Cornstarch Suspension

Submitted by Tammy Knight from South Walker HS 

Materials: water, cornstarch, large bowl, mixing spoon, paper towels to dry hands 

In their play, children encounter objects with many different textures: hard and soft, smooth and rough, fuzzy, bumpy... They also experience the difference between solids and liquids and may even recognize that air is a gas you can breathe. This lesson demonstrates a special kind of substance, called a suspension, that is similar to liquids in some ways but similar to solids in others. It offers you many opportunities to talk about different textures with children. Measure one cup of cornstarch into a large bowl. Allow children to touch the cornstarch with their fingers. (Cornstarch is non-toxic, but don't let children eat it.) Ask them to describe it: the color, texture, and anything similar from their lives (flour, snow, etc.). In a large measuring cup, measure 1/2 cup water. Again, allow children to touch the water and talk about it. Slowly stir the water into the large bowl with cornstarch. (Aim for a mixture like thick pancake mix.) Ask children how they think it will feel. Will it be more like cornstarch or like water? Does it remind them of anything? Have children stick their hands into the mixture and move them slowly back and forth. Ask them how it feels. (The mixture feels like a liquid.) Next, ask the children to pick up some of the mixture and squeeze it. Now how does it feel? (When squeezed, it feels like a solid.)
Modifications and Extensions:
(1) Add a bit of food coloring to the water before mixing it into the cornstarch. Ask children to predict what color the result will be if you use 2 drops of red and 2 drops of blue (or another combination of colors).
(2) Try different ratios of cornstarch to water. What if you use one cup of water and one cup cornstarch? What if you use 1/4 cup water to one cup cornstarch? Ask children to predict what they think the mixture will feel like: what would happen if... Use words like "dry", "wet", "thick", and "thin", or make comparisons: will it feel like sand? like clay? Like milk?
(3) Try the same experiment with one cup of another non-toxic white powder in the kitchen – salt, flour, or sugar – instead of cornstarch. Again, ask them what they think will happen. Let children feel the result. Does it behave like the cornstarch mixture?