Dominoes, a cousin to playing cards, have been used for centuries for a variety of games and tests of skill. They are small rectangular blocks that feature one side with a pattern of dots, or pips, and the other blank or marked with a number. There are many different varieties of domino, but the most popular ones feature a number in each square and two “suits” that correspond to those numbers: for example, threes, fours, fives, sixes and sevens; some also have a suit of blanks, or 0’s. A single domino may belong to both of these suits, and a domino set usually contains tiles of all four.

A domino set is typically arranged in a grid on the table, with each tile touching another either horizontally or vertically to form a row. This is called a “layout.” The most popular layout game is a variant of dominoes called “all fives,” where players take turns placing a single domino, then rapping (or knocking) the table until all the pieces have fallen. The first player to play all of his or her dominoes wins the game.

Other games that can be played with a domino set include “blocking” games, in which one player places a domino in the line of a previous domino, and scoring games, in which each player tries to score points by making combinations of spots or numbers on adjacent dominoes. Dominoes are often used for educational purposes, and children’s education materials often teach counting and basic arithmetic using dominoes.

In the real world, a domino effect occurs when a small trigger causes a series of events that affect related things. For example, if a person decides to change his or her diet and starts eating less fat, this may cause a chain reaction where other foods are reduced as well. The idiom domino effect is also used to describe political situations, such as Communism spreading throughout Indochina.

The physics of dominoes reveals interesting parallels to the way nerve impulses travel in the body. A nerve impulse propagates down a neuron’s axon at a constant rate, losing energy as it goes. It can only stop at the end of the axon, where it is detected by other neurons. Likewise, a domino can only fall at the end of the row it has ascended.

Each time a domino is stood upright, it stores potential energy based on its position. When it falls, most of this energy is converted to kinetic energy in the motion of the falling domino. It also takes energy to reset the ionic distribution in the cell after a nerve impulse has propagated down its axon, just as it takes energy for a domino to fall at the end of its row.