A domino is a small, thumb-sized rectangular block with one or more faces bearing a pattern of dots or “pips”: 28 such pieces form a complete set. Dominoes can be used for a number of games. Most are played by laying them down in straight or curved lines, or angular patterns. Some of them can even be arranged to form 3D structures such as towers or pyramids.
The earliest recorded uses of dominoes in the West date to the mid-18th century. During this period, the games were most popular in Italy and France. Some of the earliest domino sets were made from wood, such as ebony or ivory; others were cast in metal; and a few were composed of other natural materials. More recently, the pips of dominoes have been replaced with numbers on the ends, making it easier to identify them and to match them together to play a game.
Many people use dominoes to practice a skill or develop a hobby. For example, some people practice the art of domino art, in which they create decorative displays of stacked dominoes that make shapes such as hearts or flowers. People also often enjoy using them as a tool for relaxation or stress relief.
Some of the most popular types of dominoes are designed to be a challenge for players to complete. They may require a large number of dominoes to be laid down to achieve a specified goal, such as covering a large area with them. The challenge can also be a matter of skill, such as the ability to see the entire display before starting or the ability to knock down all the dominoes on a given turn.
Other games of domino involve placing dominoes edge to edge in a line so that the adjacent sides either match or add up to a particular total. These games are often played with a partner or with multiple opponents. They can be competitive or non-competitive, and may have various scoring mechanisms.
Another type of game of domino involves putting one domino into position so that it can be pushed over by another, thus causing the second domino to fall and completing a sequence. This is sometimes known as a chain reaction, and it can be used to make domino chains of impressive size.
Dominoes are much more powerful than we might think. In a 1983 experiment, University of British Columbia physicist Lorne Whitehead showed that a single domino, when properly placed, can actually knock down objects about one-and-a-half times its own size. He set up 13 dominoes—the first one was only 5 millimeters tall and 1 mm thick—and used them to knock down objects that were more than three feet tall.
When you push on a domino, the friction between it and the other tiles causes energy to build up inside of the piece. When the first domino falls, that energy releases and can push on other dominoes. These dominoes, in turn, can move other objects that are far larger than the original domino.