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What You Need:
- Measuring Cup
- Cookie Sheet or Tray – with sides!
- Gallon Size Ziploc Bag (optional – for storage)
Put 1 cup of cornstarch in a mixing bowl. Add water slowly to the cornstarch – about 1/2 cup. Mix the cornstarch and water with your hands until it starts to feel like a sticky glue. Try to pick up a handful of the goo. Squeeze your hand around the goo to make a fist around it. What happens? Now relax your hand. What happens now? Pour the goo onto a cookie sheet or tray. Make sure the sheet or tray has sides! Lay your hand on top of the goo and leave it there for a few seconds. Pull your hand straight up and watch what happens.
Cornstarch goo is an anomaly – that means it’s weird! It doesn’t act like it should. Sir Isaac Newton is famous for figuring out certain rules that apply to things on earth. One of his rules is that matter can take three forms: solid, liquid and gas. Liquids flow and take the shape of the container they are in. The cornstarch goo seems like a liquid because it flows off your fingers and it takes the shape of the container you put it in. But when you squeeze the goo…it turns into a solid. So which is it? A liquid or a solid? Cornstarch goo is called a non-Newtonian fluid because it doesn’t behave by Sir Isaac Newton’s rules.
Cornstarch goo is also a polymer. That means it’s molecules are arranged in a long chain. When the chain of molecules stretches…like the goo flowing off the fingers in this photo, the goo behaves like a liquid and flows. As soon as the goo has pressure applied to it – like when you squeeze it in your fist or when you rest your hand on it in the tray, it behaves like a solid and feels stiff and strong.
Usually matter turns into a liquid when it is heated and when liquid is heated it “gets runnier.” How easily a liquid flows is called viscosity. Water has a low viscosity and flows fast. Honey has a high viscosity and flows slowly. If you heat honey or lava…it flows faster. That is one of Sir Isaac’s rules too…that the viscosity of liquids goes up as the liquid is heated. With cornstarch goo, the viscosity changes when you put pressure on it instead of when you heat it. Weird again!
Science Project Idea: Get three bowls and measure 1 cup of a powdered substance into each bowl. 1 cup of cornstarch in bowl #1, 1 cup of baking soda in bowl #2 and 1 cup of flour in bowl #3. If you step back and look at the bowls they will all look pretty much the same – a bowl with white powder in it. Now pour 1/2 cup of water into each bowl and mix each bowl with your fingers. Do the mixtures behave the same? How do they behave differently? How would you describe each mixture? A solid or a liquid? You could also try baking soda and powdered sugar.
Here are some websites and books that will help you understand cornstarch goo:
- Exploratorium: Outrageous Ooze
- Science Bob: How to Make Slime
- The Museum of Science and Industry: Make Slime
- Steve Spangler Science: Non-Newtonian Cornstarch Recipe
- Instructibles: How to Make a Non-Newtonian Fluid
- WiseGeek: What is a Non-Newtonian Fluid?
- Science Rocks!: Slime Time (page 26)
- Naked Eggs and Flying Potatoes: Cornstarch Science – Quicksand Goo (pages 104-109)
Words to Know:
Polymers – Molecules arranged in a long chain.
Non-Newtonian Fluid – A fluid that doesn’t flow like you would expect when you put pressure on it.
Liquid – A state of matter. In the liquid state, matter can flow or take the shape of the container it is in.
Viscosity – How resistant to flowing a liquid is. Water has low viscosity and flows fast. Honey has high viscosity and flows slow.