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# EVENTS, PROGRAMS, & COMPETITIONS

## Plastics and Rubber: What's the Difference?

Source: Original

#### Abstract

In this lesson students use observation skills to classify 10-15 common household items into two groups based upon their physical properties. The items are actually all examples of rubber or plastics.

#### Objectives

What should students know as a result of this lesson?

• Students will distinguish between observation and inference
• Students will identify similarities and differences between household products
• Students will sort and classify a group of 10-15 items
• Students will justify the reasons for their classification system

What should the students be able to do as a result of this lesson?

• Students should be able to use observation skills to classify a group of items based upon the properties of the items. Through the activity, students should be able to evaluate multiple viewpoints and distinguish between observation and inference.

#### Materials

• Ruler
• Balance or Scale
• 4-5 sets of 10-15 items made from rubber or plastic
• Examples:
• Rubber: rubber band, balloon, Totes shoe protectors, elastic waist band of pants, latex gloves, rubber tubing, exercise bands, bike tire
• Plastic: garbage bag, plastic shopping bag, plastic food wrap, drinking straw, plastic tubing, water bottle, toys, food storage container

#### Procedures

Engagement

Imagine going into the movie store to get the newest DVD you have been waiting to see. Instead of the DVD's being ordered neatly on the shelves, all of the store's DVDs are in a big pile in the middle of the store. What is the problem? (most likely will not be able to find the DVD of choice in a timely manner or even determine if it is available)

As a class, discuss the reasoning behind putting things into categories or groups. Brainstorm a list of things that are ordered or put into groups. (animal kingdoms, books in a library, clothes in a store, food in the grocery store)

What is the advantage of these categories? (one can determine what is available, takes less time to find something, inventory can be taken, allows for communication between people)

Tell the students that they will be placing 10-15 items into two groups based upon the physical properties of the items. The items need to be placed using observations, not inferences. Remind the students that observations are things that they can measure, see or feel. Inferences are judgments made based upon an observation. Hold up a textbook.

Ask students to quickly write down 3 observations and 1 inference for the book. (Observations: the book is blue, it has a hard cover, there is a picture of an apple on the front. Inference: the book will be easy to read, the book will be difficult to read, the book's pictures are helpful, the book is heavy.) Ask the students to tell the person sitting next to them the answers they wrote down before discussing several examples as a class.

Assessment: Monitor students' understanding of sorting and grouping by evaluating the answers they provide during the sorting brainstorm activity. Before proceeding, make sure that the students understand the difference between inferences and observations.

Exploration

Explain the procedures for the sorting activity to the students. During their observations, the students may touch and look at all of the samples. Students may use the balance or scale and ruler to gather observations. However, the students may not use the use sense of taste, for example. Next, remind the students that their senses are being used to make observations. They should not make guesses or inferences when sorting these objects.

Place 10-15 rubber and plastic items on each of 4-5 lab stations or tables around the room, but do not tell the students that they are examples of plastics and rubber, because students should be looking at physical properties and not trying to ID the items as fitting into someone else's labels. The students should be able to manipulate the samples to help identify their properties. Ask the students to create two separate categories on a sheet of paper and list each item under one of those categories.

Ask the students to meet in a group of 3-5 (grouping method and actual group number to be determined by the teacher). Students may move the items on their list from one category to another after talking with group members if they choose. The group needs to develop two categories and title the categories. Encourage discussion about the ways to sort and group the objects, but do not lead students towards the plastic and rubber classification.

Assessment: Monitor the students' work during the sorting to check that they are making careful observations and using safe practices. It is okay to answer students' questions regarding procedures, but do not lead students towards the plastic and rubber classification.

Explanation

Share the group work as a whole class. Each group should present their two categories with justifications. Encourage discussion about each group's system. As a class, look at the similarities and differences between each group's system.

Tell the students that they have been classifying the objects. To classify is to place objects into groups based upon similarities.

Tell the students that one way to classify these materials is "plastics" or "rubber". (Tell students that an elastic substance can stretch and bounce back. Rubber has elastic properties in varying degrees. Plastic, on the other hand, is not as elastic. It tends to deform when stretched, which is also known as necking.)

As a whole class, complete a chart for plastics and rubber. Place all of the plastic items in the plastic column and all of the rubber items in the rubber column.

Ask the class to brainstorm a list of additional items to add to each column. (big wheel tires, pens, markers, chewing gum)

Ask the students to answer the following challenge by writing several sentences. Invent an item that could be labeled plastic or rubber. What are its physical properties? How would someone use your item? (Example: I would make a bungee cord for a pencil. The bungee cord will be very thin and small, but very stretchy or elastic. It will be made of rubber. People will use my invention to help them keep track of their pencils. It will also keep people from dropping their pencils.)

Assessment: Monitor the students' answers to questions asked in the discussion about classification and the identification of plastics and rubber for accuracy.

Elaboration

Discuss the idea that plastics come in many different forms. "Plastic can be flexible or rigid; transparent or opaque. It can look like leather, wood, or silk. It can be made into toys or heart valves." (1.)

