A falling domino releases enough stored energy to tip over another domino about 50% larger than itself. Dr. Stephen W. Morris of the University of Toronto illustrates this by using a 5 millimeter high domino to knock over a 1 meter high domino.
There are 13 dominoes in Dr. Morris's line. If he had 29 dominoes, the last one would be as tall as the Empire State Building.
-via The Presurfer | Morris's Website