Size matters in the way materials behave. An introductory PowerPoint and an activity write-up. Three activities illustrate how the surface to volume ratio changes as the size changes. In the first, a deck of playing cards is used to make square arrays of cards of increasing size. Next wooden cubes are used to make similar observations in 3 dimensions. Finally, comparing the rates at which an intact Alka Seltzer tablet and a crushed tablet react in water shows the effect of particle size on chemical reactions.