Quicksand Cornstarch Suspension
Anyone who has ever watched a classic western movie knows about
the dangers of quicksand. You know… that gooey stuff that grabs a
hold of its victim and swallows them alive! So, what is quicksand and
how does it really work? In this experiment, you'll learn how to mix up
a batch of thick, gooey material that behaves just like real quicksand.
In this experiment, you’ll be using ordinary cornstarch to model the
behavior of real quicksand and learn about the properties of this non-
Newtonian mixture.
IMPORTANT - READ THIS! Ironically, the cornstarch will not stay mixed
with the water indefinitely. Over time, the grains of cornstarch will
separate from the water and form a solid clump at the bottom of the
plastic storage bag. It is for this reason that you must not pour this
mixture down the drain. It will clog the pipes and stop up the drain.
Pour the mixture into a zipper-lock bag and dispose of it in the
garbage.
Materials
•One box of cornstarch (16 oz.)
•Large mixing bowl
•Cookie sheet, square cake pan, or something similar
•Pitcher of water
•Spoon
•Gallon size zipper-lock bag
•Newspaper or a plastic drip cloth to cover the floor
•Water
•Food Coloring
Experiment
1. Pour approximately 1/4 of the box (about 4 oz.) of cornstarch into the
mixing bowl and slowly add about a half a cup of water. Stir.
Sometimes it is easier to mix the cornstarch and water with your bare
hands (of course, this only adds to the fun).
2. Continue adding cornstarch and water in small amounts until you
get a mixture that has the consistency of honey. It may take a little
work to get the consistency just right, but you will eventually end up
mixing one box of cornstarch with roughly 1 to 2 cups of water. Notice
that the mixture gets thicker or more viscous as you add more
cornstarch.
3. Sink your hand into the bowl of “quicksand” and notice its unusual
consistency. Compare what it feels like to move your hand around
slowly and then very fast. You can’t move your hand around very fast!
In fact, the faster you thrash around, the more like a SOLID the gooey
stuff becomes. Sink you entire hand into the goo and try to grab the
fluid and pull it up. That’s the sensation of sinking in quicksand!
4. Drop a plastic toy animal into the cornstarch mixture and then try to
get it out. It’s pretty tough even for an experienced quicksand
mixologist.
Slap Test Pour the mixture onto the cookie sheet or cake pan. Notice
its unusual consistency when you are pouring it into the pan. Stir it
around with your finger, first slowly and then as fast as you can. Skim
you finger across the top of the glop. What do you notice? Sink you
entire hand into the glop and try to grab the fluid and pull it up. That’s
the sensation of sinking in quicksand!
Try to roll the fluid between your palms to make a ball. You can even
hold your hand flat over the top of the pan and slap the liquid glop as
hard as you can. Most people will run for cover as you get ready to
slap the liquid, fearing that it will splash everywhere.
According to theory, the mixture should stay in the pan. Yeah, right! If
your cornstarch water mixture inadvertently splatters everywhere, you
will know to add more cornstarch. When you are finished, pour the
glop into a large zipper-lock plastic bag for later use.
How does it work?
The cornstarch and water mixture acts like a solid sometimes, and a
liquid at other times? Actually, this concoction is an example of a
suspension - a mixture of two substances, one of which is finely
divided and dispersed in the other. In the case of the cornstarch
quicksand, it's a solid dispersed in a liquid.
When you punch the cornstarch quicksand, you are forcing the long
starch molecules closer together. The impact of this force traps the
water between the starch chains to form a semi-rigid structure. When
the pressure is released, the cornstarch flows again.
All fluids have a property known as viscosity - the measurable
thickness or resistance to flow in a fluid. Honey and ketchup are
liquids that have a high resistance to flow. Water has a low viscosity.
Newton said that viscosity is a function of temperature. So, if you heat
honey, the viscosity is less than that of cold honey. The cornstarch
and water mixture and quicksand are both examples of non-
Newtonian fluids because their viscosity changes when stress or a
force is applied.
What is Quicksand? Quicksand is nothing more than a soupy mixture
of sand and water, where the sand is literally floating on water.
Scientifically speaking, quicksand is actually a substance that
behaves like both a solid and a liquid at the same time. This is the
interesting sensation you experienced with the cornstarch and water
mixture. Quicksand is just solid ground that has been liquefied by too
much water, and the term "quick" refers to how easily the sand shifts
when in this solid-liquid state.
Quicksand is created when water floods or saturates an area of loose
sand and the sand is begins to move around. Think of quicksand as a
soupy mixture of sand and water that is constantly being stirred. When
the water in the sandy soil cannot escape, it creates a liquid-like soil
that can no longer support any weight. If an excessive amount of water
flows through the sand, it forces the sand particles apart. This
separation of particles causes the ground to loosen, and any weight
on the sand will begin to sink through it.
The quicksand phenomenon can be caused by an uprising of water
from something like flowing underground water or even an
earthquake where the sand is agitated. You are likely to find
quicksand around riverbanks, lake shorelines, marshes, beaches,
near underground springs or any place where an uprising of water
over saturates and agitates the sand.
The next time you are standing barefoot on the beach, think about the
properties of quicksand. Normally, the grains of wet sand are
compressed together tightly and this firm ground easily supports your
weight. The friction between grains of wet sand is strong enough to
make it easy to build sand castles. However, when the sand on the
beach is flooded with an excess amount of water, the agitated sand
particles begin to move, separate and quickly wash away right from
under your feet!
This activity is a great example of how to use a model to study
something that most of us will never see in person. While the
cornstarch and water mixture is not real quicksand, its behavior is
strikingly similar. The use of these kinds of models are an important
part of a scientist’s research into the areas of the unknown.
Additional Info
Escaping from Quicksand According to The Worst-Case Scenario
Survival Handbook, escaping from quicksand is easier than you might
think. Stepping into quicksand is like stepping in a pond of goo. Your
weight causes you to sink. A person’s natural instinct is to thrash
around in an attempt to get out. In fact, this is the worst thing you could
do because you only succeed in forcing yourself down farther in the
quicksand pit. The best thing to do is to move slowly to bring yourself
to the surface, lie back, and try to float on your back. According to the
experts, you’ll be able to use your arms to slowly paddle to safety
Experiment from: Steve Spangler Science
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