Chapter 4 – Testing Materials (12 lessons including test)
Lesson
4.1 Making
the
best
choice
Content
Range and variety of materials
Activities
Homework
Activity 20E ‘Compressive
testing’
Activity
30E
‘Hardness
testing’
Activity 40E ‘Tear testing’
Activity 50E ‘Measuring
density’ (needs 0-5 kg
balance!)
Activity 60E ‘Comparing
thermal conductivities’
Activity
70E
‘Electrical
conduction’ (use multi meter
as ohm meter)
Activity
80E
‘Optical
properties’
Qs 10S ‘Exploring the range of
materials’
At
least
one
from
home
experiments Activity 90H, 100H,
110H, 120H, 130H
Reading 10T ‘Steel – the most
important material?’
Reading 20T ‘Materials from
nature’

Classify materials as metals, glasses, ceramics or
polymers.
 Explore mechanical properties of materials such as
density, tensile strength, hardness, electrical
properties such as conductivity, optical properties.
 Know precise meaning of terms strong, hard, ductile,
dense, conductor, insulator.
 Know the meaning of the term intensive property, and
identify which mechanical properties considered are
intensive ones.
 Classify a given material as metal, glass, ceramic or
polymer from appearance, mechanical, electrical
and/or optical properties.
Lesson 1: Students examine circus of materials belonging to
the material classes: metals, glasses ceramics and polymers.
Now do the circus of experiments: 50E: density; 30E:
hardness; 70E: conductivity; 20E: compressive testing. It may
be best to leave the tensile strength practical to the second
session, and use it to generate a load-extension graph: see
lesson 4 and 5 for data needed to measure Young’s modulus.
A possible challenge activity: determine mystery material
(lead) by measuring density and resistance.
PIA Jan. 07 Q4
03/03/2016 2:39 AM
A. M. James, Matthew Arnold School, Oxford
1
Lesson
Content
• Record and interpret a load-extension graph for
copper
Lesson 2: Do Activity 10E/150E to generate a load-extension
graph for copper. Use at least 250 cm of 30 SWG copper wire,
with a metre stick butted up against the pulley block as a
reference scale, and a pointer attached from the wire made
from a piece of sticky label.. At this stage, a simple load (in g)
against extension (in mm) graph can be plotted, but provided
that the wire diameter and length have been noted, the data
can be used in a later lesson to calculate the Young’s modulus
and yield stress of copper.
Activities
Homework
Activity
150E
‘Good
measurement of Young’s
modulus’ Note: 250 cm of
0.31 mm diameter copper
wire (30 SWG) is suitable.
For nylon use 0.10 mm
diameter wire.
Qs 10S ‘Exploring the range of
materials’
At
least
one
from
home
experiments Activity 90H, 100H,
110H, 120H, 130H
Reading 10T ‘Steel – the most
important material?’
Reading 20T ‘Materials from
nature’
PIA June 07 Q1
Qs p79
Qs 20C ‘The Bronze age’
Qs 30C ‘Portraits in plastic’
Reading 60S ‘More about log
scales’
4.2
Better
buildings
Tensile testing, stress, strain and Young modulus

Investigate breaking stress of a range of materials to
develop familiarity with ‘plot and look’ idea for repeat
measurements.
 Appreciate the need for intensive measurements of
stress and strain when testing and comparing
materials.
Lesson 3: Breaking stress of materials using Activity 100E.
This is a good activity for ‘plot and look’, provided that the
cotton thread option is adopted. When using cotton thread,
create a loop knot by doubling over the end of the thread and
tying a knot. There is a reel of cotton thread of suitable
thickness in the A level Chapter 4 tray. The paper strip
experiment is much more fiddly and requires Hoffmann clips.
Use the spreadsheet in Activity 100E to show how to anlayse
the data in terms of mean, range, spread, standard deviation,
03/03/2016 2:39 AM
A. M. James, Matthew Arnold School, Oxford
Activity 100E ‘Plot and look:
measuring breaking stress
of materials’
Activity
150E
‘Good
measurement of Young’s
modulus’
Reading 40S ‘Hooke’s law and the
Young modulus’
2
Lesson
Content
and the calculation of stress values, noting that stress is an
intensive property. Go through the uncertainty treatment as
per Activity 100E.
As a demonstration, load nylon fishing line or metal wires to
destruction to generate a load extension graph: discuss how
the graph varies with the dimensions of the specimen and so
lead into a definition of stress and strain (see Activity 150E).
 Know definitions of tensile and compressive stress
and strain, Young’s modulus.
 Use the relevant equations for stress, strain and the
Young’s modulus to perform calculations.
 Know that the stiffer a material, the greater its Young’s
modulus.
Lesson 4: Go through the formal definitions of tensile stress
(strength) and strain. Note also the compressive equivalents
of tensile properties, noting which sorts of materials are strong
in compression and which in tension. Do some sample
calculations of stress and strain, and introduce the Young
modulus as the gradient of the stress strain graph. The
question sheet stress, strain and the Young’s modulus covers
all the key points. Note the scaling up problem in Hollywood: a
giant insect would not be able to support its weight as its
weight scales as r3, while the area of its legs scales as r2.
Discuss maximum height of mountains being governed by
maximum compressive stress at base.

