Dominoes are rectangular pieces of wood, bone, ivory, plastic, or resin with a line down the middle to divide them visually into two squares. Each square is marked with an arrangement of spots, or pips, like those on a die. The dominoes with pips on one side are referred to as “pipless,” and those with a number of pips on the other side are called “dominoes with numbers.”
When a domino is laid down, it becomes the beginning of a chain reaction that continues until the entire set has fallen. The speed at which the dominoes fall is determined by the energy stored in each one. Dominoes that are pushed together release their energy slowly and steadily as they tumble down the row. It can take several nail-biting minutes to watch a huge row of dominoes fall.
The number of pips on the two sides of a domino determines its value. The most common dominoes have six pips on both ends, but some are doubles that have only four pips on one side and blanks on the other. Depending on the game being played, each domino is assigned a rank or weight that ranges from a maximum value of six pips to none or blank. The number of pips on a domino also determines the amount of force required to knock it over.
A domino can be matched to a single domino only when the number of pips on the matching side is equal to or greater than the number of pips on the domino that was last played. When this occurs, the new domino is placed on top of it. Each player then draws a hand of tiles according to the rules of the game being played, and places them in front of him.
After a player has drawn his hand, he begins play by placing a domino in the line of play, or string, that is being formed. The open end of the domino must match the previous tile played, and it is then counted as part of the total line of play in the game. The total is determined by counting the number of pips on both ends of the previous domino.
Usually, each player takes a turn to place a domino in the line of play. However, if the player holding the heaviest double is not able to play it, or if a game has been blocked (everyone is unable to make another play), then the winner of the last game may begin.
Some players build massive chains of hundreds or even thousands of dominoes that form pictures, walls, and 3-D structures like towers and pyramids. These are often shown at events, where builders compete to create the most imaginative domino effect or reaction before a live audience. These amazing displays can take hours or even days to fall, and it isn’t unusual for each domino to require a small nudge from the hand of only one person before it falls.