Kid's Activity: Non-Newtonian Fluids -- Liquid or Solid?

by Melissa Jaramillo and Julie Snyder

Generally we classify things as liquid or solid or gaseous but there are some substances that don't behave like expected. Have you ever played with Silly Putty®, Ooze or Slime? (Or rather played along with the kids...surely parents don't "play.") You can slowly stretch silly putty out into a smooth, thin circle. Hit it with a hammer and it shatters! Is it a liquid because it flows? Or is it a solid because it is brittle? These materials belong to a special class of matter that doesn't obey the usual laws of viscosity.

Viscosity is a property of liquids that describes resistance to flow. Pour about a ½ cup of water into a glass. Try sloshing it around and pouring it out. See how easily it moves? Water has low viscosity because it flows quickly. Now pour about ½ molasses into a glass. Does it move as quickly and easily as water? It seems a lot more sluggish, doesn't it? Molasses has a higher viscosity because it flows much more slowly. Most fluids are Newtonian -- their ability to be poured depends on temperature. The warmer molasses is, the faster it will flow. Stick it in the microwave for about 30 seconds and pour it again. Is it faster or slower this time?

Non-Newtonian fluids like Silly Putty® and Slime depend on a different factor than temperature to determine their ability to be poured. A low stress such as pouring or pulling slowly allows non-Newtonian fluids to flow and stretch. A high stress such as hitting firmly or pulling sharply will cause the material to break.

Each non-Newtonian fluid is made of polymers. These polymers are molecules with long chains of repeating units. Take a box of paper clips and build several 18-inch long chains. Hold one end of your chains with one hand. Place two or more chains between fingers and slowly run your hand down the chains. You are demonstrating a low stress. The polymers (in this case, paper clip chains) can act like a liquid and slide past each other if stress is low. It is rather like running your fingers slowly through your hair. Your hand can move smoothly from the top to the bottom of the strands of hair.

If stress is high, like jerking a comb through tangles, the polymers tend to catch on each other and behave like solids. Try a hard, fast motion with the paper clips chains. Hold one end the chains in one hand. Wrap your other hand snuggly around all the chain. Move quickly toward the ends. Notice how some of the clips turn sideways and snag on other clips. Your "polymer" is now acting like a solid.

Below are four simple recipes for non-Newtonian fluids. Make one or all four as an introduction to these special fluids.

Corn starch putty
• ¼ cup corn starch
• 1-2 tablespoons water

If desired, add food coloring to water before mixing. Add water slowly, using fingers to mix until the mixture is gooey and fluid like. It has the right consistency if it will drip slowly from your hand and doesn't splatter when hit firmly.

Gluep
• 1 tablespoon glue
• 1 tablespoon water
• 2 teaspoons borax solution*
• popcicle stirring stick

*Mix 2 tablespoons borax in 2 cups water. Add a few drop lysol cleanser to retard mold growth.

Stir glue and water together. Add borax solution and continue to stir until a glob or gluep forms on the stick. Store gluep in a zip-lock bag. It will last several months.

Slime
• 2 tablespoons 4% polyvinyl alcohol solution (PVA)
• 1-2 drops food coloring (optional)
• 1/2 teaspoon borax solution (above)
• popcicle stirring stick

Pour PVA in cup. Add food coloring and stir. Continue stirring while adding the borax solution. Once the gel has formed, remove it from the cup and knead in your hands. Store in a zipper bag.

*Purchase 4% polyvinyl alcohol solution or make your own: Dissolve 1/3 cup of polyvinyl alcohol powder in a quart of water in a microwave-safe bowl. Heat in microwave on high for 8 - 10 minutes, stirring every minute. OR Stir 1/3 cup of polyvinyl alcohol powder in a quart of cold water in a pan. Heat over medium-high heat while stirring constantly. Cool before using. Add a few drops of lysol cleanser to retard mold growth.

Laundry starch/glue putty
• 2 tablespoon Elmer's school glue
• 1/2 drops food coloring (optional)
• 1 tablespoon Sta-flo laundry starch
• popcicle stirring stick

Thoroughly mix glue and coloring. Stir while adding starch. A thick lump will begin to form on the stick. Continue to stir thoroughly. Reach in and remove the putty with your fingers. Rinse well under running water. Store in a zipper bag.

Poke, pour, clap, strike! Squeeze it. Make it into a ball and throw onto a linoleum or tile floor. Pull it slowly; then quickly. Set a penny on the top to see if it sinks. Have a race across a plate! See how non-Newtonian fluids act!

Resources:
Homemade Slime and Rubber Bones!: Awesome Science Activities, by William R. Wellnitz
The Ultimate Book of Kid Concoctions: More Than 65 Wacky, Wild & Crazy Concoctions, by John E. Thomas, Danita Pagel and Danita Thomas
Super Science Concoctions: 50 Mysterious Mixtures for Fabulous Fun, by Jill Frankel Hauser, Michael Kline

Julie Snyder is a mom of six, interested in kids, pregnancy, birth, people and lives in the outlying Seattle area. Melissa Jaramillo is mom to many. She's passionate about building, encouraging, and strengthening families on this adventure known as parenthood!

Copyright © Melissa Jaramillo and Julie Snyder. Permission to republish granted to Pregnancy.org, LLC.