Materials AS Physics

This is an overview f all the key points for AS physics materials.

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Physics Revision.
Materials.
Hooke's Law states that extension is proportional to force.
Hooke's law: Force is equal to stiffness constant (k) times the extension (e).
Hooke's law can be applied to springs and wires.
Hooke's law works just as well for compressive as tensile forces.
Hooke's law stops working when the load is great enough. Once the load is great enough the
material will reach the elastic limit and the line of the load, extension graph will begin to curve.
If you then increase the load past the elastic limit then the material will be permanently
stretched.
Plastic deformation: is when the material is permanently stretched. This is because the atoms
in the material move position relative to one another and do not return once the load is
removed.
A material stretched past its elastic limit shows plastic deformation.
Elastic deformation: is when the material returns to its original shape once the forces are
removed. This is because the atoms move slightly from their equilibrium position but once the
Stress and Strain.
Compressive forces squash the material and are though to be negative.
Tensile forces stretch the material and are thought to be positive.
Stress: Tensile stress is defined as the force applied (F) divided by the cross
sectional area (A). The units for stress are Newton meters to the power of minus 2 or
pascals.
A thin wire will stretch more than a tick wire and we say that it has a greater tensile
strenghth.
Ultimrte tensile strees is he measure of the strength of a material.
Strain: The tensile strain is defined by the change in length (E) divided by the original
length (L).
As you increase the tensile force the effect of the stress is to pull atoms apart. Eventually the
stress becomes so large the atom completely separate and the material breaks. On a stress,
strain graph this is the ultimate tensile stress point.
Elastic Strain energy is stored in a stretched material
1. Before the elastic limit, all the work done in stretching is stored as potential energy in
the material.
2. This stored energy is called elastic strain energy.
3. On a force extension graph the elastic strain energy is given by the area under the
graph.

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Equation for elastic strain energy is: E equals half times force times extension
Although because the material is obeying Hooke's law:
E equals half times stiffness constant times' extension squared.
The Young Modulus equation is: a measure of how of how difficult it is to change the
shape of the material.
Young's modulus is equal to Tensile stress divided by tensile strain.
The units for young's modulus are Newton meters to the power of minus 2 or pascals.…read more

Page 3

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The size of the force depends on viscosity: the higher the viscosity, the larger the
viscous drag force.
Viscosity:
The rate of flow depends on the viscosity: the higher the viscosity the slower the rate of flow.
Viscosity depends on temperature:
1. The higher the temperature the lower the viscosity.
2. The lower the temperature the higher the viscosity.
Viscous drag acts on objects moving through fluids.…read more