As the distance between the dominoes is increased, the speed of their toppling decreases.
Domino effect normally refers to how an action causes a similar action to occur This second reaction will trigger the next reaction and this will continue in a sequence until the last possible action has been triggered.
The simplest demonstration of this is by arranging domino tiles in a row. When the first tile is tripped, it will topple over and collide with the next tile in front of it. This will go on until the last tile has been knocked down.
No matter how long the chain of dominoes, if they are properly arranged in the first place, they will continue to topple from tile to tile, as long as the distance between the tiles is shorter than their height. Potential energy is stored in the tiles when they are made to stand upright. The energy required to topple the next domino is less than the energy involved in the collision of the tiles. The makes the entire domino effect self sustaining.