Studied by 6 peoplearchimedes’ principle
states that the upthrust experienced by an object is equal to the weight of the fluid it displaces
upthrust=
weight of fluid displaced
how can the weight of displaced fluid be calculated?
by finding the product of the density and volume of displaced fluid, multiplied by gravitational field strength
formula for upthrust
pVg
what is the volume of the displaced fluid for a fully submerged object?
volume of the object
what is viscous drag force?
resistive force experienced by an object moving in a fluid
what is the term for the resistive force experienced by an object moving in fluid?
viscous drag force
what can be used to calculate viscous drag force exerted on an object?
Stoke’s law
what are the conditions for Stoke’s law?
the object must be small and spherical, and moves slowly with laminar flow
what is the equation for stoke’s law?
6 x pi x viscosity x radius x terminal velocity
what is laminar flow?
where particles flow by following smooth paths with little to no mixing between layers of path
what is turbulent flow?
where particles mix between layers of path and form separate currents
what is viscosity?
a measure of how resistant a fluid is to deformation, for example caused by an object moving through it
what is a fluid’s viscosity determined by?
the internal frictional forces occurring between adjacent layers of fluid
what variable affects viscosity?
temperature
what is the effect of temperature on the viscosity of most liquids?
as temperature increases, the viscosity of a liquid decreases
what is the effect of temperature on the viscosity of a gas?
as temperature increases, the viscosity increases
why are the effects of temperature on viscosity of liquids and gasses different?
frictional forces between layers are formed by different means
what does Hooke’s law state?
extension is directly proportional to the force applied
what are the conditions of Hooke’s law?
external conditions, such as temperature, remain constant
what is the equation for Hooke’s law?
stiffness x change in length (extension)
what is stress?
force applied per unit cross sectional area
what is the formula for stress?
force/area
what is the unit of stress?
Pa or Nm^-2
what is strain?
change in length over the original length
what is the formula for strain?
extension/length
what is the relationship between stress and strain?
for a material which obeys Hooke’s law, stress is proportional to strain
what can be said about the relationship between stress and strain?
the value of stress/strain is constant
what is the value of stress/strain equal to?
Young Modulus
what is young modulus?
a value which describes the stiffness of a material
what is the derived formula for Young Modulus?
(force x length)/(area x extension)
what is the limit of proportionality?
point after which Hooke’s law is no longer obeyed
what is the elastic limit?
point just after the limit of proportionality
what happens if you increase the force applied beyond the elastic limit?
the material will deform plastically
what is the yield point?
point at which material begins to stretch without an increase on the load
what is elastic deformation?
where a material returns to its original shape once the applied force is removed
why does elastic deformation occur?
as all the work done is stored as elastic strain energy
what is plastic deformation?
where a materials shape is changed permanently
why does plastic deformation occur?
as work is done to move atoms apart, so energy is not only stored as elastic strain energy, but also dissipated as heat
what do force-compression graphs show?
how the compression of an object varies with the force applied to it
why do force-extention and force-compression graphs often look very similar?
solids often behave similarly when tensile and compressive forces are applied
what is the key difference between force-extention and force-compression graphs?
beyond the elastic limit, compressed solids will suddenly change shape and break as opposed to extending plastically
what is a stress-strain graph?
graph describing the behaviour of a material
how does a stress-strain graph differ from a force-extension graph?
they describe behaviour of a material rather than specific object
what can the shape of a stress-strain graph show?
whether a material is ductile, brittle or plastic
what is a ductile material?
a material that can undergo a large amount of plastic deformation before fracturing
what is a brittle material?
a material undergoes little to no plastic deformation before fracturing
what is a plastic material?
a material which experiences a large amount of extension as the load is increased
what is the breaking stress?
the value of stress at which the material will break apart
what does the breaking stress depend on?
dependant on the conditions of the material for example the temperature
what is elastic strain energy?
energy stored when work is done to deform a material
how can the elastic strain energy be found from a graph?
area under a force-extension graph
why can elastic strain energy not be calculated by formula W=F#s?
as the force is variable not constant
what formula can be used to calculate elastic strain energy?
(force x extension)/2
what is shown on a force - extension graph once a material is stretched past its elastic limit?
the graph showing loading and unloading lines will not return to the origin
what can be said about the loading and unloading lines on the force/extension graph? Why?
the loading and unloading lines will be parallel as the material's stiffness remains constant
how can the work done to permanently deform the material be found from a force-extension graph?
from the area between the loading and unloading line
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