Cornstarch Experiment (Oobleck)
Grade Level: 5
Strand: Understanding Matter and Energy
Topic: Properties of and Changes in Matter
Specific Expectation:
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Use scientific inquiry/experimentation skills to investigate changes of state
and changes of matter (2.3)
Identify properties of solids, liquids and gases (e.g. solids have definite
volume and hold their shape; liquids have definite volume but take the
shape of their container or spread when they are not contained; gases have
no definite volume and take the volume and shape of their container or
spread when they are not contained), and state example of each.
Materials needed:
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1 cup cornstarch
Bowl
About ½ cup of water
Spoon
Medium size container
Food coloring
Ziploc bag
Procedure:
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Pour ¼ of the box of cornstarch into the mixing bowl
Slowly add about ½ a cup of water and stir
Continue adding in small amounts until reaching a pancake batter
consistency
Add a few drops of food colouring
Scientific Principle:
Oobleck is an interesting substance which has generated extensive literature
attempting to explain its unusual properties. When little pressure is applied to the
mixture, it flows like a liquid. A spoon or your finger can easily be pushed to the
bottom of a cup of the mixture if you do it slowly. However, when you apply
increased pressure Oobleck (the mixture) begins to act like a solid and it will keep
its shape and resist movement making stirring the substance impossible. Since
Oobleck does not follow the rules of most liquids, it is called a non-Newtonian
fluid.
So, what makes Oobleck act like both a liquid and a solid? Imagine that you can
see the individual molecules of cornstarch and water and think about how they
might act when being poured or pushed and pulled.
The cornstarch and water mixture will act like a solid sometimes and a liquid at
other times. This mixture is an example of suspension. Where particle stay undissolved in a liquid, the cornstarch molecules are dispersed into the water. If the
cornstarch mixture is pinched, it causes the long starch molecules to go closer
together. The impact of the force traps the water between the starch molecules to
form a solid structure. When you release the pressure of your fingers the
cornstarch will be able to flow again. Viscosity is the resistance for a liquid to
flow. For example honey has a high resistance to flow and water has a low
resistance to flow. Therefore, when you pour honey it moves very slowly but
when you pour water it moves quickly.
Scientists have formulated several different possible models attempting to explain
the unusual behavior of Oobleck however there is no conclusive explanation of
why Oobleck behaves as it does. As you can clearly see it is very difficult to
observe what is going on at a molecular level just by observing the properties of a
substance.
Sources: www.guam.net/planet/oobleck.html and www.stevespanglerscience.com
Michela Chirico and Lorraine Noel-McVey
BACKGROUND INFORMATION
Gases, Liquids, and Solids
Gases, liquids and solids are all made up of atoms, molecules, and/or ions, but the
behaviors of these particles differ in the three phases. The following chart
illustrates the characteristics of gases, liquids and solids.
Some Characteristics of Gases, Liquids and Solids and the
Microscopic Explanation for the Behavior
gas
liquid
solid
assumes the shape and
volume of its container
particles can move
past one another
assumes the shape of
the part of the
container which it
occupies
particles can
move/slide past one
another
retains a fixed volume
and shape
rigid - particles locked
into place
compressible
lots of free space
between particles
not easily
compressible
little free space
between particles
not easily
compressible
little free space
between particles
flows easily
particles can move
past one another
flows easily
particles can
move/slide past one
another
does not flow easily
rigid - particles cannot
move/slide past one
another
Source: www.chem.purdue.edu/gchelp/atoms/states.html