Materials Flashcards
What is the density of a material
The density of a material is it’s mass per unit volume
State the equation used to calculate density
Density =mass/volume
What is the unit of density?
Kgm^-3
When an object is submerged in a fluid, what determines the upthrust it experiences
The upthrust of a submerged object is equal to the weight of the fluid displaced
What determines whether an object floats or sinks
The balance between the weight and upthrust of the object. If the weight exceeds the upthrust, the object will sink
Why will a uniform object with a density greater than that of a liquid it is submerged in always sink
-the upthrust of the object will be equal to the weight of the of the liquid displaced
-therefore there maximum upthrust will be equal to the density of the fluid x volume of object x gravitational field
What shaped object does stokes’ law apply to?
Stokes’ law only applies to small spherical objects
What type of flow is required for stokes’ law to apply?
Laminar
What does stokes’ law allow you to calculate
The viscous drag force that a small spherical object experiences when falling at low speeds through a viscous fluid with laminar flow
State the stokes’ law equation
F=6πnrv
n=viscosity
r=radius of sphere
v=speed of sphere
What is elastic deformation
An object has undergone elastic deformation if it returns to its original shape once the deforming force is removed
What is plastic deformation
An object has undergone plastic deformation of it no longer returns to its original shape once the deforming forces are removed. It will have permanent deformation
Express hooke’s law in words
The extension of an elastic object is directly proportional to the force that is applied to it, up to its limit of proportionality
What is the limit of proportionality
The point beyond which the force and extension will no longer be directly proportional to each other - hooke’s law is no longer obeyed
What is the elastic limit
The point beyond which the object will no longer elastically deform, and will instead deform plasticslly
State the defining equation of hooke’s law
F=kx
What is mechanical stress
The force experienced by an object per unit area
State the equation for stress
Stress=F/A
What is the unit of stress
Nm^-1
State the equation for strain
Strain=x/L
What is the unit of strain
Strain is unitless
What does the young modulus of a material tell you
A materials young modulus is a measure of how much force is required for a given extension, regardless of the objects dimensions
What equation is used to calculate a materials young modulus
YM=stress/strain
What unit is used for the young modulus of a material
Nm^-2
What is breaking stress
Breaking stress is the maximum stress that an object can withstand before fracturing
What is the yield point?
The point which the object will experience a large extension without substantial increase in the force applied
What type of energy is stored in an object that has been stretched
Elastic potential energy
State two equations used to calculate the energy stored in a spring
E=1/2 Fx
E=1/2 kx^2
What does the gradient and area represent on a force-extension graph
-the gradient represents the elastic constant (k)
-the area represents the Aston potential energy stored in the spring
