  It is nearly impossible to separate two interleaved phonebooks when held by
their spines. A full understanding of this astonishing demonstration of solid
friction in complex assemblies has remained elusive. In this Letter, we report
on experiments with controlled booklets and show that the force required
increases sharply with the number of sheets. A model captures the effect of the
number of sheets, their thickness and the overlapping distance. Furthermore,
the data collapse onto a self-similar master curve with one dimensionless
amplification parameter. In addition to solving a long-standing familiar
enigma, this model system provides a framework with which one can accurately
measure friction forces and coefficients at low loads, and that has relevance
to complex assemblies from the macro to the nanoscale.
