Density

Purpose

This is a simple investigation to determine the density of a variety of materials.

Activity

Depending on the level of the students, a discussion of density = mass/volume may be required.

Students consider whether there is a ratio between the density of the packaging material used and the density of the contents. Students will be conducting their experiments without the contents

Discuss how to measure mass and volume. Most students will suggest some sort of weighing device: kitchen scales, a spring or beam balance would be ideal. There may need to be some discussion, explanation and demonstration about volume. You should be able to guide them towards calculating the volume of a cube (depending on maths ability) or using displacement of water for irregular shapes.

Carry out the investigation and record and graph the densities of different materials on a mass against volume graph.

Discussion

Discuss the value of using low density packaging materials - students should suggest lightweight packaging is an advantage for transport, packing shelves, consumers, etc.

Extension

As an extension, discuss the density of waste packaging - most of the volume is air. Compare plastic PET drink bottles with aluminium beverage cans. Students could work out how many aluminium beverage cans fill a box, then how many PET plastic drink bottles fill the same box. Students try to crush the beverage cans and bottles and work out how many fit into the box now.

Note: Be careful when crushing cans: sharp edges = cuts! It's best to crush them by stomping on them on concrete or bitumen. Students can test the ideal way to crush an aluminium beverage can. The best way is to stamp on the side of the can then flatten the ends in, rather than try to flatten the can from top to bottom.

Discuss the implications of the results for transporting recyclable material. Emphasise that transport can be a significant cost factor in recycling.

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