Clutching at straws © stock.adobe.com/au/EvanTravels
The science of spill prevention It doesn’t take a genius to know that if you knock a glass of water on its side, the liquid will spill out. However, if you happened to be drinking your water through a thin straw, some of the liquid will be retained within this straw — even when turned on its side.
On the other hand, if the diameter of the glass
carefully designed, the area of the exposed liquid
ut what is it exactly that makes this
is small enough, such as in a very thin straw, then
surface could change dramatically in response
possible? Is it down to the size of the straw, its shape,
gravity is not able to overcome the forces of surface
to small changes as it crosses the threshold
its material or something else entirely? Seven years
tension and the liquid remains within the tube. This
from staying put to spilling out. Their precise
ago, Professor Andrew Parry, Dr Carlos Rascón and
is why drinking straws, or capillaries in pens, are
calculations could have application in technologies
Professor Dirk Aarts began the calculations that
only a few millimetres across.
that have liquids present at small scales — such
would eventually provide them with the answer.
However, the researchers found that this
as biomedical diagnostics, oil recovery and inkjet
If you look closely at water in a glass, you can
apparently simple rule relating to the size of the
printing — where choosing the right tube shape
see the edges curve up slightly, so that the surface
tube opening breaks down when its cross-section
could be as important as its size.
of the water looks like a shallow bowl. This is due
is changed from being circular to being elliptical or
“We have discovered that it should be possible
to the force of surface tension, a phenomenon
triangular. In this case, it is possible that the liquid
to create minute straw shapes that would mean
that determines how the liquid surface touches the
will spill even when the tube is microscopically
that any liquid spills or empties out of the tube,
sides of the glass. The majority of the liquid in the
no matter how thin it is,” said Professor Parry.
glass is not held this way, so that when the glass is
Writing in the journal Proceedings of the
tipped to the side, the force of gravity wins and all
National Academy of Sciences, the researchers
This article is a modified version of a news item published
the liquid spills out.
propose that if the size and shape of a tube are
by Imperial College London under CC BY 4.0
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