4 Materials Flashcards
Equation for density
p=m/v
Density=mass/volume
Equation for pressure in a fluid (learn)
P=hpg
Pressure=height x density x gravity
What is upthrust equal to?
The weight of the fluid displaced
U= mg of fluid displaced
Cohesive
Forces of neighbouring molecules in the fluid
Adhesive
Forces of the surfaces of solids (obstacles/walls of pipe)
Laminar
When particles don’t cross over each other (streamlined)
Turbulent
When particles do cross over each other
Eddy currents/ vortices
When the fluid swirls around and is turbulent
When can Stokes law be used?
When a small spherical ball is falling through a fluid in which the flow of the fluid is laminar
Stokes law
F=6 x pi x n x r x v
F=viscous drag
n=the coefficient of viscosity
r=radius of sphere
v= velocity
Hookes law
k= F/x
Limit of proportionality
The point where hookes law ceases to be obeyed
Elastic limit
When the load is removed, spring will no longer take original shape
Yield point
The onset of plastic flow
Elastic behaviour
When a force is exerted the bonds holding the atoms together are stretched
Plastic flow
When a force is exerted the layers of atoms slide over each other and can’t return
What happens to polymers when a force is applied?
Polymers have long chain molecules which are tangled. When a force is applied they untangle and there is a large extension. Then the bond becomes harder to stretch once they are untangled
Young’s modulus
E=stress/strain
Equation for stress
Stress= force/area
Equation for strain
Strain= extension/ original length
What is true when stress strain graphs are proportional?
The gradient is proportional
Strong
High breaking stress
Hardness
How difficult it is to indent the surface
Stiffness
The gradient of a force extension graph
Toughness
The energy density up to fracturing
Elastic
Regains original shape when force is removed
Ductile
Can be drawn into wires
Malleable
Can be hammered into thin sheets
Elastic strain energy
Elastic strain energy= force x extension
How can elastic strain energy be found on a force extension graph
Area under graph
A=1/2Fx
A=1/2kx^2
What is the gap between the loading and unloading curve in a hysteresis in rubber?
Energy lost as thermal energy
Strength
Stress needed to break
With reference to the stress strain graph, why are ductile materials suitable for the production of wires
They have a large region of plastic deformation
