From a
physics standpoint, what is going on when popcorn
pops?
Why
do corn kernels pop? In order to find the answer we need
to look at the process of how popcorn kernels are
produced. Certain types of corn are grown and when they
are mature enough, harvested. When harvested, the moisture
content of the kernels is around 16%-20% (“From Seed to
Snack”). The whole ears of corn are then stored for up to
twelve months until the kernel moisture content is
somewhere around 14%. The kernels are then stripped from
the cob and ready for use.
Now
that
we know more information about popcorn kernels after they
have been processed we can figure out how they pop. We
know that when water is heated up it expands and becomes
steam and that there is water inside a popcorn kernel, so
a good assumption would be that the water inside a popcorn
kernel begins to boil; producing steam and increasing the
pressure, and at some point the kernel cannot take the
force of the steam anymore and ruptures. This is in fact
the situation. The popcorn kernel for our discussion can
be assumed to be a perfect sphere with a radius of 0.5 cm
with moisture trapped inside. As heat is inputted into the
kernel the temperature begins to raise and the water
inside begins to increase in temperature as well. When the
pressure inside is greater than the kernel can withstand,
it bursts. A slow motion demonstration of a popcorn kernel
popping is shown on the right. The pressure present in a
popcorn kernel the moment before it pops is about 130 psi
(pounds per square inch). To gain a little more insight a
brief calculation of how much force is inside the kernel
will be performed. We know pressure equals force over
area, P = F/A (Knight,
410). We also know that P = 130 psi and the surface area
of a sphere is SA = 4*π*r^2 and the radius is 0.5 cm.
Converting the radius to inches, plugging in those
formulas into the equation, and rearranging you get:
Source:
http://giphy.com/gifs/popcorn-popping-mi6KzW76uXqU0
