KEY QUESTION
What are some of the properties of an unknown substance called "Oobleck"?

KEY CONCEPTS
Oobleck has properties of both solids and liquids, depending on its treatment.

POSSIBLE PRECONCEPTIONS
The behavior of Oobleck lies outside preconceived notions of the behavior of ‘normal’ matter.

GENERAL INFORMATION
FOCUS:                          Physical properties 
                                      Cooperative learning 
                                      Scientific research
GRADE LEVEL:                3-12 with extensions
GROUP SIZE:                 Small groups of 3-5 and whole class
SETTING:                      Classroom (with access to water)
TIME REQUIRED:          One class period
SCIENCE PROCESSES:   Questioning, designing experiments, classifying,
                                      formulating models, interpreting data, observing, using logic
METHOD :                     Teacher guided inquiry and discussion

MATERIALS LIST
Large mixing bowl Four boxes cornstarch
6 ¾ C. water 15 drops food coloring (usually green) 
Measuring cup 6 small bowls
Newspaper 
Drawing paper & markers

Making Oobleck: The above ingredients will make enough for six teams of students. Combine the cornstarch, water and food coloring in a mixing bowl about 45 minutes before the class starts. Just before class, stir the mixture again, adjusting the amounts of water and cornstarch until the Oobleck flows when you tip the bowl and feels solid when you hit it.

DOING THE ACTIVITY
The first step is to form student groups to investigate Oobleck. Make signs that describe the responsibilities for each group member and post them in the classroom. You also need to decide if you want to assign groups and roles or allow students to choose their own. Possible roles for individuals are:

the Facilitator   makes sure everyone in the group:
* understands what to do * is involved in the task * is being heard * gets help when needed

the Reporter
* makes sure everyone contributes * organizes the group report to the group report

the Materials Manager
* gets materials for the group * makes sure everyone has what they need to complete the task 

the Safety and Cleanup Manager
* ensures the job is done carefully * makes sure all group members and safely help clean up

the Checker
* collects work from all members * checks that all work is complete * turns in the work to the teacher

After the roles have been chosen or assigned, set the scene for your students by explaining that "Scientists have recently discovered a substance they call Oobleck. It is possible the Oobleck may occur naturally as oceans on some planets, and you’ve been called in as expert engineers to further investigate the properties of Oobleck."

Emphasize that Oobleck is safe to handle, but standard safety procedures still apply. Students are not to taste Oobleck, get it in their eyes or horseplay during the activity. They must also wash their hands after the activity. Assure the students that Oobleck will not stain clothing.

Tell the students that their job is investigate the properties of Oobleck. They will be expected to record their observations and share them with the class. If they are unclear on the concept of property (aspects of a substance that we can sense or that can be detected by instruments that extend our senses [i.e. microscopes and telescopes]) use a piece of chalk or other familiar object and have the students quickly identify some of its properties.

Give each group a container of Oobleck and allow them to begin their explorations. After several minutes, give them a large sheet of paper and markers so they can record their observations.

When the students are nearly done, tell them to finish their list of properties and have each group share its results.

CLEANUP
Oobleck will clog sinks so don’t pour it down the drain! Once it dries, it vacuums or sweeps up easily. You can save containers of Oobleck by covering them with plastic wrap and putting them in the refrigerator.

CLOSURE
If teams disagree on the properties of Oobleck, discuss these disagreements as a class and try to resolve them with further experimentation. There are several extensions for the Oobleck activity and you may simply want to tell your students they did so well, they’ve been selected for another mission. If this is your only Oobleck activity, tell the students what Oobleck is and discuss the possible explanations for its bizarre behavior (See Background).

EXTENSIONS

• Have your students think about what Oobleck might be made of. You can assign this as homework and have the results shared with the class the next day. 
• Send each student home with a small sample of Oobleck in a plastic bag or other air tight, unbreakable container. Remind them to keep it in the refrigerator when they aren’t using it. Ask your students to introduce Oobleck to their friends or family, and to notice how their family and friends react to this strange substance. Have your students share their experiences with the class. 
• For younger students, read the Dr. Seuss book Bartholomew and the Oobleck aloud to the class before the activity. 

When most fluids cool they become more viscous. This means that their resistance to flowing increases. Cooking oil is a common example. Such fluids are called Newtonian. But there is another class of liquids called non-Newtonian. Their viscosity increases not with temperature, but when the liquid is stirred or compressed. But naming the property doesn’t explain it, and some scientists have concentrated on the shape of starch molecules and how they fit together. Others have speculated that the electrical charge of the molecules is the key to Oobleck’s strange behavior.

If you decide to discuss this question with your students, begin by asking them for their ideas on why Oobleck behaves the way it does. Then ask them to imagine that they can see the individual molecules of cornstarch and water and to think about how they might act when being poured or pushed and pulled. This gives the students the opportunity to formulate their own models.

In one possible model, the starch molecules are compared to sand and water in a plastic squeeze bottle. The grains of sand are closely packed with a little water in between. The water’s surface tension doesn’t allow all the space between the sand grains to be filled with sand. Squeezing the bottle gently forces the sand grains to move against each other. This increases the spaces and allows more water to fill the spaces. The more gently you squeeze the more time there is for the water to fill the spaces and provide lubrication. But if you squeeze the bottle quickly, there isn’t enough water between the sand grains and friction between the sand grains resists the flow.

Although sand grains are much larger than molecules of starch, starch molecules are quite large and the mix of cornstarch and water may react very much like a mixture of sand and water. This is one explanation for why Oobleck flows like a fluid, but reacts as a solid when suddenly compressed.

Other scientists base their Oobleck models on chemistry. Cornstarch is made of long chain molecules called polymers. When water is added to cornstarch and the mixture is compressed, the molecules become "tangled" and are unable to slide easily against one another.

A third model suggests that starch molecules acquire an electric charge as they rub together. The faster they are rubbed, the more electrical attraction is created among the molecules. This causes the increase in viscosity.

You could end the discussion by explaining just how difficult it is to observe what’s going on at a molecular level just by observing the properties of a substance. Since there is no conclusive explanation of why Oobleck behaves as it does, suggest to your students that perhaps one day one of them will become a scientist and discover an explanation for the strange properties of Oobleck that everyone will agree is the correct one.