Make an accurate and precise measurement of the
Young’s Modulus of a material, estimating the
uncertainties involved
Lesson 5-6: Measure Young’s modulus, and yield stress if
possible, using Activity 150E (4 sets) and/or Young’s modulus
apparatus. The data obtained in lesson 2 can be used. Typical
results are provided on the Excel worksheets embedded in
03/03/2016 2:39 AM
A. M. James, Matthew Arnold School, Oxford
Activities
Homework
Qs 50D ‘Stress, strain and
the Young’s Modulus’
Qs 45S ‘Calculations on
stress
strain
and
the
Young’s modulus’
Qs 50S ‘Measuring the
Young’s modulus’
Qs 10E ‘Making estimates
about mechanical behaviour
of materials’
PIA Jan 06 Q10 on
maximum
height
of
mountains
Qs 50D ‘Stress, strain and the
Young’s Modulus’
Qs 45S ‘Calculations on stress
strain and the Young’s modulus’
Qs 50S ‘Measuring the Young’s
modulus’
Qs 10E ‘Making estimates about
mechanical
behaviour
of
materials’
Qs p87
Activity
150E
‘Good
measurement of Young’s
modulus’ Note: 250 cm of
0.31 mm diameter copper
wire (30 SWG) is suitable.
For nylon use 0.10 mm
diameter wire.
Qs 50D ‘Stress, strain and the
Young’s Modulus’
Qs 45S ‘Calculations on stress
strain and the Young’s modulus’
Qs 50S ‘Measuring the Young’s
modulus’
Qs 10E ‘Making estimates about
3
Lesson
Content
Activity 150E for copper, nylon and rubber.
For YM apparatus, see sheet on Using YM apparatus.
Equipment required: YM apparatus, 30 SWG copper wire, 100
g masses on hanger, metric micrometer, tape measure
In the second session, plot graphs and analyse data, making
an estimate of the overall uncertainty in the measurements
(see Activity 150E for more detail).
 Know the meaning of the terms elastic deformation,
plastic deformation, yield stress, fracture stress,
ductile fracture, brittle fracture, stiff, strong, tough,
hard.
 Sketch stress-strain graphs for ductile and brittle
materials, identifying the key regions/points on the
graphs as described in the previous bullet point.
 Sketch stress-strain graphs to illustrate the terms
strong and stiff.
 Interpret stress-strain graph to determine Young’s
modulus, yield stress and strain, fracture stress and
strain of different materials.
 Interpret 2-D plots of (for example) strength versus
density to select appropriate materials for a particular
application.
 Know which types of material are likely to show ductile
or brittle fracture behaviour.
Lesson 7: Elastic and plastic deformation, brittle and ductile
fracture. Issue a stress-strain graph for mild steel, or use the
graph generated from the previous lesson. If not done so
already, work out the Young’s Modulus from the initial
gradient. Students use the sheet Properties of solid materials
from stress strain curves and annotate their plots in the
relevant places, recording yield stress and ultimate stress
values as well. Examine electron micrographs of the two types
of fracture (on OHTs). Do the questions on Interpreting stress
strain curves.
Begin filling in material template for a typical metal, leaving
structural explanation until Chapter 5.
03/03/2016 2:39 AM
A. M. James, Matthew Arnold School, Oxford
Activities
PIA G491 Jan. 09 Q8; Jan.
07 Q8; May 08 Q6
Homework
mechanical
behaviour
of
materials’
Qs 40S ‘Analysis of tensile testing
experiments’
Qs 40S ‘Hooke’s Law and the
Young’s Modulus’
Reading 150T ‘Fantastic fibres’
Qs p87
Begin filling in material template.
4
Lesson
4.3
Conducting
well,
conducting
badly
Content
Resistance and conductance, resistivity and conductivity
Activities
Homework

