1. 4 TESTING MATERIALS Properties of materials
Classify and explore mechanical and electrical properties of materials
Explain the meaning of the term intensive property, with examples
Appreciate the need for log scales for representation of properties

2. Classifying materials
Look at the vast range of solid materials used in objects around you.
What general classes of material do they fall into?
Can you describe the internal structure of materials in these classes?

3. Investigating breaking stress
Measure the breaking force and breaking stress for a material
Use “plot and look” to identify outliers

4. Starter
How can we compare how strong/stiff different metals are when the wire samples we have are of different diameters for different metals?
Similarly, how can you compare how elastic/stretchy different metals are when the wire samples we have are of different lengths for different metals?

5. Force extension graphs and Young’s modulus
Record and interpret a load-extension graph for copper
Make an accurate and precise measurement of the Young’s Modulus of a material, estimating the uncertainties involved

6. Starter A wire of Material A fractures under a load of
100 N, while a wire of Material B fractures
under a load of 10 N.
Q1. What, if anything, can you conclude about the strengths of the materials A and B?
Q2. What further information would you need in order to make a valid comparison between materials A and B?

7. Stress, strain and Young’s Modulus
Define and then calculate these from experimental measurements

8. Olympus Mons imaged by Mars Reconnaissance Orbiter, September 2009

9. Measuring Young’s Modulus
Make an accurate and precise measurement of the Young’s Modulus of a material, estimating the uncertainties involved

10. Stress strain curves
Describe and explain the stress-strain curves for metals, ceramics and polymers

12. Note: Elastic limit and yield point are often very close to each
other

13. STRONG
HARD
TOUGH
STIFF

14. A
These are microscope images of the fracture cross sections of rods of two different materials. A A B
Which one has undergone ductile fracture, and which one brittle fracture? Explain your answer.

15. Electrical properties of materials
Investigate the relationship between material dimensions and resistance
Derive equations linking resistance, conductance, resistivity and conductivity

16. Measuring resistivity
Make an accurate and precise measurement of the resistivity of a material, estimating the uncertainties involved
Starter: Write down the equation for
working out the resistance R of a wire of
length L and area A. Compare with the
equation of a straight line. What should you
measure and plot in order to determine the
resistivity of the metal?

17. Making measurements
Review key considerations relating to experimental measurement

18. Uncertainty and Error How do they apply in this experiment?
Random uncertainties
Identify sources of measurement uncertainty and quantify them.
Which contributes the most to the uncertainty in the final answer?
Systematic errors
Identify limitations in the design of the experiment and explain how they could either be eliminated or reduced in effect.

19. Accuracy and precision
Accuracy: how close your measurement is to the accepted value
Precision: what range of values does your measurement span?
Accepted value = 110
108 +/- 4
125 +/- 2
111 +/- 9
85 +/- 40