materials Flashcards
density
p=m/v, mass per unit volume
upthrust
the weight of fluid displaced
why do objects submerged in a fluid experience upthrust
the fluid which is displaced wants to take up the volume. if it is floating, weight=upthrust.
stokes law
F=6rvnπ, used to calculate viscous drag
viscous drag
the resistive force experienced by an object moving in fluid
conditions for stokes law
-object is small and spherical
-object moves at low speed with laminar flow
laminar flow
the particles in a fluid move by following smooth paths with little to no mixing between adjacent layers of the fluid
turbulent flow
the particles in the fluid mix between layers and form separate currents. often described as chaotic
viscosity
measure of how resistant a fluid is to deformation. determined by the internal friction forces that occur between adjacent layers of the fluid. viscosity is temperature dependent
hookes law
extension is directly proportional to the force applied, given that environmental conditions are kept constant
∆F=k∆x
Youngs modulus
value which describes the stiffness of a material
YM=stress/strain
strain
caused by stress, change in length over the original length
strain=∆x/x
force extension graph
shows how extension varies with force, hookes law can be demonstrated by a straight Lin through the origin, directly proportional.
stress
force applied per unit cross-sectional area
stress=F/A
what is point p on a force extension graph
limit of proportionality, after this point hookes law is mot obeyed
what is point e on a force extension graph
elastic limit, after this point the material will not return to its original shape and undergo plastic deformation
what is point y on a force extension graph
yield point, where extension starts to increase with no increase in load
how is energy lost in plastic deformation
work is done to move atoms apart, so energy is dissipated as heat
stress-strain graphs
describe the behaviour of a material
ductile
can undergo large amounts of plastic deformation before fracturing
brittle
material undergo little to no plastic deformation before fracturing
plastic
experiences a large amount of extension as load is increased
breaking stress
value of stress at which the material will break apart, this value will depend on the conditions of the material eg. its temperature
elastic strain energy
when work is done on a material to stretch or compress it, this energy is stored as elastic strain energy, it can be found by finding the area under a force extension graph or using the formula ∆E=0.5F∆x
spring in ‘series’
extension is doubled
springs in ‘parallel’
extension is halved
