Dominoes falling make a wave. We may conjecture that the wave speed v depends on the spacing d between the dominoes, the height h of each domino, and the acceleration due to gravity g.
(a) Find the dimensional formula for each of the four quantities.
(b) Show that {∏1 = h/d, ∏2 = dg/v2 g is a complete set of dimensionless products. 

(c) Show that if h/d is fixed then the propagation speed is proportional to the square root of d.