PHYA2 Materials Revision Notes

Just a few revision notes relevant to the AQA PHYA2 Materials Specification.

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  • Created on: 24-05-14 16:40
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AQA AS Physics A
PHYA2 ­ Mechanics, Materials and Waves
Revision Notes - Materials
Materials
Elasticity ­ An elastic material returns to its original size and shape when the forces which is
stretching or compressing it is removed.
Yield Point ­ Beyond the elastic limit, a point is reached which there is noticeably larger
permanent change in length. This results in plastic behaviour.
Breaking Stress ­ This is the maximum stress that can be applied to a material without it
breaking.
Stiffness ­ The measure of how difficult it is to change the size or shape of a material
o Thick Steel wire is stiffer than thin steel wire of the same length.
o Short steel wire is stiffer than longer steel wire of the same diameter.
o Steel is stiffer than copper of the same diameter and length, because copper
extends more per unit force.
Ductility ­ A ductile material can be easily and permanently stretched.
Hooke's law is that force is proportional to extension or stress is proportional to strain, however only
up to the limit of proportionality.
A spring constant, k, is applied to the extension to equal the force applied. This is written as F = kl
. You can calculate this constant by re-arranging the equation into the form k = F .
l
1 ­ Linear Region ­ Extension Force (obeys Hooke's law)
2 ­ Proportionality Limit ­ Beyond this point extension is no longer proportional to force (limit of
Hooke's law)
3 ­ Elastic Limit ­ Material begins to behave plastically. This is the point beyond which, when the
stress is removed, the material does not return to its original length.
4 ­ Yield Point ­ Material shows large increase in strain for small increase in stress.
5 ­ Breaking Stress (or Ultimate Tensile Stress) ­ The applied stress causes the material to fracture
(break).
Young's Modulus Equation
E = F l F l Fl
A ÷ l = A × l = Al

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AQA AS Physics A
PHYA2 ­ Mechanics, Materials and Waves
Revision Notes - Materials
Unit = Pa / Pascal or Nm-2 / Newton's per Metres Squared
Young's Modulus can be calculated from the force ­ extension graph:
l
E = gradient × A
Density
The density, , of a material is the mass, m, of a given volume, V.…read more

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