From Richard Brown, Huntly, Aberdeenshire, UK
Alex Wilkins reports that a slight curve on the surface of a rock helps it make the biggest splash. I am of a generation that received corporal punishment. It was well known that the more charitable disciplinarians used an absolutely flat instrument. We, the recipients, could feel the reason suggested in the research: the flat surface formed an air cushion at the point of impact. By contrast, even slight curvature of the impact surface transmitted much more force (10 August, p 18).
