# AS Unit 1 Topic 7 ```Edexcel AS Physics
Unit 1 : Chapter 7: Solid Materials
Prepared By: Shakil Raiman
7.1 Elastic Deformation
A
material undergoing elastic
dimensions when the deforming force
is removed.
 Example: Spring, Steel wire etc.
7.2 Plastic Deformation
A
material undergoing plastic deformation
remain deformed when the deforming
force is removed.
 Example:
modelling clay
7.3 Elastic and Plastic Deformation

Some material can behave in an elastic or plastic
manner depending on the nature of the deforming
force.

A thin steel sheet will deform elastically when
small forces are applied to it, but the huge forces
of a hydraulic press will mould the sheet into car
panels.
7.4 Properties of Solid Materials
Hardness: Hardness is a surface
phenomenon. The harder the material, the
more difficult it is to indent or scratch the
surface.
 Diamond is hardest which has a rating 10.
 Stiffness: A stiff material exhibits very small
deformations even when subjected to large
force.
 Steel etc.

7.4 Properties of Solid Materials
 Strength:
An object is strong if it can
withstand a large force before it
breaks.
 Steel
is strong but cotton is weak.
 Malleability:
A malleable material can
be hammered out into thin sheets.
 Gold
7.4 Properties of Solid Materials
 Ductility:
Ductile materials can be
drawn into wires.
copper
7.5 Stress
 Stress
(tensile/compressive stress) is defined as
force per unit cross-sectional area.

force
stress 
cross _ sec tional _ area

F

A

Unit: Pa (Pascal)
7.6 Strain
 Strain
is defined as extension per unit
original length.

extension
strain 
original _ length

l

l

Unit: no unit
7.7 Young’s Modulus
 Young
modulus is defined as the ratio of
tensile or compressive stress to strain.

stress
Young _ mod ulus 
strain


Fl
E 
 Al

Unit: Pa (Pascal)
7.8 Hooke’s Law



Hooke’s law states that, upto a given load,
the extension of a spring (or wire) is directly
proportional to the force applied to the
spring (or wire)
F  kx
where K represents the stiffness or spring
constant
7.9 Elastic Potential Energy or Elastic
Strain Energy
 The
elastic potential energy or elastic
strain energy is the ability of a
deformed material to do work as it
regains its original dimensions.

W  Fave x

1
W  Fmax x
2
7.10-1: Stress-Strain Graph
7.10-2: Stress-Strain Graph
 O-A
represents the Hooke’s Law region.
Strain is proportional to stress up to
this point. The Young modulus of
material can be found directly by
taking the gradient in this section.
 B is the elastic limit. If the stress is
removed below this value, the wire
returns to its original state.
7.10-3: Stress-Strain Graph
C
is the yield stress. For stresses
greater than this, the material will
become ductile and deform plastically.
 D is the maximum stress that a material
can endure. It is called ultimate tensile
strength (UTS).
 E or F is the breaking point. After E the
wire starts narrowing.
7.10-4: Stress-Strain Graph
7.10-5: Stress-Strain Graph
7.10-6: Stress-Strain of Rubber
The hysteresis
loop for stressstrain graph
represents the
energy per unit
volume
transferred to
internal energy