Topic 4: Materials Flashcards
What is density?
Density is the mass per unit volume of an object.
ρ=mv
What is upthrust?
Upthrust is the upward force acting on an object due to different pressures exerted on surface of object
What is Archimedes’ principle?
Upthrust is equal to the weight of object.
What is viscous drag?
Viscous drag is the
- frictional force between an object and fluid
- which opposes the motion between the object and the fluid.
What is Stoke’s Law formula?
F = 6πηrv
What are the conditions for Stoke’s Law formula to be used?
Object has to be:
- Small and spheric
- Low speed
- Laminar flow
- Terminal velocity
What is laminar flow?
Laminar flow is when the particles in a fluid
- Adjacent layers of fluid are parallel
- No abrupt changes in speed/direction
- Velocity at point is constant
What is turbulent flow?
Turbulent flow is when
- Layers of fluid cross into each other
- Edgy currents formed
- Streamlines no longer continuous
What is viscosity?
Viscosity is a measure of how easily a fluid flows.
High viscosity means fluid is thick. And resistant to flow.
How does viscosity change with temperature?
Liquids:
As temperature increases, viscosity of a liquid decreases.
Gases:
As temperature increases, the viscosity of a gas increases.
What is Hooke’s Law?
Hooke’s law states that extension of spring is directly proportional to the force applied.
ΔF = kΔx
What is stress and what are the 2 types?
Stress - Force applied per unit cross sectional area
Tensile force - pull on an object and extend it
Compressive forces - push onto an object to compress
σ = F/A
What is strain?
Strain is the extension per unit length
What is Young Modulus?
Young Modulus is measure of ability of a material to withstand changes in length with an added load
Young modulus is a value which describes stiffness of a material.
How can Hooke’s Law be illustrated?
Hooke’s law can be illustrated on a:
- Force-extension graphs
- Straight line when Hooke’s Law obeyed
Key features of Force-extension graph
Limit of proportionality
- Point beyond which Hooke’s Law is no longer obeyed; extension no longer proportional to applied force
Elastic limit
- After Elastic limit, object undergoes plastic deformation; will not return to original form
Yield Point
- Where material continues to stretch with minimal force applied to it.
What is elastic deformation?
Elastic deformation is when a material returns to its original shape once force applied is removed.
What is plastic deformation?
Plastic deformation is when material’s shape is changed permanently.
What do stress-strain graphs help indicate?
- Upto what stress/strain they obey Hooke’s Law
- Whether they exhibit elastic/plastic behaviour
- Value of Young Modulus
- Value of breaking stress
What is breaking stress?
Breaking stress is the value of stress which material will break apart.
What can the shape of a stress-strain graph show?
Brittle
- Material undergoes little to no plastic deformation before fracturing
Ductile
- can undergo large amount of plastic deformation before fracturing
Plastic
- Material will experience large amount of extension as the load is increased.
What is elastic strain energy?
Elastic strain energy is the work done on a material to stretch/compress it.
How can you calculate elastic strain energy?
Area under force extension graph
E = 1/2 FΔx
