Vincent Bertin
INPHYNI (Institut de Physique de Nice)
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The physics of pencil drawing
Pencil drawing is one of the oldest forms of human expression. At its core, drawing consists of rubbing a brittle material against a rough surface, leaving behind a permanent trace. Despite its apparent simplicity, this everyday process involves complex contact and fracture mechanics. The resulting pattern depends on multiple factors such as paper texture, pencil hardness, applied load, and stroke speed, which artists intuitively exploit to create distinct textures and shades.
At the microscopic level, graphite does not uniformly cover the surface; tiny flakes are torn off by cellulose fibers, resulting in sparse, heterogeneous deposition. Changing the substrate—e.g., using smoother or rougher paper, engraved or corroded glass—dramatically alters the size, shape, and density of graphite debris. These observations raise fundamental questions: How do surface roughness, applied load, and lead hardness determine wear rate, debris morphology, and the visual shade of the drawing?
To investigate these processes quantitatively, we design an automatic drawing machine inspired by 3D printing technology. This setup allows controlled drawing on diverse surfaces while monitoring wear and trace morphology. Our approach links micro-scale mechanics to macro-scale artistic patterns, revealing a rich interplay between physics, materials science, and tribology.
