Popcorn to most people, is just a fun food to munch on while watching a movie. But to a couple of French investigators, popcorn is a biomechanical enigma waiting to be explained.
PARIS,
To most people, it may be just a fun food to munch while watching a movie.
But to a couple of French investigators, popcorn is a biomechanical enigma waiting to be explained.
In
an unusual study published on Wednesday, engineers Emmanuel Virot and
Alexandre Ponomarenko carried out experiments into what makes popcorn,
well, pop.
Cameras recording at 2,900 frames per second helped show what happened when a kernel of corn strutted its stuff.
When
the temperature reached 100 degrees Celsius (180 degrees Fahrenheit),
some of the moisture inside the corn started to turn into steam, the
researchers found.
As the temperature rose to around 180 C (356 F), pressure built to around 10 bar, or 10 times the atmosphere at sea level.
LEAP RESULTS
Unable
to withstand the stress, the outer shell broke open, causing a dramatic
drop in pressure that forced the kernel's starchy innards to expand and
protrude.
"We found that the
critical temperature is about 180 C (356 F), regardless of the size or
shape of the grain," said Virot, an aeronautical engineer at the elite
Ecole Polytechnique.
The first thing
to emerge from the fractured shell is a limb-shaped structure — a "leg" —
that comes into contact with the surface of the pan and starts to
compress under the heat.
Tensed and
then released, the "leg" causes the corn to leap up — a height ranging
from a few millimetres to centimetres (tenths of an inch to several
inches)-- and emit a "pop" from the sudden release of water vapour.
A few milliseconds later, the granules spewing from inside expand to form a spongey flake.
Evolution from fracture to flake takes less than 90 milliseconds — 0.09 of a second.
The
popcorn's leap results from an intriguing combination of thermodynamics
and fracture mechanics, rather than just the blast of pent-up gases.
"A
piece of popcorn has a singular way of jumping, midway between
explosive plants such as impatiens, and muscle-based animals such as
human beings," the researchers said.
The study appears in a British journal, the Royal Society Interface.
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