Materials Flashcards
What is the Density equation?
- Density = mass / volume
What does Upthrust equal?
Upthrust = Weight of fluid displaced
What is the Stokes Law equation?
F = 6πnrv
F = Force (N)
n = Coefficient of viscosity (Nsm-2)
r = Radius
v = Velocity
When does Stokes Law only apply?
- Only to small spherical objects moving at low speeds with laminar flow or absence of turbulent flow
What happens to the viscosity of most fluids as temp increases?
- Viscosity decreases
What is the Hookes Law equation?
- F = kx
- F = Force
- k = Stiffness or Spring constant
- x = Extension
What is the equation for Stress?
- Stress = Force / Cross sectional area
What is the equation for Strain?
- Strain = Change in length / Original length
- Strain = No unit
State the graph for a spring.
What is the Hookes Law Reigion?
- Where Force is directly proportional to x
What is the limit of proportionality?
- Point where Hookes law ceases to be obeyed
What is the Elastic limit?
- Point beyond which wire will not regain its original length when load is removed.
What is the yield point?
- The onset of plastic flow
What is plastic flow?
- Region where metal deforms extensivly and irreversibly hence plastically. If load is removed there would be little or no change in extension
State the graph for a rubber band.
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What is the equation for Youngs modulus?
- Youngs modulus = Stress / Strain
- Youngs modulus = Pa
- Stress = Pa
- Strain = No unit
What is the shape of a stress strain graph?
- Shape is the same as a force extension graph
- Youngs modulus can be found by the gradient of Hookes law region
- Ultimate tensile stress (UTS) is the maximum stress a material can bear before it breaks
How do you calculate elastic strain energy?
- Eel = 1/2 Fx
- You can also calculate this via area under force extension graph
- Area under a stress strain graph is the elastic strain energy per unit volume so to get elastic strain energy you multiply by volume
What is Hysterisis in rubber?
- Occurs when rubber band is loaded and unloaded
What does a Hysterisis in rubber graph look like?
What can we find from the Hysteresis graph?
- Elastic strain energy represented by area under loading curve
- Energy stored in rubber band is represented by area under unloading curve
- Increase in internal energy within rubber band during one loading and unloading cycle is equal to area enclosed in loop
State the difference between compresive and tensile stress?
- Compresive stress shortens an object
- Tensile stress streches the object
What is strength?
- Ability to withstand a large force/high breaking stress before breaking
What is stiffness
- Requires large forces for small deformations
What is ductile?
- Can be drawn or streched into wires
- Large plastic deformation before breaking
What is elastic
- Regains its original dimensions when a force is removed
What is plastic
- Extends extensivly and irreversibly
What is toughness?
- Ability to absorb energy from impacts without breaking
What is hardness?
- Difficult to indent surface
What is malluble?
- Can be hammered into thin sheets
What is the opposite of strong?
- Weak
What is the opposite to stiff?
- Flexible
Opposite to tough?
- Brittle
What is the opposite of elastic?
- Plastic
What is the opposite of hard?
- Soft
What is the opposite to ductile?
- Brittle
What is the opposite to malluble?
- Brittle
