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.

hlsfrf4wo8oqduw3exkiNow, 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 notebook page was actually a subject of academic debate years ago, because of the faint sketch of an old woman near the top, followed by the statement “cosa bella mortal passa e non dura,” which translates to “mortal beauty passes and does not last.” But the sketches beneath these ominous words were dismissed by the 1920s museum director as “irrelevant notes and diagrams in red chalk.”

As Hutchings explains in his paper, those red scribblings are actually a pivotal moment in the history of tribology. They show blocks being pulled by a weight hanging over a pulley—the very same sort of experiment used in introductory physics today to demonstrate how friction works. The paper goes on to trace Leonardo’s 20-year study of friction from this initial incarnation to more complex demonstrations and ideas.

“The sketches and text show Leonardo understood the fundamentals of friction in 1493,” Hutchings said in a statement. “He knew that the force of friction acting between two sliding surfaces is proportional to the load pressing the surfaces together and that friction is independent of the apparent area of contact between the two surfaces. These are the ‘laws of friction’ that we nowadays usually credit to a French scientist, Guillaume Amontons, working two hundred years later.”

I think the real takeaway here is that we should encourage scientists and engineers to pore over all of Leonardo’s old notes. Who knows what other incredible insights were just… overlooked?