Never assume that Leonardo Da Vinci's doodles are meaningless. That, at least, is the takeaway of a new study out of the University of Cambridge, which shows that a page of Leonardo's scribbled notes from 1493—previously dismissed as "irrelevant" by art historians—is actually the first written demonstration of the laws of friction. It is widely recognized that Leonardo had an exceptional grasp of friction centuries before the modern science of "tribology" was codified. In his mock-ups of complex machines, the Renaissance inventor incorporated friction into the behavior of wheels, axels, and pulleys, recognizing its role in limiting operation and efficiency. But exactly when and how Leonardo first developed his ideas on friction has been a mystery. Now, a detailed chronology put together by Cambridge manufacturing engineering professor Ian Hutchings pegs Leonardo's eureka moment to a tiny, yellowing scrap of paper inked in 1493. Held in the Victoria and Albert Museum of London, this