Recall and use the equation R=V/I to determine the
resistance of a material.
 Investigate how the resistance of a material changes
with length and cross sectional area.
 Know that the resistance of a material is proportional
to its length, inversely proportional to its area, the
constant of proportionality depending on the material
and its temperature.
Lesson 8: Recap electrical resistance as measure of how
difficult it is to get current through a material, and recap
equation R = V/I. Recap electrical resistance measurements
from lesson 1 and how comparisons can be only be made with
resistance if lengths and cross sectional areas are the same,
indicating the need for an intensive property relating to
resistance. Class experiment: variation of R with l and A (use
nichrome wires, twisting together to increase area). Use multi
meters as ohm meters.
Go through the derivation of R = l/A from the experimental
observations, and the corresponding equation G = A/l, noting
the intensive properties of resistivity and conductivity. See
also Physics-online “Resistance in a wire”. Sample
calculations on sheet Resistance, conductance, resistivity,
conductivity.



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As well as class practical,
can demonstrate some of
the following:
Activity 310E ‘Measuring
resistance of good
conductors’
Activity 330E ‘Measuring
resistance of two insulators’
Activity 340E ‘How the
dimensions of a conductor
affect resistance’
Activity 345E ‘Introduction to
resistivity using conducting
paper’
Physics-online “Resistance
in a wire”
Understand the origin of the equation R = l/A.
Recall and use the equation R = l/A to do
calculations on the electrical properties of materials.
Know that resistivity () is an intensive property that is
used for the comparison of the electrical properties of
materials.
A. M. James, Matthew Arnold School, Oxford
5
Lesson
Content
 Know the meaning of the term conductance (G), and
that G=1/R = I/V.
 Use the equation G = A/l to do calculations on the
electrical properties of materials.
 Know that conductivity ( =1/) is an intensive
property that is used for the comparison of the
electrical properties of materials.
Lesson 9: Formal treatment of R = l/A and G = A/l, if not
covered in the previous lesson. Sample calculations, including
unit conversion, cross sectional area calculation, blocks as
well as wires. See sheet Resistance, conductance, resistivity,
conductivity,
Activities
Homework
Selected questions from
resources listed to right as
exemplars in notes
Qs 70S ‘Electrical properties’
Qs 80S ‘Resistivity and
conductivity calculations’
Qs 100S ‘Conductance and
conductivity’
Qs 20E ‘Making estimates about
the electrical properties of
materials’
Qs p90
PIA May 08 q8; Jan. 08 Q8

Determine the resistivity of, and hence identify, a
range of unknown metals and/or metal alloys.
Lesson 10: Determination of resistivity using Activity 350E,
OR
more simply use multimeter to measure R directly (each
student needs: multimeter, 2 leads, 2 crocs, metre stick,
access to 30 SWG nichrome, 30 SWG constantan, sellotape,
wire cutters) This experiment is essential preparation for the Quality
of Measurement coursework task. Analysis: graphical method of
plotting R versus 1/A, slope = l. Estimate uncertainties in each of
Activity
350E
‘Good
measurements of electrical
resistivity’
Qs from lesson 8 homework tasks
Qs 90X provides a good set of
review questions for the work of
the whole chapter.
the measurements. Conclusion: precision of micrometer has largest
overall impact on uncertainty in final result.
Note: for 30 SWG nichrome, 1 m has resistance of about 13.4
ohms; for 30 SWG constantan, 1 m has resistance 6.6 ohms.
4.4
Problems of

03/03/2016 2:39 AM
Review measurement experiments to derive a set of
key factors that should always be considered when
A. M. James, Matthew Arnold School, Oxford
6
Lesson
measuring
mechanical
and
electrical
properties
Content
Activities
making measurements.
Lesson 11: Review the three key measurement experiments:
100E (breaking stress), 150E (Young modulus), 350E
(resistivity) to draw out the key points in making
measurements:
1. dealing with properties that vary from sample to sample
(e.g. tensile strength)
2. measuring small quantities (e.g. extension and wire
diameter)
3. effect on uncertainty if a quantity is raised to a power (e.g.
cross-section proportional to diameter squared)
4. the possible presence of systematic error (e.g. yielding of
support under tension; contact resistance).
Key points to bear in mind when making measurements:
1. Watch out for natural variations between samples; plot the
values and find the range.
2. Start with a rough measurement or calculation, to identify
the problems to be solved.
3. Small quantities, close to the resolution of an instrument,
are hard to measure with low uncertainty.
4. If A = d 2, the percentage uncertainty in A is double that in d
5. To improve a measurement, identify the largest source of
uncertainty and try to reduce that first.
6. Look out for systematic errors and try to remove them.
Chapter 4 test.
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A. M. James, Matthew Arnold School, Oxford
Homework
Qs p94
Qs
210D
‘Calculating
uncertainties: Chapters 4-5’
with
Qs p96
7