Just What is Oobleck??!! (Teacher’s Guide)
Objective: The students will use process skills of investigation to determine the ratio of water to powder and which mystery powder forms Oobleck. They will then explore Oobleck and attempt to determine whether it is a solid or a liquid.
Materials : 4 boxes of corn starch 1-gallon Ziploc bag of flour 1-gallon Ziploc bag of baking soda 1-gallon Ziploc bag of powdered sugar 1-gallon Ziploc bag of corn starch 1-teaspoon measuring spoon (1 per bag of mystery powder) 3- or 5-oz. Solo cups (2 per group and 1 per student) ¼- or ½-teaspoon measuring spoons or graduated cylinders (1 per group) Food coloring (optional) Popsicle sticks for stirring (optional; 1 per group and 1 per student) Paper towels Water Plastic cups or beakers for the water (1 per group) 2 1-tablespoon measuring spoons Elmer’s Glue-All Borax Snack-size Ziploc plastic bags (2 per student)
How To Make Oobleck: 1. Mix together 3 parts (teaspoons) cornstarch to 1.5 parts (teaspoons) water. 2. Add food coloring, if you’d like. (It’s easiest to add it to the water before mixing it with the cornstarch). 3. When the proper consistency has been reached, the mixture will be difficult to stir. (The 2:1 ratio will result in Oobleck that is slightly runny, but it is of the correct consistency; to make it less messy if students put it in their hands, add maybe another ¼- to ½- teaspoon of cornstarch).
How To Make Glurch: 1. Mix together 10 teaspoons of powdered Borax with 1 quart of water and shake thoroughly (it helps if the water is warm). This solution should be saturated (not all of the Borax should dissolve). 2. Pour 1 tablespoon of Elmer’s Glue-All into a snack-size Ziploc bag. 3. Add 1 tablespoon of the Borax solution. 4. Add some food coloring, if you’d like. 5. Zip the bag shut and begin kneading it to mix the contents; this may take a few minutes. You should begin to feel the contents solidifying; if not, or if only
1 some of the glue and Borax solution have solidified, try adding more of the Borax solution and mixing again. 6. Once the Glurch has been formed, if you add more of the Borax solution to it, it will become more rigid.
Set Up: In advance, prepare a small amount of Oobleck. Have the four 1-gallon Ziploc bags on a central table simply marked as mystery powders (A), (B), (C), & (D). (If you are doing this for more than one class, I would suggest changing the letters on the bags, so that the students from the first class will not be able to tell the students from subsequent classes which of the bags contains the correct powder). Have supplies and measuring devices either at a central station or already at the individual tables. The ideal group size for this activity is four students.
Introduction : Using a small amount of pre-made Oobleck, you could begin by telling the students that when you woke up this morning you found this goo on your front porch as you were getting the paper. Your next-door neighbor had found the same thing on her back patio several days before, and you and she had decided to try to find out what the goo was made of. Using the scientific method, the two of you were able to figure it out, and you thought that the students might have some fun doing the same. You can then mention that you had decided to call the goo “Oobleck” because it reminded you of the green goo that fell out of the sky in the Dr. Seuss book, “Bartholomew and the Oobleck”. You can briefly tell them what the book is about. Explain to the students that their job for the next two days is three-fold: A) To find the proper ratio of water to powder needed to make Oobleck that is of the correct consistency; B) Determine which powder is the Oobleck powder using the previously determined ratio of water to powder mixture; and C) Experiment with Oobleck and determine whether it is a solid or a liquid.
If time permits, they can experiment with Oobleck and Glurch (a polymer that also exhibits some properties of both solids and liquids) to determine how the two substances are similar and how they differ.
Procedure: (Day 1) 1. Follow introduction.
2. Once they have seen what Oobleck should look like, have the students fill out the first worksheet (page 1 of Day 1 of the Oobleck lab).
2 3. Give each group 3 teaspoons of cornstarch (“Oobleck powder”) and allow the group to experiment and discover the ratio of water to powder needed to make Oobleck that is of the correct consistency.
4. Have the groups then explore the other powders to determine which powder is the "Oobleck powder” using the water to powder ratio previously determined from the first experiment.
