Domino is a game in which players try to get their dominoes into a line before their opponents. Each domino has a number of spots, or pips, on one end, and is blank or identically patterned on the other. A domino can be stacked on top of another, or it can be laid flat, with the pips touching to form a chain. In the latter case, the first domino to fall is called an “opening double,” and the player calls out the heaviest domino in his or her hand, such as “double-six.” If there is no opening double, players take turns picking dominoes from the stock until someone plays a match.
The most common set of dominoes, which is used in most domino games, contains 28 tiles. These are arranged in a pile, sometimes called the boneyard or stock, with each player picking seven for play. The first player begins by playing a domino; it must have an end that matches the number of pips on the end of the preceding domino (e.g., 5 to 1). Each player then places his or her next domino edge-to-edge against the first, placing it so that its two matching ends are adjacent.
In some games, the pips on the end of a domino are added or subtracted for scoring purposes; in others, the pips have no significance other than to distinguish the individual pieces. A pair of matching dominoes belongs to a suit, which is one of four categories (zero, three, five, and six). The heaviest domino in a suit has the most pips.
Most domino games involve either blocking a competitor or scoring points. Players can also play layout games, in which they attempt to empty their hands before their opponents. Dominoes can be used to construct a variety of structures, such as lines that draw pictures when they fall, or 3D towers and pyramids.
When a domino is stood upright, it has potential energy, or stored energy based on its position. As it falls, this energy is converted into kinetic energy, or the energy of motion, which allows other dominoes to fall in turn. This is what gives rise to the phrase, “the domino effect,” which describes a series of events that begin with a small action and lead to much larger-and often catastrophic-consequences.
Stephen Morris, a University of Toronto physicist, has studied the power of dominoes, and has found that they can actually knock over objects one-and-a-half times their size. His video demonstration shows how this works. The principle is essentially the same as for other types of chain reactions: When one item tips over, it causes other items to tip over as well, and so on. The principle is so powerful that some people use it to make chain reactions of dominoes for fun. This is often done with large sets of dominoes, and some impressive structures can be built. Some even feature themes or messages, such as the Ten Commandments or a Christmas tree.