Mystery Material: Is it a solid or a liquid?

Students will learn about the mystery substance by observing and manipulating it. Students will be able to experience a solid that acts like a liquid or a liquid that can behave like a solid. Students should be able to identify how the material is different from a typical solid and liquid. Students can think about other substances or materials that behave like the mystery substance. By doing this inquiry activity, they will be able to understand theories about what causes plate tectonics. Students will be able to relate the properties of the substance to the fluid layer of the earth's mantle called the asthenosphere. Geologists have hypothesized that this layer can help explain the theory of plate tectonics. In advanced classes, students may be able to infer about the molecular forces in the material. They may also be able infer how other materials like this might be used by humans. Students could also explain how materials with this unusual property could be used as armor.

This activity is mainly intended for middle school aged classrooms. This can be used as an engagement or exploring activity at the beginning of an earth science lesson when discussing the different layers of the earth. It could also be used as an activity during a chemistry unit when discussing the different phases of matter. Since it is very inquiry based, it would work well with students with or without prior knowledge of the subject. It can be easily related to a number of different topics and age levels. For more advanced students or high school aged classrooms, intermolecular forces could be discussed as well as how materials with this property could be used by humans (example - body armor). Discussions on colloids or non-Newtonian fluids could also be done.

Materials

Cornstarch
Newspapers
Measuring cups
Large bowl, pan, or container
Water
Spoons
Food coloring (optional)

Students will

1. Cover table top with newspaper to avoid too much of a mess.
2. Mix cornstarch and water into a bowl (food color optional).
   Use 2 parts cornstarch for every 1 part water. Slowly add water and mix with fingers until all of the power becomes wet.
3. Add more water until the material feels like a liquid.
   If the material is too powdery then add more water, if the material is too watery add more cornstarch.
4. Students will observe and manipulate material. (if it dries out slowly add water, if it gets too watery slowly add more cornstarch)

Things students can do and questions they can answer in observation journal or notebook:

1. Pick up a handful and squeeze it. What does it feel like?
2. After squeezing it let go. What happens to the ooze?
3. Tap the surface of the ooze with your finger. Tap it with a spoon. What does it feel and look like? How is this different than if you tapped water?
4. Pick up a handful and roll between your hands. Stop rolling and observe. What happens?
5. Push your fingers slowly through until you touch the bottom of the bowl. What do you observe?
6. Try to quickly punch your fingers through until you touch the bottom of the bowl. What do you observe?
7. How is this mystery substance different from a typical liquid?

Discussion questions or assignment questions

1. Describe ways the ooze acted like a solid.
2. Describe ways the ooze acted like a liquid.
3. Is it more like a solid or a liquid? Why?
   
   If done as part of an earth science lesson:
   
4. How can you relate this to layers of the earth and plate tectonics?
5. How can knowing that solids are not always hard or rigid explain plate tectonics?

For advanced students: Explain your observations in terms of how the molecules are behaving.

This activity will be messy. Make sure work areas are covered, and I would remind students to wear clothing that can get dirty. Students will enjoy working with the material, which will turn watery or flaky over time. Make sure students slowly mix water and cornstarch. Adding too much water at one time will make it too watery. Students may need help answering some of the questions related to plate tectonics. I have tried this as an exploratory activity without having written questions and answers, only as a class discussion. Having students answer questions and drawing pictures of the layers of earth with this activity may help reinforce the material.

Class discussion can be an easy assessment. Groups can discuss their observations and then share them with the class. Collecting observation journals and answers to the questions can also be easily done. This is more of an exploration activity and concepts observed and learned can be translated into other class discussions and assignments.

6.I.B.1 - Scientific inquiry
6.II.B.2 - Mixtures and pure substances
7.I.B.4 - Scientific investigation
8.III.A.1 - Movement of crustal plates
9-12.II.A.7 - States of matter, interaction of particles
9-12.II.A.6 - Compounds
9-12.II.A.9 - Elements and compounds