Cornstarch Experiment (Oobleck) Grade Level: 5 Strand: Understanding Matter and Energy Topic: Properties of and Changes in Matter Specific Expectation: 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: 1 cup cornstarch Bowl About ½ cup of water Spoon Medium size container Food coloring Ziploc bag Procedure: 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
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