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Materials (Graphs ((Before P, gradient = k (Specific to tested object -…
Materials
Graphs
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Before P, the graph is a straight line through the origin - material obeys Hooke's Law
P = limit of proportionality - graph starts to bend at this point and the material no longer obeys Hooke's Law but would still return to its original shape if the stress was removed
E = elastic limit - at this point the material starts to behave plastically - after this point it will no longer return to its original shape if the load was removed
Y = yield point - material suddenly starts to extend without any extra load - the stress at which a large amount of plastic deformation takes place with a constant or reduced load
Hooke's Law
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There will be a change in length of a metal spring (extension/compression) when a pair of opposite forces are applied
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Elastic deformation occurs up to elastic limit:
- Material put under tension
- Atoms of material pulled apart from one another
- Atoms can move slightly relative to their equilibrium positions without changing position in the material
- When the load is removed, the atoms return to equilibrium distance apart and the material returns to its original shape
Plastic deformation occurs after the elastic limit:
- Material put under tension
- Atoms of material pulled apart from one another
- Some atoms in the material move relative to one another
- When the load is removed, these atoms do not return to their original positions and the material is permanently stretched
Stress, Strain and Young Modulus
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Density, Upthrust and Viscosity
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Stoke's Law
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Stokes' law used to calculate force due to viscous drag on small spherical object moving slowly with laminar flow
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Viscosity, η, is temperature dependent - liquids become less viscous with increasing temperature, gases more viscous
Laminar flow - all parts of fluid flow in the same direction and the layers do not mix - slow relative movement
Turbulent flow - all parts of the fluid get mixed up and the layers cross over - fast relative movement
