  We explore the hypothesis that, due to small van der Waals forces between
constituent grains, small rubble pile asteroids have a small but non-zero
cohesive strength. The nature of this model predicts that the cohesive strength
should be constant independent of asteroid size, which creates a scale
dependence with relative strength increasing as size decreases. This model
counters classical theory that rubble pile asteroids should behave as
scale-independent cohesionless collections of rocks. We explore a simple model
for asteroid strength that is based on these weak forces, validate it through
granular mechanics simulations and comparisons with properties of lunar
regolith, and then explore its implications and ability to explain and predict
observed properties of small asteroids in the NEA and Main Belt populations,
and in particular of asteroid 2008 TC3. One conclusion is that the population
of rapidly rotating asteroids could consist of both distributions of smaller
grains (i.e., rubble piles) and of monolithic boulders.
