Stretching to Compare Properties: The Plastic Test
After a brief history of plastics, students look more closely as some examples from the abundant types of plastics found in our day-to-day lives. They are introduced to the mechanical properties of plastics, including their stress-strain relationships, which determine their suitability for different industrial and product applications. These physical properties enable plastics to be fabricated into a wide range of products. Students learn about the different roles that plastics play in our lives, Young's modulus, and the effects that plastics have on our environment. Then students act as industrial engineers, conducting tests to compare different plastics and performing a cost-benefit analysis to determine which are the most cost-effective for a given application, based on their costs and measured physical properties.
Students determine the physical characteristics, such as elasticity, of various plastics.Copyright 2010 Peter James Baker, Polytechnic Institute of NYU
The development of plastics has had a great influence on our daily lives, more than any other synthetic compound. Plastics have many physical properties that are far superior to traditional materials. For example plastic is able to keep liquids cold longer than glass, while being less breakable and lighter. Plastics are used in an overwhelming number of engineered designs from aircraft to automobiles to soda bottles with screw-on caps. To perform all these different roles, the unique physical properties of plastics are exploited. To design new plastic materials, engineers consider the stress and strain characteristics of various plastic formulations. Students gain an awareness of the prevalence of plastics in their everyday lives and learn about how the unique stress/strain relationships factor into materials choices made by engineers.
After this activity, students should be able to:
- Explain that different plastics have unique physical properties.
- Apply stress and strain to test the elasticity of various materials.
- Identify several limitations to the use of plastics on the material and ecological levels.
- Based on the physical properties and cost, determine which plastics are the most cost-effective for unique applications.