Materials Flashcards
Define fluid
Any substance that can flow. Can be a liquid or gas, solids can sometimes behave as fluids - sand.
Define density
mass per unit volume.
Define upthrust
An upwards force caused by an object displacing fluid.
If the object is completely submerged, the mass of the fluid displaced = volume of object + density of fluid. m=Vp.
State Archimedes Principle
The upthrust on an object is equal to the weight of fluid displaced.
What is a Hydrometer?
An instrument used to determine density of a fluid.
Define Laminar Flow
Fluid moves in parallel layers. The velocity is constant over time.
What is the effect of fluid flowing through a pipe?
Friction between the outermost layer and the pipe means this layer moves slower.
Define Turbulent Flow
Layers mix. The fluid becomes chaotic and swirling eddies form. Velocity in a particular place changes over time.
Define Viscosity.
How resistant a fluid is to flowing.
How is flow of fluid and viscosity related?
The rate of flow of a fluid is inversely proportional to the viscosity of the fluid.
Stokes Law
F = 6πηrv
Only applies to small spheres at low speeds. Drag force is directly proportional to radius and velocity.
pressure=
=Force/Area
=density x g x height
Terminal Velocity
the velocity of a falling object when its weight is balanced by the sum of drag and upthrust acting on it.
Define Hookes Law
Force needed to extend a spring is proportional to the extension of the spring.
A material obeys Hooke’s Law
if it has not passed the limit of proportionality
State Hooke’s Law
Force Applied = spring constant x extension.
ΔF = kΔ x
Define elastic strain energy.
Work done in deforming a material sample before it reaches elastic limit.
ΔEel = 1/2 FΔ x
Compressive force
Squashes the material causing a negative extension.
Tension
A force acting within a material in a direction that would extend.
Define Stress
Stress σ = F/A
Define Strain
Strain ε = Δ x/x
=extension / original length
Youngs Modulus, E
E = σ/ε =stress/strain =Fx/AΔ x
E is the stiffness constant of a material,
Limit of proportionality
Beyond this point stress is not proportional to strain.
Elastic Limit
The material is permanently deformed beyond this point. Sample will not return to original size when stress is released.
