SummaryStudents learn about viscoelastic material behavior, such as strain rate dependence and creep, by using silly putty, an easy-to-make polymer material. They learn how to make silly putty, observe its behavior with different strain rates, and then measure the creep time of different formulations of silly putty. By seeing the viscoelastic behavior of silly putty, students start to gain an understanding of how biological materials function. Students gain experience in data collection, graph interpretation, and comparison of material properties to elucidate material behavior. It is recommended that students perform Part 1 of the activity first (making and playing with silly putty), then receive the content and concept information in the associated lesson, and then complete Part 2 of the activity (experimenting and making measurements with silly putty).
Bioengineers study biological materials and how they function in healthy and diseased states. Since biological materials exhibit viscoelastic behavior, engineers must understand this behavior in order to fully characterize these materials. Engineers may also design devices that come into contact with biological materials. So, to ensure effective and successful device performance, engineers must understand how the biological environment reacts to the forces that a device imposes. Polymers such as silly putty also exhibit viscoelastic behavior and can be used to demonstrate and learn about the functioning of biological materials.
An understanding of algebra and how to solve algebraic equations, as well as experience graphing using Microsoft Excel. Cover the Viscoelasticity lesson content before completing Part 2 of the activity.
After this activity, students should be able to:
- Demonstrate two viscoelastic material behaviors (strain rate dependence and creep) with silly putty.
- Explain the effects of borax concentration on the material properties of silly putty.
- Graph collected data using Microsoft Excel.
- Explain sources of error in experimental data.
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Students make two different formulations of imitation Silly Putty with varying degrees of cross-linking. They witness how changes in the degree of cross-linking influence the putty properties.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science,
technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN),
a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics;
within type by subtype, then by grade, etc.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
- Use the mean and standard deviation of a data set to fit it to a normal distribution and to estimate population percentages. Recognize that there are data sets for which such a procedure is not appropriate. Use calculators, spreadsheets, and tables to estimate areas under the normal curve. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment? Thanks for your feedback!
- Represent data with plots on the real number line (dot plots, histograms, and box plots). (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment? Thanks for your feedback!
Each group needs:
- 2 plastic containers, for mixing water and glue, and water and borax powder (such as GladWare tall square or deep dish plastic containers, ~ 6 x 11 x 5-in and 6 x 9 x 7-in [L x W x H]; no lids needed)
- 3 disposable spoons
- 3 plastic bags that seal (such as Ziploc sandwich bags)
- 2 ounce (1/4 cup) measuring cup for fluids ($1 at Dollar stores)
- 12-inch or longer ruler
- stopwatch ($3)
- white school glue, 6 ounces
- marker, to label plastic bags
- soap and water, for cleaning containers and hands
- access to computer with Microsoft Excel or similar spreadsheet and graphing application
- Creepy Silly Putty Data Analysis Worksheet, one per student
To share with the entire class:
For the design project in this course, we need to understand how the biological materials in our bodies behave in response to forces, so that we can design devices that will not harm the body. Today's activity introduces you to the intriguing behavior of viscoelastic materials—including biological materials.
For today's activity, you will make silly putty! Silly putty is made by mixing together three ingredients: glue, water and borax. What do you think the borax does to the glue to form silly putty? Think about it a minute and write down your hypothesis.
Your group will make three batches of silly putty, each with a different concentration of borax (high, medium and low concentrations). Take a moment to think about it and then write down your predictions of how you think the different borax concentrations will alter the silly putty: How will the material properties change? Which concentration do you think will be easiest to make?
creep: The response of a viscoelastic material when a constant force is applied. The displacement of the material increases over time until equilibrium is reached.
polymer: A material that is composed of a compound that is repeated to form a chain. Common examples are plastics and rubbers.
strain: Deformation of a material divided by its initial length.
viscoelastic: Materials that exhibit both viscous and elastic characteristics when undergoing deformation.
This hands-on activity has two parts. It is recommended that the activity and its associated Viscoelasticity lesson be conducted in the following order:
- Conduct Part 1 of the activity: Student teams make three batches of silly putty with different concentrations of borax and qualitatively explore silly putty behavior.
- Conduct the Viscoelasticity lesson: Students are introduced to the concept of viscoelasticity and some of the material behaviors of viscoelastic materials, including strain rate dependence, stress relaxation, creep, hysteresis and preconditioning.
