Laminar flow occurs when there is no crossing of layers and no sudden changes in velocity. (Velocity at a point in the fluid is constant)
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Describe turbulent flow
Turbulent flow occurs when there is crossing of layers, sudden changes in velocity and eddies (whirls) form. (Velocity at a point in the fluid is not constant)
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Give the Stoke's Law formula, stating what each part means
F = 6πηrvterm F = viscous drag force; η (eta) = viscosity of the fluid; r = radius of object; vterm = terminal velocity
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What are the units of viscosity?
Nsm^-2
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What happens to the viscosity of a liquid when heated and consequently does the velocity of an object falling through it increase or decrease?
Viscosity decreases, velocity increases
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What happens to the viscosity of dry air when heated and consequently does the velocity of an object falling through it increase or decrease?
Viscosity increases, velocity decreases
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What is the upthrust of an object immersed in a fluid?
Upwards force equal to the weight of fluid displaced by the object
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Use upthrust to explain why metal ships don't sink
The hull is shaped to displace as much water as possible so as to counteract the weight of the ship and keep it afloat
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Describe the three forces acting on a body falling through a fluid
Weight acting down, upthrust and viscose drag acting upwards
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What is terminal velocity?
The speed at which an object falls once the drag and upthrust are equal and opposite to weight so there is no resultant force
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What is Hooke's law?
Force applied to a material is proportional to extension, F = k∆x
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What is the limit of proportionality on a force-extension graph?
The point beyond which force and extension are no longer proportional. (It is the end of the straight line force/extension graph that obeys Hooke’s law)
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What is the elastic limit of a material?
The point beyond which permanent deformation occurs and so the material does not return to its original length when the force is removed
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What is the yield point?
At the yield point a larger increase in extension occurs for a small increase in force
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What is stress?
Ratio of force to cross-sectional area σ = F÷A
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What is strain?
Ratio of extension to original length ε = ∆x/x
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What is the Young's Modulus?
Ratio of stress to strain
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What does s large Young's Modulus mean?
Stiff material
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How do you find the Young's Modulus on a Stress-Strain graph?
Gradient of the linear section
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What is strength?
The ability of a material to withstand stress
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What is elastic deformation?
Deformation that returns to its original shape when released
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What is plastic deformation?
Material doesn't return to original shape (permanently deforms) when force is applied beyond the elastic limit
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What is elastic strain energy?
Energy stored when a material is stretched or compressed elastically
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