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charon writes:

Scientists can model friction pretty well—after all, it plays a role in everything from manufacturing to biomechanics—but the model used, known as the "rate-and-state friction model" (or "RSF" for short), is not based on a fundamental understanding of friction. Instead, the RSF model is based on experiments and observations. The model has a good track record of fitting data already measured, but the best, most trustworthy models are those based on fundamental physics that not only are a great match to experimental results and observations, but that can actually predict friction without needing any information or measurements ahead of time.

In research just published in the American Physical Society's journal Physical Review Letters, a team of researchers led by scientists at the University of Pennsylvania provide new insight into friction at the nanoscale. Their work will help establish a better physical basis for models of the static friction that develops between the surfaces of rocks, like what we see prior to earthquakes, and of other materials.

Imagine two jagged edges trying to slide past one another, as in the case of tectonic plates. At some point, the kinetic friction (the friction between two moving surfaces) becomes so strong that they stop moving. In rocks and many other materials, this leads to something called frictional aging. Frictional aging means that the static friction (the force required to get two stationary surfaces moving) changes with time: it increases dramatically at first, and then continues to grow more slowly.

Kaiwen Tian et al. Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale Physical Review Letters 118. DOI: 10.1103/PhysRevLett.118.076103

Original Submission