- Conduct Part 2 of the activity: Students measure the creep time demonstrated by the silly putty they made in Part 1 to explore the role of borax in the formation of silly putty and quantitatively understand how its concentration alters material properties.
For more information, refer to the Background section in the Viscoelasticity lesson.
Before the Activity
- Gather materials and make copies of the Creepy Silly Putty Data Analysis Worksheet.
- (optional) During Part 1, use the four slides of the Making Silly Putty Instructions PowerPoint file to guide students on how to make the silly putty. During Part 2, use the four slides of the Creepy Silly Putty Experiment Instructions PowerPoint file to provide guidance on how to measure the creep time of silly putty.
- With the class, conduct the Introduction/Motivation section of this activity.
- Divide the class into groups of three students each.
With the Students: Part 1 — Making and Playing with Silly Putty
- Have each group collect two containers, three spoons and three plastic bags.
- Make: In one container, mix 1 ounce warm water with ¼ teaspoon borax.
- In the other container, mix together 2 ounces glue and 2 ounces warm water until you have a uniform consistency and color. (It is important that this solution be uniform, with no areas of excess water, or it prolongs the mixing time in step 5.)
- While stirring, slowly pour the borax mixture into the glue mixture. Be sure that all of the borax is transferred into the glue solution.
- When the solution starts to thicken, mix with your hands instead of the spoon. Continue to mix until a uniform solution is achieved and NO water is present.
- Store in a plastic bag labeled: low concentration.
- Thoroughly clean both containers and discard the spoon.
- Repeat steps 2–7 two more times, with 1 teaspoon borax (medium concentration) and 2 teaspoons borax (high concentration), respectively.
- Make sure all bags are labeled with the concentration level and your team name.
- Play: Encourage students to explore the unique properties of silly putty (viscoelastic behavior) and note the comparative differences in responses to force by each batch. For example: Stretch the silly putty at different rates, roll the silly putty into balls and let it sit on a table, and form each batch into a cylinder shape and hold one end of it, etc. Tip: While exploring the silly putty properties, be careful not to mix up the different batches or lose track of the borax concentration of each batch since teams will need to know this for Part 2 of the activity.
- Have students share and discuss their observations as they pertain to materials behavior. Does silly putty behave like an elastic solid or a viscous fluid? (Expected observations: If you slowly stretch the silly putty, it is very pliable and seems to stretch forever; it behaves like a viscous fluid. If you quickly stretch the silly putty, then it breaks immediately, seems stiff, and behaves like a solid with little elasticity. The same material has two very different responses to a force depending on how fast the force was applied. Over time, the balls of silly putty on the tabletop deform and spread out, like a viscous fluid. However, you can hold the silly putty without a container and use your hands to deform it into different shapes, like a solid. While holding a cylinder of silly putty by one end, the silly putty slowly stretches and elongates from its own weight. So, silly putty behaves like an elastic solid and a viscous fluid depending on the forces that are applied to it. Exhibiting both characteristics is the definition of a viscoelastic material; this will be revealed to the students and explained in more detail during the Viscoelasticity lesson.)
- Ask students to describe and discuss how the observed silly putty responses are different from that of springs (refer to the Mechanics of Elastic Materials lesson and Using Hooke's Law to Understand Materials activity). (Points to make about the differences in responses between silly putty and springs include: Springs do not continue to deform over time when you hold one of their ends or change shape when left on a tabletop, but silly putty does. When a force is applied to a spring, it always deforms the same amount, independent of how fast the force was applied. Silly putty exhibits different responses to a force depending on how fast the force is applied. Springs instantaneously return to their original shapes after a force is removed, and without outside assistance, whereas silly putty requires time and/or outside assistance, such as a container or the force from your hands, to return to its original shape.)
- Have students revisit their earlier predictions and look ahead to the lesson material. Use the questions provided in the Assessment section.
- Next, present and/or review with students the content in the Viscoelasticity lesson.
With the Students: Part 2 —Silly Putty Experimentation and Testing
- Have each group collect the bags of silly putty that students made in Part 1 (all 3 borax concentrations), a ruler and a stopwatch.
Assign students the following specific group roles to perform during the experiment and data gathering:
- 1 person forms and holds the silly putty at the same height
- 1 person holds the ruler and checks initial placement of the silly putty
- 1 person operates the stopwatch
- 1 person records data (if groups of three, assign this fourth role to everyone)
- Form the silly putty into a cylinder with a diameter of approximately 1.5 inches. (It is very important that the diameter and shape of the silly putty be consistent for each trial. See the Troubleshooting Tips section for details.)
