A domino is a flat thumb-sized rectangular block, typically twice as wide as it is tall, that bears one to six spots or pips on either side. A complete set of dominoes contains 28 such tiles, which are also called bones, cards, men, or pieces. Dominoes are used to play a variety of games in which players place tiles down in lines and angular patterns to create a chain reaction that results in the knocking over of all remaining tiles. In the past, European-style domino sets were made from bone, silver lip ocean pearl oyster shell (mother of pearl), ivory, and dark hardwoods such as ebony. Modern sets are often made from polymer materials.
A player begins a game by drawing the number of tiles specified in the rules of the specific game, and placing them on the table in front of him. Then he starts the game by playing the first tile, which is referred to as “the set,” “the down,” or the “lead.” Depending on the rules of the particular game, this may be done either by drawing a tile from your hand or by placing the tile over another one that you already have.
Each tile has two ends, which are distinguished from each other by the value of the pips on each end. Each end has a different value, from six pips at the highest to none or blank at the lowest. The sum of the values on each end is known as the rank or weight of a domino, and the ranking of a tile helps determine its suitability for play.
As each tile is placed, it joins a line of tiles that are joined together by matching the open ends of adjacent dominoes. This configuration of dominoes is known as the line of play, and there are basic instructions for this that are listed here under Line of Play. Generally, doubles are played crosswise over the line of play, and singles are played lengthwise.
If a player has no matching tiles in his hand, or if he plays a tile out of turn, he must draw new hands and return to his original position. He may then play again if he can, but otherwise the next player takes his turn.
Physicist Stephen Morris, who has studied the energy of dominoes, explains that when you stand a domino upright, it stores some potential energy based on its position. When you then knock it over, most of this potential energy is converted into kinetic energy as the domino moves down the line.
A famous example of this phenomenon is the Domino Effect, which was coined in the early 1970s by columnist Alsop to explain how America’s support of South Vietnam could lead to Communism spreading throughout the region. The idiom has since been applied to any scenario in which one small trigger can start a series of events that continue to grow and build upon each other, like a domino falling over.