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“A domino can knock over another domino about 1.5x larger than itself. A chain of dominos of increasing size makes a kind of mechanical chain reaction that starts with a tiny push and knocks down an impressively large domino.
See http://arxiv.org/abs/physics/0401018 for a sophisticated discussion of the physics.”

First presented by Lorne Whitehead, American Journal of Physics, Vol. 51, page 182 (1983). – pdf