- Hold the ruler vertically so that the "0 inches" mark touches the table.
- Hold the top end of the silly putty cylinder so that the bottom of the silly putty cylinder is positioned 6 inches above the table.
- Immediately start the stopwatch. Keep the hand holding the silly putty stationary and at the same height until the silly putty touches the table.
- Record the amount of time it takes for the silly putty to touch the table.
- Repeat steps 2–6 with the same silly putty batch two more times, recording the times.
- Complete steps 2–7 for each silly putty concentration. (Expect students to notice that as the concentration of borax increases, the amount of time for the silly putty to creep 6 inches also increases. If students obtain questionable results, run more trials and throw out bad data.)
- Have students reflect on the data they collected by asking them the questions in the Assessment section. Discuss as a class or assign students to write down their own answers.
- Conclude by handing out the worksheets for students to complete and hand in.
Part 2 works best when specific team jobs are assigned to students at the beginning of the activity and not varied throughout the activity.
Part 2 of this activity is very sensitive to human variability and error. The force driving the creep behavior is the weight of the silly putty. If the silly putty is not formed into a uniform cross section cylinder and held in the same way for every trial, the results will have a lot of variability and error. If students obtain questionable results, run more trials and throw out bad data.
Questions & Predictions: Today you will make silly putty by mixing together glue, water and borax.
- What do you think the borax does to the glue to form silly putty? Record your hypothesis.
- Your group will make three batches, each with different concentrations of borax (high, medium and low concentrations). Write your predictions of how you think the different borax concentrations will affect the silly putty: How will the material properties change? Which concentration do you think will be easiest to make?
Activity Embedded Assessment
Revisit Predictions: After completing Part 1, have students revisit their earlier predictions and look ahead to the material that will be covered in the associated lesson. Discuss as a class or assign students to write down their own answers. Ask the students:
- Was your hypothesis correct about how the borax concentrations changed the material properties of the silly putty? Explain. (As the concentration of borax increases, the amount of time for the silly putty to creep 6 inches also increases.)
- Did you see any differences while making the three concentrations?
- Is silly putty an elastic solid or a viscous fluid. Which one? Why? (This will be answered and further discussed during the Viscoelasticity lesson. The answer: Silly putty is both!)
Data Reflection: After completing Part 2, have students reflect on the data they collected and answer the following questions.
- Did you have any variations in the time it took for the silly putty to creep 6 inches when you repeated the experiment for the same concentration? (Expect students to say yes.)
- If so, what factors could have caused this? (Possible answers: Human variability and error, for example, if the silly putty is not formed into a uniform cross section cylinder, held in the same way for every trial, and held at the same height while it is deforming.)
- Why do you think the concentration of borax altered the viscoelastic properties of silly putty? (At this time, just have students predict why they think borax is altering the properties of the silly putty. The answer will be revealed to the students and discussed in more detail during the lesson. Answer: Glue is a polymer, so on a molecular level it consists of strings of compounds, similar to a plate of spaghetti. Borax reacts with the glue and binds the strings together [cross-linking], similar to when a plate of spaghetti starts to dry and all the noodles stick to each other. The more borax you add to the glue, the more cross-links that form, resulting in a stiffer material.)
Data Analysis: Assign students to complete the Creepy Silly Putty Data Analysis Worksheet, in which they create bar plots in Excel, calculate the standard deviation of creep time for their data, and answer questions to probe their results for meaning and conclusions. Review their answers to gauge their mastery of the material.
- For lower grades, have students only complete Part 1. Then follow with a class discussion on how viscoelastic materials (polymers and biological materials) behave differently when they are stretched at different rates (refer to the viscoelasticity lesson for a detailed description of this behavior). Demonstrate the difference in behavior when the silly putty is stretched slowly vs. rapidly.
Additional Multimedia Support
Refer to the Everyday Polymers lesson and its Let's Make Silly Putty activity in which students make two different formulations of silly putty to explore the chemical identities of polymeric materials and learn how chemical composition and cross-linking affect their physical properties.
ContributorsBrandi N. Briggs; Marissa H. Forbes; Denise W. Carlson
Copyright© 2011 by Regents of the University of Colorado.
Supporting ProgramIntegrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.
Last modified: October 20, 2017