Set a steel bar on its bearing and the two of them touch, obviously. Now fall toward the contact until a fingernail's width fills the horizon. The surfaces are mountain ranges, and they lean on each other at a few dozen glowing peaks. Everything you call friction, and everything you call wear, happens up there.
Press the ranges together harder and more peaks join in, but the arithmetic never gets close to even: the area actually carrying the load stays a few thousandths of the area you can see.
One peak carries a millionth of the bar's weight, which at its scale is a mountain of pressure: gigapascals, enough to weld it to the peak across the street. Slide, and the weld must shear. The peak survives, hardens, and does it again. It has done this a thousand times this week.
Each pass is the same little drama: touch, weld, shear, let go. And each pass leaves the peak a little harder than it was, until hardening runs out of room.
Pass one thousand and one asked more than the weld could give. The peak tore free and became a third body: work-hardened, oxide-crusted, harder now than either surface that made it, tumbling between them and plowing a groove it will never have to pay for.
A wear particle is a career change. Born as part of the surface, it comes back as an abrasive: dragged through its birthplace, displacing ridges to either side, picking up mass as it goes.
Nothing dramatic ever happened to bar A. It just went to work every day between a bearing and a load, and the mountains slowly emigrated. Wear is not an event. It is a bookkeeping of departures, and Archard's rule is the exchange rate.
The ledger itself is one line long: volume lost grows with load and sliding distance, and shrinks with hardness. Everything a coating or a heat treatment buys you is a smaller exchange rate.
Fracture is loud, and rare. Wear is quiet, and it is happening right now to every machine you own, at the tops of mountains you will never see, one departed monolayer at a time.
Fracture is a moment.
Wear is a career.
I audit the mountains.