Much to the consternation of adults,
a broken mercury thermometer is a
source of delight to a curious child
absorbed by the spectacle of the silvery beads
that elude capture. The epithet ‘quicksilver’
aptly describes the droplets, which seem to
roll rapidly on the surface much like a solid
marble.This unusual behaviour elicits a host
of questions that are relevant to scientists in
diverse fields: from chemists and engineers
interested in the dynamics of drops, to
astronomers interested in the stability of
rotating stars and planets. How and when
can liquid droplets actually roll on a surface?
How fast can they move? Can they be
controlled? And to what end?