Beyond Quality and Quantity: Contact Distribution Encodes Frictional Strength*

The quantity of real contact between two bodies is classically considered a proxy for frictional resistance. It has been shown more recently that bond density between the two bodes, often called quality of contact, is also a highly relevant factor. Contemporary debate therefore often revolves around the relative importance of these two factors, often completely ignoring the distribution of contact. In this work we take static friction measurements and image the contact plane, then use the contact distribution to predict static friction 5 to 20 times better than existing benchmarks (e.g. total area of contact). Our model has no access to quality of contact, and we therefore conclude that a large portion of the interfacial state is encoded in the spatial distribution of contact, rather than its quality or quantity.