An Oobleck Recipe and Fun Experiments With a Non-Newtonian Fluid

Oobleck is a strange and entertaining liquid that becomes a solid when pressed, hit or shaken and then returns to its liquid state when the stress is removed. Playing with oobleck is great fun for both children and adults. It’s quick, easy and safe to make, although experimenting with oobleck can get messy. I teach in a high school, and my students in the youngest grade right through to the oldest grade love making oobleck and exploring its behavior.

Oobleck is named after the sticky green substance in the Doctor Seuss book “Bartholomew and the Oobleck”. In this book a magical spell causes oobleck to fall from the sky on to the kingdom of Didd, annoying everyone.

Ingredients

1 cup of water
1 1/2 to 2 cups of cornstarch (which is called cornflour in the U.K.)

(Any ratio of about 1 part water to 1.5 to 2 parts cornstarch will work.)

Instructions

• Add the water to a bowl.
• Rub some cornstarch between your fingers before you add it to the water - it has an interesting feel.
• Gradually add the cornstarch to the water and mix with a spoon (or your hand).
• Once you’ve added 1/12 cups of cornstarch add more cornstarch slowly and start mixing with your hand so that you can see when the oobleck is ready.
• Squeeze the oobleck as you add the cornstarch. If it forms a ball as you squeeze and then liquifies when you stop squeezing it's ready to use.
• If you make a mistake, add extra water or cornstarch until the oobleck forms.
• Some people like to add food coloring to the oobleck for fun, but don't add too much color because it can stain skin and clothing. Add a small amount of the food coloring to the water before you mix the water with the cornstarch.

You might want to wear an apron during these potentially messy experiments, and to cover the surface which is being used for the experiments!

• Squeeze some oobleck to make a solid, then open your hand and watch the solid turn back into a liquid.

• Roll some oobleck into a ball. Open the hand that is holding the ball and watch the solid oobleck change into a liquid.

• Create an oobleck ball and try to pass the ball to someone else before it liquifies.
• Try bouncing an oobleck ball on the rest of the oobleck.
• Measure how long it takes the strands of oobleck to drip into the container from a specific height once a ball has liquified in your hand.
• Rest your fingers on the surface of the oobleck and let them sink, then try to pull your fingers out of the oobleck quickly.

• Try using a hand or fist to slap or hit some oobleck. A large aluminum tray is good for this experiment.
• If you have the resources, fill a large container (or two smaller containers) with oobleck. Try walking on the oobleck. You will have to move your feet rapidly to avoid sinking.

• Place a speaker on its side. A speaker with strong base sounds is best. Place a metal tray or a disposable plastic plate containing oobleck on top of the working speaker, or place a small amount of oobleck on strong plastic wrap on top of the speaker. (Don’t use a valuable speaker for this process in case the oobleck container breaks.) This is one of the most interesting oobleck experiments. The oobleck forms strange, changing tendrils as it solidifies in response to the vibrations coming from the speaker. Two of my senior students demonstrated this during a project on non-Newtonian fluids. They used an iPod touch to drive the speaker.

Don’t pour oobleck or cornstarch down the drain! The drain may block if oobleck solidifies inside it. Instead, pour or scrape oobleck into the garbage. Dried oobleck becomes a powder and is easy to brush into a garbage can. Wash your containers and hands (and any other body parts or clothing covered with oobleck) only when most of the oobleck has been removed and put in the garbage container. Warm water will help get the oobleck remnants off hands.

Most fluids are classified as “Newtonian” fluids. They’re named after Isaac Newton, the famous scientist who lived from 1643 to 1726 and made many extremely valuable contributions to our present knowledge of science. Newton stated that fluids have a constant viscosity (ability to flow) if the temperature is kept constant. Applying a force or stress to the fluid doesn’t change its viscosity. An example of a Newtonian fluid is water. If you press your hand on water in a container, the water doesn’t resist the force that you’re creating or change its viscosity, and your hand falls into the water; if you try to walk on water you’ll sink.

Non-Newtonian fluids behave differently from Newtonian fluids when a force or stress is applied to them. If you press, hit or shake a non-Newtonian fluid, its viscosity changes. In some fluids the viscosity increases, while in others it decreases. In oobleck the viscosity increases with stress as the oobleck resists the applied force, and the liquid becomes a solid.

Oobleck is a colloid, containing cornstarch particles spread through the water. The starch particles exist as long chains. When the oobleck is not under pressure, the cornstarch chains and water molecules slide past each other, and the oobleck is a liquid. When pressure is applied, water molecules are temporarily pushed out of the way and the cornstarch molecules are pushed together. The starch molecules can no longer slide over one another and the oobleck appears to be a solid. When the pressure is removed, water moves in between the starch molecules again and the oobleck returns to its liquid form.

Traditional custard is a mixture of egg yolks with milk which is heated until it thickens. While I was growing up, however, “custard” meant Bird’s Custard to me. This is sold as a powder containing cornstarch mixed with artificial flavor and color. If custard powder is mixed with water in the right proportion, custard oobleck forms. If you had enough of the custard oobleck you could put it in a large container as shown in the third video in this hub, and then you could walk on custard!