JKR theory (Johnson-Kendall-Roberts, 1971): adhesion enlarges the Hertzian contact area by a factor due to surface energy. Contact radius a³ = (R/E*)·[F + 3πWR + √(6πWRF + (3πWR)²)]. The pull-off force is F_pull = −(3/2)πWR — independent of elastic modulus! This differs from the DMT model which gives F_pull = −2πWR. JKR applies to soft, large, high-adhesion contacts (large Tabor parameter μ = (RW²/E*²z₀³)^(1/3)).