Figure 5: Hard and soft contacts.
(a) When the contact radius is much larger than Υsv/E, the contact is described by the JKR theory, which balances adhesion and elastic stresses (blue arrows). The surface tension contribution is negligible. (b) When the contact radius is much smaller than Υsv/E, surface tension governs contact mechanics and adhesion mimics adsorption on a fluid interface. The undeformed solid surface hits the particle at a fixed contact angle given by the generalized Young’s law in equation 3. Elastic forces are negligible.
