The fall of a drop into a cup of coffee and the consequent process is a
remarkable event. After the drop touches the surface of the liquid, a fight of
gravity, surface tension, inertia and viscosity starts and results in what we
see in the pictures. The drops were falling from about 25 centimeters height
and triggered a photo gate connected to a photographic flash. The flash fired
with a tunable delay which enabled us to capture different phases of the
process. The tearing of the liquid column into individual drops is an
especially interesting moment. Note also that the shape of the drops is
spherical due to the surface tension and not the one usually shown in children
books. The last picture shows collision of a secondary drop with a fast primary
drop that is just coming down. We used an ordinary camera Nikon D50
to take all the photos.
You can also see a short video (formate Quick Time 6, 56kbps) composed of the
photos.