falls, its potential energy becomes kinetic energy—energy of motion—and is transferred to the next domino as it hits it, sending it crashing into the next and so on. This continues down the chain until the last domino finally crashes to the ground. Hevesh, who has created some of the most mind-blowing domino displays ever seen, explains that her process for creating a design is very similar to the engineering-design approach used in building structures such as bridges or skyscrapers.