Procedure: (Day 2) 1. Once the correct powder has been determined, have each student make a small amount of Oobleck and allow them to explore Oobleck for a while. Have students record their observations on the “Data Collection and Analysis” worksheet. They should also answer the questions on pages 1-2.
2. To save class time, the students can fill in the conclusion section of the “Data Collection and Analysis” worksheet and the worksheets on pages 4-5 for homework.
3. At the end of class, distribute small Ziploc sandwich bags for students to take their Oobleck home in. Explain to them that if it dries out, all they have to do is add water!!
4. If the students finish quickly or if you can spare another class period, you could do the activity, “A Competition of Colloidal Proportions!”, in which the students can compare and contrast the properties of two colloids, Oobleck and Glurch, and then answer questions based on their experiments.
Background Information and Terminology :
Oobleck is an interesting substance. When little pressure is applied, it flows like a liquid. A spoon or your finger can easily be pushed to the bottom of a cup of Oobleck if you do it slowly. When more pressure is applied, Oobleck begins to act like a solid. It will keep its shape and resist movement. Stirring Oobleck quickly is impossible. Another fun activity (though potentially messy!) is to pour a little Oobleck in the palm of your hand and watch it puddle like a liquid. Now make a fist and quickly open your hand. The Oobleck will have formed a hard ball from the pressure of your fist; but when the pressure is released, it will seem to "melt" into a liquid again. Since Oobleck doesn’t follow the rules of most liquids, we call it a non- Newtonian fluid. All that means is that it is a liquid that doesn't follow Newton's equations for liquids under pressure. Another example of a non-Newtonian fluid is the glass in very old buildings that is thin at the top and thick at the bottom - it is this way because it is slowly flowing out of the pane. Yet another example is ketchup; have you ever noticed that whacking the bottom of a ketchup bottle doesn’t seem to make the ketchup come out any faster? That’s because when you hit the bottle, you’re putting pressure on the ketchup and it responds as a
3 solid would. So from now on, just let the ketchup take its own sweet time coming out of the bottle - it will be faster! So, what makes Oobleck act like both a liquid and a solid? The mixture can be thought of as a colloidal suspension. The little grains of cornstarch do not dissolve in the water. They mix with the water, but they stay intact and solid. To further explain Oobleck’s strange behavior, imagine each granule of cornstarch surrounded by water. The surface tension of the water keeps it in the spaces between the granules. The cushion of the water provides quite a bit of lubrication and allows the granules to move around. Rapid movements cause the water to be squeezed out from between the granules, and the friction between them increases rather dramatically. Glurch is a polymer that the students can actually watch polymerize. By mixing glue, borax and water together, a sticky, gooey ball will form; this is Glurch. The glue is a polymer. The borax acts as a cross-linker; it reacts chemically with the glue to form new bonds between the glue molecules that link the chains of glue molecules together cross-wise. Because the newly formed Glurch has water trapped in its polymer matrix, it also exhibits a lot of the characteristics of solids and liquids. Though it seems solid, it will actually "pour" very slowly and it will take the shape of its container. Yet it sticks together and can all be picked up at once.
References: AIMS (1989). Oobleck. Lawrence Hall of Science. Berkeley, California.
Cobb, V. (1972). Science Experiments You Can Eat. J. P. Lippincott Pub. New York, New York.
Crowther, D. & R. Ross. Oobleck and the Mystery Powders. Available online at: http://unr.edu/homepage/crowther/opchem/oobleck.html
Kenda, M & P. Williams. (1992). Barron's Science Wizardry for Kids. Scholastic Inc. New York, New York.
Materials Research Society, Ontario Science Centre. Slimy Matter: The Toy Designer’s Challenge. Available online at: http://www.strangematterexhibit.com/teachersguide.pdf
Mosher, B. Oobleck and Glurch. Science Connection. University of Arizona. Available online at: http://student.biology.arizona.edu/sciconn/oobleck/oobleck.html
NASAexplores. Experiments with Oobleck. Express Lessons and Online Resources. Available online at: www.NASAexplores.com
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