Materials Flashcards
What type of energy is stored in an object that has been stretched?
Elastic potential energy
What is the yield point?
The point at which the object will experience a large extension without an increase in stress
What does the area underneath a force-extension graph represent?
The area us equal to the elastic potential energy stored in the spring
What unit is the Young’s Modulus measured in?
Nm⁻² or Pa
State the equation for Young’s Modulus.
Stress / Strain
What is the unit of strain?
There is no unit, it is a ratio of the extension and original length
State the equation of strain?
Extension / Original length
What is elastic deformation?
Deformation where a material can return to its original shape and size, after an applied stress is released. Any work done is stored as elastic potential energy
Why will a uniform object with a density greater than that of the fluid it is submerged in, always sink?
- Upthrust = weight of displaced fluid
So therefore maximum upthrust is ρ(f)Vg - Weight = ρ(o)Vg
Therfore if ρ(o) is greater than ρ(f) then the weight will always be greater than the upthrust and the object will sink
What determines whether an objecy floats or sinks?
The balance of the weight and the upthrust of the object. If the weight exceeds the upthrust, the object will sink
What is the density of a material?
Its mass per unit volume
What is the unit of stress?
Nm⁻² or Pa
State the equation of Hooke’s Law.
F = kx
State the Stoke’s Law equation
F=6πrηv
F = viscous drag force
η = viscosity of the fluid
r = radius of sphere
v = velocity of sphere
What is required for Stoke’s Law to apply?
Laminar flow
What shaped objects does Stoke’s law apply to?
Small, spherical objects
What is the unit for density?
kgm⁻³
State the equation for stress?
Force / Cross-sectional area
What is stress?
The force per unit area experienced by an object
Explain Hooke’s Law.
The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
What is the Young’s Modulus?
A measure of how much force is required for a given extension, regardless of the object’s dimensions
What does Stoke’s Law allow you to calculate? What conditions are necessary?
The viscous drag force that a small, spherical object experiences when falling at low speeds through a viscous fluid with laminar flow
What does the gradient on a force-extension graph represent?
The elastic constant (k)
What is breaking stress?
The maximum stress that an object can withstand before fracturing
What is the elastic limit?
The point beyond which the object will no longer deform elastically and will instead deform plastically. Beyond this point the object will be permanently deformed
What is plastic deformation?
An object has undergone plastic deformation if it no longer returns to the original shape after the deforming forces are removed. It will have permanent deformation. Some work done will be dissipated as heat
What is the limit of proportionality?
The point beyond which Hooke’s Law is no longer obeyed - the force and extension will no longer be directly proportional to each other
State the two equations used to calculate elastic potential energy.
E = 1/2 fx
E = 1/2 kx^2
What is Archimede’s principle?
When an object is submerged in a fluid the weight of the fluid is displaced. This produces the force of upthrust
What happens to the viscosity of liquids and gases when temperatures increases?
For gases, viscosity increases as temp increases
For liquids, viscosity decreases as temp increases
What is laminar flow?
Its where a fluid moved with uniform lines in which the velocity is constant over time. In laminar flow, the lines are streamlines
What is the ultimate tensile stress?
The ultimate tensile stress is the maximum stress that the material can withstand before the breaking stress
What is viscous drag?
The frictional force between a solid and a fluid.
What is the coefficient for viscosity?
A numerical value given to a fluid to indicate how much it resists flow
What is terminal velocity?
The velocity of a falling object when its weight is balanced by the sum of the drag and upthrust acting on it
What is viscosity?
A meaure of how resistant a fluid is to flowing
What is turbulent flow?
Where fluid velocity in a particular place changes over time, often in an unpredictable manner. It is chaotic and ‘eddies’ form which are swirls, it increases drag
What is a hydrometer?
A hydrometer determines the density of a fluid. It has a constant weight so will sink lower in fluids of less density. there are scale markings on the side of the hydrometer to indicate the density of the liquid
What are streamlines?
Lines of laminar flow in which the velocity is constant over time
WHy do car manufacturers try to avoid turbulent flow?
Turbulent flow increases the drag on a vehicle and so increases fuel consumption
What happens to the spring constant for two springs in series?
k is halved
What happens to the spring constant for 2 springs in parallel
k is doubled
What is the equation of youngs modulus in terms of force,area, extension and original length?
E = FL / AΔL
What does the difference in area between loading and unloading of a force-extension graph when the limit of proportionality has been passed but the elastic limit has not?
The energy lost as heat during loading and unloading
Explain the features of a Stress-strain graph that a ductile material will have?
It will have a large plastic region as it can be drawn into long wires, eg copper
Explain the features of a Stress-strain graph that a brittle material will have?
It will have a high Youngs Modulus (gradient) and no plastic region
How will the stress-strain graoh of a material with a high Young’s Modulus compare with that of a material with a lower one?
High YM will lead to a high gradient and vice versa
