Sorting plastic

Sorting plastic

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about identifying and describing physical properties of plastic objects.
a) i)
In your group read the information in the box below. Check that everyone understands what a physical property is.
A property of a material is a natural part of the material and can be used to identify it. Physical properties can be observed (you can describe by looking at them) and/or measured in some way.  All materials have more that one property. There are lots of different sorts of plastics. One way we can group plastic objects is by the physical properties of the plastic they are made from. Some physical properties are hardness, smoothness, transparency (how much light it lets through), flexibility (how much it bends), strength, and stretch-ability.
 
ii)
Fill in the table below by writing the name of something in your classroom that has the property described. The first row is done for you.
   
Hard Desk top Soft Cushion
Smooth   Rough  
Lets light through   Blocks light  
Bendy   Stiff  
Strong   Easily broken  
Stretchy   Not stretchy  

STOP: Ask your teacher or another group to check your answers.
b) Your teacher will give you 6 things made of plastic. In your group decide where each of these objects will fit for each property. The first one is done for you. It shows the property of smoothness of some objects, from smoothest to roughest. (Your objects might be different from the example.)
  i)
smoothest  roughest
 
 
 
ii)
  
 

hardestsoftest

 
 
 
iii)
 
 

lets light throughblocks light
 
 
 
iv)
 
 

bendystiff

 
 
 
v)
 

most stretchyleast stretchy
 
c)
Here are 4 tests students used to test a property. Try each test before you answer the questions.
 
   
Test 1: One end of each plastic object was held at 0 on the ruler, and then the other end pulled as far along the ruler as it could go.
 
  i)
Circle the property that was being investigated.
 
smoothness       bendiness       let light through       stretchiness       hardness
 
  ii)
How could you measure this property?
 
 
 
   
Test 2: A student tried to make one end of each plastic object touch its other end.
 
  i)
Circle the property that was being investigated.
 
smoothness       bendiness       let light through       stretchiness       hardness
 
  ii)
How could you measure this property?

 
 
 
   
Test 3: A nail was scraped across each plastic object.
 
  i)
Circle the property that was being investigated.
 
smoothness       bendiness       let light through       stretchiness       hardness
 
  ii) How could you measure this property?

 
 
 
   
Test 4: Each plastic object was held up to the light.
 
  i)
Circle the property that was being investigated.
 
smoothness       bendiness       let light through       stretchiness       hardness
 
  ii)
How could you measure this property?
 
 
 
 
d) The teacher recorded the students' rules for sorting their plastic in one of the two columns below.

 
Column A Column B
  • by the shape;
  • by where it is found in the home;
  • by whether it was used for cooking or drinking
  • whether it was hard or not;
  • whether they are very flexible or not;
  • whether they can be scratched or not;
  • whether light can pass through or not
 
 
i)
 
In your group, decide which properties you think scientists would use to group plastic objects (circle one).
 
 
Those in Column A                or                     Those in Column B
 
  ii)
Give your group's reason for your answer.  
 
 
 
 
 
 
 
 
Task administration: 
This task can be completed with pencil and paper and other equipment.
 
Equipment:
for each group, 6 common plastic objects, (e.g., supermarket bag, plastic container, ruler, cup, comb, pen, spoon, glad wrap, empty milk container, etc.), ruler, nail
  • The task is done in small groups (3-4 students). Encourage students to negotiate their group responses.
  • It does not matter if there are different plastic objects for each group.
  • It is important that students understand the science language used about investigating properties to ensure this task is valid. The teacher could read the first box to students, and discuss, before they answer the questions that follow.
  • You can check students' understanding of the science vocabulary used, before you begin, by using the table, Science words you need to know.

Science words you need to know:

Words Meaning Example
classify sort into groups that have something in common We can classify fabric by whether it is waterproof or not.
property a natural part of a material that can be used to identify and describe the material Some properties are colour, hardness, and bendiness.
material the stuff that anything is made of. Scientists call it matter. Some examples of materials are plastic, wood, metal, wool and water.
observable properties things you can see

Some examples are colour, stretchiness, and smoothness.
Some examples are absorbency, stretchiness, and hardness.
measureable properties things you can measure Some examples of ways to measure are a ruler, a thermometer, or a scale that describes with words, e.g. very rough, rough, a little bit rough, smooth, very smooth.
Level:
3
Curriculum info: 
Science, Investigating in science, Material World, Understanding about science, Material World
Key Competencies: 
Using language, symbols, and texts
Keywords: 
properties, physical properties, vocabulary, plastics, group assessment, key competencies
Description of task: 
Task: Describe and compare some physical properties of plastic objects and identify the properties scientists might use for classifying materials. Assessment focus: classifying using physical properties.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.
 
Capability: Gather and interpret data
This resource provides opportunities to discuss when we look very carefully and notice lots of things it helps us describe how things are similar and different.
 
