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Non-Newtonian Fluids

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Author: Marc Rosner

Matter generally takes on one of three different phases (forms): solid, liquid, or gas. But did you ever play with Silly Putty?

  • In a solid, atoms and molecules are in close, fixed positions, vibrating in place in a crystal structure. In a liquid, these particles are close together, too, but they move around at various speeds. Solids and liquids have definite volumes. In a gas, atoms and molecules are much farther apart, whizzing around space with no fixed volume.

What phase is it? Silly Putty is one of many substances that does not neatly fall into one phase category. Like slime and goop, Silly Putty shows elements of being both a solid and a liquid. These weird chemicals and mixtures are sometimes called non-Newtonian fluids, implying that they somehow do not obey the traditional laws of physics described by Isaac Newton (1642–1727). Newton, however, was a very wise man and probably would have enjoyed playing with Silly Putty and explaining its novel properties.

Materials

  • Silly Putty
  • safety goggles
  • water
  • metric measuring cup and spoons
  • cornstarch
  • pie tin
  • food coloring
  • small weights (such as steel washers or fishing weights)
  • 2 small bowls
  • Elmer's glue
  • borax (available in supermarkets in the laundry detergent section)
  • mixing spoon
  • medium-size bowl
  • 4 packages of unflavored gelatin
  • glycerin (available at drugstores)
  • muffin molds or shallow cups
  • vegetable oil spray
  • timer
Liquids take the shape of whatever container they are in.

Procedure

Examine Silly Putty for both its solid and its liquid properties. First study it in its container. Notice it has flowed like water to fill the bottom of the container. The surface is flat. Press it gently. It yields because the molecules are not in fixed positions. Now pull the putty apart quickly, with as much force as you can. It snaps apart like a solid. Roll it together into a ball and throw it against the wall or floor. Again it behaves like an elastic solid, bouncing back. The warmer Silly Putty is, the more it behaves like a liquid; the colder it is, the more it behaves like a solid. Now put on your safety goggles and make your own putty, goop, and slime.

Non-Newtonian Fluids

To Make Cornstarch Putty

  1. Mix warm water with cornstarch in a pie tin. Start with a small quantity of cornstarch–I5 ml per 125 ml of water. Increase the amount of cornstarch 15 ml at a time to obtain different properties, each time mixing it in well and examining the result before adding more. You can make this and the other non-Newtonian fluids more colorful by adding a drop or two of food coloring.
  2. Investigate how the putty's properties vary depending upon how you stress it. Pour it, hit it, cut it, and study its response to these actions.
  3. You can do a quantitative study with small weights to see what the putty can support.

To Make Goop

  1. In a small bowl, mix 350 mL of warm water, 475 mL of Elmer's glue, and a drop or two of food coloring. This is solution 1.
  2. The glue contains polyvinyl acetate molecules. The borax connects these molecules into long chains called polymers. Polymers are significant because of their great length and strength–polymers often twist around themselves like a tangled bundle of yarn.
  3. In a second small bowl, mix 20 mL of borax (sodium borate), and 230 mL of warm water. This is solution 2.
  4. Stir both solutions gently until they are uniform, then pour solution 1 into solution 2 without mixing or stirring. Your goop is done.
  5. Test your goop. How does it differ from putty? Can a blob of goop support a small weight? If you pull the goop apart slowly, does it stretch like gum, or break like a solid? What if you pull it apart quickly? What happens when you twist it, first slowly and then quickly?
  6. Wash your hands after handling the goop, as it can irritate your skin.

To Make Homemade Slime

  1. In a medium-size bowl, mix four packages of unflavored gelatin with 200 mL of warm water. Add 25 mL of glycerin, and a drop or two of food coloring. Stir gently.
  2. Spray some muffin molds or shallow cups with vegetable oil.
  3. Add the slime to the molds and let it set for 20 minutes.
  4. Remove the slime and handle it gently. How does slime differ from putty and goop?

Non-Newtonian Fluids

References

  • Janice VanCleave's 200 Goey, Slippery, Slimy, Weird, and Fun Experiments by Janice VanCleave (New York: John Wiley & Sons, 1993).
  • Kitchen Chemistry: Science Experiments to Do at Home by Robert Gardner, ed. Jane Steltenpohl (parsippany, N.J.: Silver Burdett/Messner, 1989).
  • Science Experiments You Can Eat, rev. ed., by Vicki Cobb (New York: HarperCollins Children's Books, 1994).
  • Vicki Cobb's Kids' Science Page:
  • www.vickicobb.com
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