Research in 2016, by scholar Professor Ian Hutchings , University of Cambridge revealed that scribbles in Leonarda Da Vinci ‘s notes  in the  Codex Forster III( Image is shown below) were in fact experiments to determine the laws of frictions. The experiment was about a pulley and weight system, to understand the direct effect of the weight of a block to the amount of friction involved that even students perform today to understand friction. Even though Leonardo Da Vinci has been credited with being the pioneer of Tribology, this particular page marked the beginning of his understanding of this field. 

Sources:

“Study reveals Leonardo da Vincis "irrelevant" scribbles mark the spot where he first recorded the laws of friction.” University of Cambridge, 21 July 2016, www.cam.ac.uk/research/news/study-reveals-leonardo-da-vincis-irrelevant-scribbles-mark-the-spot-where-he-first-recorded-the-laws.

Image Courtesy: Codex Forster III folio 72r Credit: V&A Museum, London