Water, Sewage & Effluent November December 2018 | Page 27

Waves and siphons
Waves (powered by wind), tides
(primarily affected by the moon’s
gravitational forces), and tsunamis
(often triggered by earthquakes
and underwater landslides or
volcanoes) can cause water to go
against gravity. The energy and
forces produced by these natural
phenomena can push water
upward, allowing it to rise naturally
into a wave or run up a shoreline.
A siphon acts under different
pressures. People have used siphons
since ancient times; the ancient
Egyptians used siphons for irrigation
and winemaking. But there is still
debate about how siphons work.
You can visualise a siphon by
thinking of two cups connected by
a tube shaped like an upside-down
‘U’. The water-filled cup sits on a
stair, and an empty cup sits below
it. If an experimenter puts one end
of the tube into the water-filled cup
and sucks the air out of it as you
would when using a straw, that will
allow the water to flow into the tube.
A siphon is created once the water
flows up one side of the tube and
down the other, into the empty cup.
What is interesting is that siphons
also work in vacuums, so it does not
appear that atmospheric pressure
is at play. Rather, gravity and
molecular cohesion appear to be
involved, according to a 2015 study
in the Journal of Scientific Reports.
Gravity accelerates the water
through the ‘down’ part of the tube,
into the lower cup. And, because
water has strong cohesive bonds,
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these water molecules can pull
the water behind them through the
uphill portion of the tube. However,
many liquids that do not have
strong cohesive bonds still work in
siphons, so it is unclear exactly how
siphons work in different cases.
Capillary action
What about the paper towel example?
This action, called capillary action,
allows small volumes of water to
flow uphill, against gravity, so long
as the water flows through narrow
and small spaces.
This upward flow happens when
a liquid’s adhesion to the walls
of a material, such as the paper
towel, is stronger than the cohesive
forces between its liquid molecules.
An example is in plants: water
molecules are drawn up capillaries
called the xylem, helping the plant
to draw in water from the soil.
Other uphill-flow
instances in nature
There are other instances in
nature in which water has run
uphill naturally. For example, an
8.0-magnitude earthquake shook
south-eastern Missouri so hard that
the Mississippi River temporarily
flowed backwards.
And then there’s the Leidenfrost
effect. Have you ever noticed whilst
cooking that sometimes bead-
like water droplets seem to dance
around the bottom of the hot pan?
Well, it only occurs above specific
temperatures. If you place a liquid
onto a hot surface that is below
the boiling point of the liquid (100
degrees Celsius for water), the
liquid will bubble away and slowly
evaporate. And if you increase the
temperature to slightly above the
boiling point, the liquid evaporates
rapidly. However, if you increase
the temperature even more,
exceeding the Leidenfrost point,
then the Leidenfrost effect comes
into play. This occurs when the
surface temperature is so hot that it
generates a thin layer of vapour that
lies between the surface itself and
the liquid. This causes the liquid to
T
he answer is yes, if the
parameters are right. For
instance, a wave on a beach
can flow uphill, even if it is for just a
moment. Water in a siphon can flow
uphill too, as can a puddle of water
if it is moving up a dry paper towel
dipped in it.
But even more curiously is that
Antarctica has a river that flows
uphill underneath one of its ice
sheets. So, how does science
explain these upward watery
movements?
become insulated, and ‘climb’ tiny
stairs made of vapour.
The river in Antarctica
that flows uphill
Recently, it has been discovered
that there is a river that flows
uphill beneath one of Antarctica’s
ice sheets — according to a
geophysics professor, Robin Bell,
at Columbia University’s Lamont-
Doherty Earth Observatory in
New York. The location is in the
Gamburtsev Mountains (also known
as the Gamburtsev Subglacial
Mountains
—
a
subglacial
mountain range located in East
Antarctica, just underneath the lofty
Dome A, near the Southern Pole of
Inaccessibility.)
“In the valleys, there is water,
and we can tell because when we
fly over it, the echo from the ice-
penetrating radar is much stronger.”
Intriguingly, the researchers
came to the conclusion that the
river is flowing backwards because
the ice on top of it is aligned against
the direction of the ice flow. This
alignment, and the enormous
pressure from the ice sheet above
it, push the water uphill, Bell said.
“We realised that the ice is forcing
the water up the hill, squeezing the
water backwards,” said Bell.
The
subglacial
rivers
of
Antarctica appear to be an active
area of research — and an area
of scientific debate. There are
scientists who argue that gravity
is less dominant in determining the
direction of flow, since the pressure
of the ice takes over.
So, something to think about
is this: Science states that if you
measure the place where water
started versus where the water
ends, the start level must be higher
than the ending level, because all
of the water’s kinetic energy comes
from gravitational potential energy.
Anything else would defy the laws
of physics. Then, I suppose, I would
ask you this: Does the uphill-flowing
Antarctic subglacial river then not
defy the laws of physics? u
Source: livescience.com
Water Sewage & Effluent November/December 2018
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