Discuss the properties of rubber. Rubber is also used in many of our everyday products from balloons to tubing and bandages to tires and shock absorbers. Today rubber can be natural or synthetic. However, the majority used is synthetic and produced by using crude oil. Crude oil is a nonrenewable resource. The process of recycling rubber can be difficult, but many benefits exist. (2.)

Which material would you use when constructing a container to protect an egg in an egg drop? Why? (Example: I would use rubber to protect an egg in an egg drop because it can be very elastic as shown by the waistband and rubber tubing in class. This property allows the material to distribute the energy during impact as in shock absorbers to protect the egg.)

Which material would you use when constructing a new toy? Why? (Example: I would use plastic to make a new toy because plastics are very versatile as shown by the plastic bag and water bottle in class. I could make the toy just about any size, and it could look like leather or be transparent.)

Which material would you use when building a new tool? Why? (Example: I would make a plastic screwdriver. Electricians could use the screwdriver because it does not conduct electricity. However, the screwdriver would still be strong.)

Optional Discussion: Explain your troubles if suddenly all plastics or rubber were removed from your daily life. Explain how life would be different and what kinds of challenges you might face or what kinds of improvements might be made to your life.

Assessment: Ask the listed questions to determine the students' understanding of the physical properties of plastics or rubber. Monitor the student responses for completeness and accurate ideas. (The questions have been left open to allow for student creativity and to encourage the students to justify their thinking.)

#### Prerequisites

Students should have previously discussed the idea of an observation being made using the senses. Observations include measurements.

Students should have previously discussed the idea of an inference being like a guess or a judgment made based upon an observation.

Students should know how to read a ruler and use a balance.

Students should be familiar with how to identify physical properties of an object. Physical properties are the way an object looks, its size, mass, shape, color, etc.

#### Best Teaching Practices

• Learning Cycle
• Hands-on/Minds-on Learning
• Inquiry
• Discussion
• Probing Questions

#### Alignment with Standards

NGSS Standards:

• MS-PS1-3 Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.

Common Core Standards:

• RST.6-8.1 Cite specific textual evidence to support analysis of science and technical texts.
• RST.6-8.3 Follow preciesly a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
• WHST.6-8.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.

National Standards:

• Science as Inquiry Grades 5-8
• Nature of Science Grades 5-8

Ohio Standards:

• Grades 6-8 Scientific Inquiry Benchmark A and B
• Grades 6-8 Science and Technology Benchmark A

#### Content Knowledge

Background information: What are plastics and rubber?

Plastics are used in a multitude of products. Water bottles, couches, clothing, and food packages are just a few examples. Plastic can be flexible or rigid or transparent or opaque. It can look like leather, wood, or silk. It can be made into toys or heart valves. There are more than 10,000 different kinds of plastics. The basic raw materials for plastic are petroleum and/or natural gas, (1.) which are both nonrenewable resources. Plastics are everywhere and can be recycled.

Rubber is also used in many of our everyday products from balloons to tubing and bandages to tires and shock absorbers. Today rubber can be natural or synthetic. However, the majority used is synthetic and produced by using crude oil. Crude oil is a nonrenewable resource. The process of recycling rubber can be difficult, but many benefits exist. (2.)

Classification: To classify is to place objects into groups based upon similarities. People use classification to order and simplify their daily lives. Books are classified in the library using the Dewey Decimal system. Stores classify movies based upon genre and then alphabetically. Scientists use classification to study everything from stars to living things. Classification also allows for efficient communication between people.

Physical Properties: Physical properties are the way an object looks, its size, mass, shape, color, etc. During the lesson, students should be making metric measurements regarding the objects mass and size.

#### Safety

• Safety goggles should be worn during the manipulation of the objects.
• Students with Latex allergies may need alternate materials.
• There are no disposal concerns.

#### Applications

Students categorize and classify objects on a daily basis. Furthermore, their lives are simplified by the classification and organization already present. Plastics and rubber are also items that students use on a daily basis possibly without realizing what the material is that they are using.

#### Assessment

You have just opened your "junk drawer" at home to find a wide array of objects. To help you find the objects in the future, classify the objects by placing them into three different categories. The first category will be rubber. The second will be plastic. You may label the third category with the title of your choosing. Please include at least 15 items in your classification system. The objects you choose are up to you, however, all of the items need to be items that would fit in the "junk drawer."

Example:

• Rubber: rubber band, key chain, bouncy ball, balloon
• Plastic: plastic bag, plastic spoon, ruler, whistle, plastic toy, mechanical pencil
• Metal: paper clip, staples, key, penny, nail

#### Other Considerations

Grouping Suggestions: Divide the students into groups of 3-5. Monitor the groups to insure that all students are participating with the group discussion. All students should have a part in the group presentation to the class.

Pacing/Suggested Time: This lesson should take approximately 2 class periods.

#### Printable PDF Worksheets

Students will generate their own charts and can use their own paper to complete the classification and answer the questions.