# Physical properties of materials

This section introduces the meaning of each of the following physical properties and, where applicable, their units of measurement. It is likely that the teaching of this and the first topic (Mechanical properties of materials) will overlap. Most of these are probably more familiar from KS4 teaching than the technical terms applying to mechanical properties, although a more mathematical approach is needed.

- density
- melting point
- thermal conductivity
- electrical conductivity (resistivity)
- thermal expansion
- corrosion resistance

### Density Simulation

One of the many excellent simulations available from PhET at the University of Colorado, this activity allows students to change mass, volume and **density,** then observe the effect on an object in water. Relationships are explored and explained clearly by the observable changes. This would make an excellent follow-up activity to consolidate classwork or a homework assignment if you use the flipped classroom approach; students could then come with an understanding which you can help them clarify with further examples. This lesson on aerogels from TeachEngineering is aimed at much younger students but the applications of ultra-low-density materials in engineering is clearly relevant.

### Nuffield Science Calculations

As the title states, a guide to the many calculations in science courses. Although not recent the worked examples and exercises are still relevant and useful to help students gain familiarity with mathematical approaches. For this topic, of particular interest will be

**Density**: p43/44 of the book (p51/52 of the pdf)

**Resistance** from p32 of the book (p40 of the pdf)

Answers are at the end of the file.

### Making an Alloy

The experimental details support students in making (and then testing) solder, as used in industrial engineering applications. The extension activities suggested make this relevant for older students, and this provides a clear example of the effect of chemical composition on melting point, in a way that helps demonstrate what the concept means. Few metals can be shown to melt in the lab so alloys are the best route to showing actual materials in a realistic setting. Explanations of the trends seen in melting points are often abstract, but some data analysis can be carried out with industrial data, with straightforward descriptions such as this from General Chemistry Online.

### Thermal Properties

Topic 3 (heat transfer) places **conduction** in context. Other forms of heat 'loss' are explained, and the examples given for real world use help to show the importance, although some are a little dated (eg the space shuttle). A useful analogy linking thermal and **electrical conduction** may help some students to see common approaches, although the maths may be intimidating for some.

### Thermal Conductivity

This short video (and accompanying notes) show what conductivity is by showing what happens when ice is placed on materials which conduct at different rates. For a theoretical treatment, the definitions at SchoolPhysics are well worth a look (includes sample questions and a mathematical approach).

### Expansion and Contraction

This resource is intended to be adapted by teachers depending on the age of students. The simple effects seen are useful, it suggests, for students as young as ten (American grade 5) but the complex explanations make it relevant up to age seventeen (grade 12). Clearly students will be expected to consider these demonstrations of expansion in a subtle way. The context given is the problems faced by design engineers when specifying the materials for a space mission. Attention is drawn to the safety inplications of the activity described as a 'steam cannon'. Several of these practicals are equivalent to classic expansion circus activites like those described in pages 34-40 of this resource from the eLibrary.

### Episode 112: Resistivity

Lots of practical approaches here, helping students to understand the factors affecting **resistivity**. The editable Word document includes student instructions and equipment lists, as well as some follow-up questions to test progress. This would work well in combination with a simulation such as Conductivity from PhET, perhaps as a homework assignment.

### Metals Unit Guide

The practicals described here - mainly into **corrosion** and ways to prevent it - are intended for KS4 pupils but would provide a useful starting point for those less confident with their previous chemistry. Complete instructions are given with prompt questions for students to consider. Extending the practicals with more recent approaches to reducing corrosion, perhaps with novel materials, would be an easy way to engage students.

### Corrosion: the Virus of Engineering

This booklet has clear illustrations and would be useful to develop students' understanding of **corrosion**, once they are confident with chemical reactions and notation. The practical activities are mentioned but not described in detail. Rusting as an example of corrosion is dealt with on pages 14 and 15 of the textbook (p19/20 of the pdf).