A domino is a small rectangular wood or plastic block, each face of which is either blank or marked with dots resembling those on dice. Dominoes are normally twice as long as they are wide. The most common set of dominoes has 28 tiles, but extended sets can be obtained with more tiles. Dominoes are normally stacked on end in long lines, and when the first domino is knocked over it triggers a chain reaction that causes all the others to topple over. Dominoes have become popular toys for children and can be used to create elaborate designs. They can also be used to play games that involve blocking or scoring.

A professional domino artist, who goes by the name Hevesh, works with thousands of dominoes to create dazzling displays. Hevesh uses a number of physical principles to help her design these massive sets, but one phenomenon is particularly important: gravity. “When a domino is standing upright, it has potential energy, or stored energy based on its position,” says physicist Stephen Morris. “When it falls, much of this potential energy is converted into kinetic energy, or energy of motion, and that can then push on the next domino in line.”

Hevesh takes special care to make sure each part of her designs will work. She often tests out each section before putting them together, and she films her tests in slow motion to catch any errors. This method allows her to correct the sections that don’t work and create more perfect arrangements. She’s worked on projects that use as many as 300,000 dominoes, and she helped break the Guinness World Record for the most dominoes toppled in a circular arrangement. Even the biggest domino installations can take several nail-biting minutes to fall, however.

Dominoes can be played on a table or other flat surface, but they are most often laid out on the floor in a line. Each player in turn places a domino onto the line, positioning it so that the matching ends of the tile touch each other. A domino must have a single number showing on both of its sides or be blank, and additional tiles may only be placed on the end of a double. The shape of a domino chain develops into a snake-line as additional tiles are added to the layout.

Dominoes are usually grouped into suits, with each suit consisting of different numbers of tiles. The most common suit is the suit of double six, but larger sets exist that increase the maximum number of spots on each end from six to twelve or even twenty-three. Larger sets are also available with more readable Arabic numerals, which can be helpful for players who cannot easily distinguish the pips on a domino. In general, the longer a domino set is, the more difficult it is to read the number of pips on each end.