Nonlinear amplification of adhesion forces in interleaved books.

It is nearly impossible to separate two interleaved phonebooks by pulling their spines. The very slight force exerted by the outer sheets of the assembly is amplified as the exponential of the square of the number of sheets, meaning that even a small number of sheets can create a highly resistant system. We present a systematic and detailed study of the influences of the normal external force and the geometrical parameters of the booklets on the assembly strength. We conclude that the paper-paper adhesion force between the two outer sheets, on the order of a few [Formula: see text],  is the one amplified by the interleaved-book system. The two-phonebook experiment-which has attracted the attention of students and the non-scientific public all around the world as an outstanding demonstration of the strength of friction-appears to also be a spectacular macroscopic manifestation of the microscopic coupling of friction and adhesion.