A-Level Physics OCR B H557

3.2: Mechanical properties of materials

#3.2a(i)

simple mechanical behaviour: elastic and plastic deformation and fracture

#3.2a(ii)

direct evidence of the size of particles and their spacing

Examples: Scanning Tunnelling Microscope images; Rayleigh’s oil drop experiment

#3.2a(iii)

behaviour/structure of classes of materials, limited to metals, ceramics and polymers; dislocations leading to slip in metals with brittle materials not having mobile dislocations; polymer behaviour in terms of chain entanglement/unravelling

#3.2a(iv)

one method of measuring Young modulus and fracture stress.

#3.2b

Make appropriate use of:

(i) the terms: stress, strain, Young modulus, tension, compression, fracture stress and yield stress, stiff, elastic, plastic, ductile, hard, brittle, tough, strong, dislocation

by sketching and interpreting:

(ii) force–extension and stress–strain graphs up to fracture

(iii) tables and diagrams comparing materials by properties

(iv) images showing structures of materials.

#3.2c(i)

Hooke’s Law, $F = kx$ ; energy stored in an elastic material (elastic strain energy) = $\dfrac{1}{2}kx^2$ ; energy as area under Force–extension graph for elastic materials

*(loading only) *

#3.2c(ii)

$\text{stress} = \dfrac{\text{tension}}{\text{cross-sectional area}}$ ,

$\text{strain} = \dfrac{\text{extension}}{\text{original length}}$ ,

Young modulus $E = \dfrac{\text{stress}}{\text{strain}}$

#3.2d(i)

plotting force–extension characteristics for arrangements of springs, rubber bands, polythene strips, etc.

links to 3.2a(iii), b(ii), c(i), PAG2

#3.2d(ii)

determining Young modulus for a metal such as copper, steel or other wire.

links to 3.2a(iv), c(ii), PAG2

3.1.2

Sensing

4.1

Waves and quantum behaviour

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