- Friction has long been said to come in two forms – static and dynamic. Two bodies held together by static friction do not move at all until the force shearing them apart passes a critical value.
- Our experiments show that this view is true only if one does not examine static friction with sufficient care. Our samples of ceramics on steel slide in reproducible ways – if only by nanometers – no matter how small the shearing forces.
- The results can be explained by modifications of theories originally created to study the dynamic sliding of rock over rock. The same equations show that there should always be a little sliding even when forces are much smaller than the limit of static friction, and are in accord with experiments.