Capability: Use evidence
This resource provides opportunities to discuss properties/evidence used to group materials. 
Science capabilities: 
Gather and interpret data, Use evidence
Answers/responses: 
a)

i)
ii)

No response required
Answers will vary. Check that students understand the vocabulary that describes the property.
b)

i)
ii)
iii)
iv)
v)

 Answer given
Answers will vary.  For answers ii)-v), check that students:

  • Apply the property described to the plastic objects;
  • Understand the comparative forms of the adjective, e.g. 'est', most, least;
  • Can order the degree of the property exhibited by the plastic objects;
  • Can use the continuum to indicate the relative amount/degree of the property exhibited
c)


i)
ii)

i)
ii)

i)
ii)

i)
ii)

Test 1
Stretchiness
Accept any answer that enables students to compare the lengths. Example: Compare the length of the plastic object before and after it was stretched by reading the numbers on the ruler.

Test 2
Bendiness
Accept any answer that enables students to quantify how much the plastic object has bent. Example: using a protractor, or equating with the numbers on a clock face.

Test 3
Hardness
Accept any answer that enables students to describe the scratches made. Example: A scale from no mark to a deep mark that compares how easy it is to scratch the plastic.

Test 4
Light let through
Accept any answer that enables students to compare the amount of light that passes through the plastic. Example: The number of layers (thickness) before it cannot be seen through
d) i)
ii)

Column B
The science ideas of observable and/or measurable properties are what scientists use because they are stable in unchanging conditions (whereas how plastics are used depend on people and how people/cultures see the ‘uses’).
Based on trial samples of a total of 32 Y6 students in November 2007 and February 2008.
Teaching and learning: 

Background
The concept of property is an important science concept but it is also difficult to develop. In this task, the focus is on physical properties and the words used to describe these properties. At this level the scientific terms that apply to materials may be unfamiliar to many students; hence some everyday property terms are used in the task. A table that compares some of the scientific and everyday terms of physical properties can be found in the Teacher information of Paper money for Monopoly (version A).

Question d) introduces the idea of measurable physical properties. Asking students how they could measure a property is scaffolding students’ thinking to extend from simple observable properties of materials towards considering how they can compare or rank materials' properties.

Developing and applying the precise language to describe properties strengthens both the Key Competency, Using language, symbols, and text, and the nature of science strand, Communicating in science, by assisting students to recognise that science vocabulary often carries specific meanings that are not always the same as its everyday meanings. Go to Language barriers.

Scientists create and use scales to compare properties, e.g., scales measuring temperature, length, hardness, etc, to enable them to share their ideas and to know that they are talking about the same thing. This idea is inherent in both Understanding about science and Communicating in Science.

Diagnostic and formative information: 

The trials revealed that students often:

  • could not think of physical properties themselves; and
  • some students tended to focus on the object, e.g., the ruler, bag, etc, rather than the material it was made from.
For question d) half the initial trial students' responses focussed on human uses as a property. By providing them with a choice (Column A or B), they were able to select the correct answer, but most could not give a sensible reason why. Discussion of this point involves students exploring their understanding about science and how the scientific community functions.
The word "property" caused problems for the trial students. They were familiar with it in everyday terms of "possessions/belongings" or "home" but it was foreign to most in its scientific meaning. This is a good example of a word with a specific scientific meaning that is different to its everyday meaning. For more information, go to Language barriers.
Next steps: 
Developing scientific vocabulary
If students struggle with describing physical properties, they need lots of experiences in a variety of contexts to develop their vocabulary. Other suitable contexts are soil, rocks, metals, paper, or any other material.
A fun activity is to ask students to think of the silliest use they can for a material. They then describe why it would be ridiculous, and the teacher can help students to understand that these reasons relate to its properties. For example, concrete would not make a good parachute, because it is heavy. [Reference: Rosemary Feasey, Scicon Conference (Auckland), 2002.]

Focussing on the material rather than the object
If students describe the property of the object rather than the material it is made from, for example, describing the bag rather than the plastic, spend time differentiating between the structure of an object and the material used.

Using scales
Activity 1 (page 8) in Building Science Concepts Book 36, Heat on the move, explores the nature of science ideas that:

  • scales are constructed by scientists;
  • scales can be used across contexts; and
  • unlike vocabulary, scales are not dependant on context, e.g., "hot" when describing a cup of tea is quite a different temperature from when describing weather

Similar activities could encourage students to either investigate scales constructed by scientists, e.g. for measuring length, or to construct their own simple scales. Other groups of students could try out the scales to see if they get consistent measures.

Discuss how scientists construct these scales to help them describe properties accurately, and they are not a "real thing". To emphasise this they could look at 2 different scales, e.g., Celsius and Fahrenheit, and why it is important to know which scale is being used. Students could also compare and critique the scales they construct. They could also look at which scales are less accurate (those such as a scale from 1-5, because it is more subjective).

A continuum is used to compare properties in this resource.  A continuum is another way of communicating in science (and other curriculum areas).Provide practice in both reading and constructing continua in a range of contexts. Asking students to stand on a line to express how much they agree or disagree with a statement is a useful beginning activity, and can be useful as a quick check or for a discussion starter, where they talk about why they chose to stand on that point.

The following Building Science Concepts books focus on properties of materials:
  • Book 5, Fur, feathers, and bark.
  • Book 13, Aluminium.
  • Book 32, Introducing metals.
  • Book 33, Working with metals.
  • Book 48, Fabrics.
  • Book 60, Rubbish.
  • Book 61, Recycling.
 
Other ARB resources relating to classifying using properties: