Materials Flashcards
Use the definitions of laminar and turbulent flow to describe the differences between them.
Laminar flow: no abrupt changes in direction or speed of flow
Layers don’t mix
Turbulent flow: abrupt changes in direction or speed of flow
Layers mix
State the 3 conditions for Stokes’ law referring to size/ shape of object, speed of object and type of flow. State what F represents.
- Small, spherical objects
- Travelling at low speeds
- With laminar flow
- F represents viscous drag
Describe the conditions when a rising object is travelling at constant velocity. Include a word equation and name this velocity.
Forces are balanced
Weight + Viscous drag = Upthrust
Terminal velocity
State what upthrust is equivalent to. Give a word equation for upthrust in terms of density and volume.
Upthrust is equal to the weight of displaced fluid
Upthrust= density of fluid x volume of submerged object x 9.81
State how the viscosity of a gas and a liquid varies as temperature is increased.
Liquids get less viscous
Gases get more viscous
State Hooke’s law and the corresponding equation.
F=kx
An object obeys Hooke’s law if its extension/ compression is directly proportional to the load/ force applies to it up to the limit of proportionality
Describe force extension graph for an object that obeys Hooke’s law.
Straight line graph
through the origin
Springs obey Hooke’s law. What are the pairs of equal and opposite forces for springs in tension and springs in compression?
Tension- tensile force in spring and tensile force stretching spring
Compression- compressive force in spring and compressive force smashing spring
Explain in terms of force how overall extension varies for 2 springs in parallel and 2 springs in series compared to a single spring.
Parallel- force in each spring is halved so overall extension is halved
Series- force in each spring is the same so overall extension is doubled
Explain what is meant by elastic deformation and what happens to an elastic material under tension in terms of atoms.
If a deformation is elastic, the material returns to its original shape/ dimensions once the forces are removed
When the material is put under tension, the atoms in the material are pulled apart form one another and move slightly relative to their equilibrium position
The atoms don’t change position in the material so once the load is removed, the atoms return to their equilibrium positions
Explain what is meant by plastic deformation and what happens to a plastic material under tension in terms of atoms.
If a deformation is plastic, the material is permanently deformed
When the material is put under tension, some atoms move position relative to each other
When the load is removed, the atoms don’t return to their original positions
State what is represented by the area between the unloading line and the curve.
Work done to permanently deform the object.
Explain why using Young Modulus is better for comparing how much different samples stretch than force-extension/ Hooke’s law.
How much a material stretches for a particular applied force depends on its dimensions/ size
Stress/ strain is unaffected by the size of the sample
Hooke’s law applies to an object rather than a material so is different for different materials/ sizes
Describe what happens at the breaking stress in terms of atoms. State what breaking stress and ultimate tensile stress depend on.
Stress causes atoms to pull apart from each other
At the breaking stress the atoms separate completely
Breaking stress and UTS depend on conditions like temeprature
Describe Young Modulus E in terms of how it relates stress and strain, what it measures, why it is a property of a material and how to calculate it from a stress/ strain curve.
YM is the constant of proportionality between stress and strain up to the limit of proportionality
YM is a measure of stiffness of a material
Property of a material because it is unaffected by shape/ size/ dimensions of object
E= gradient of straight line part of curve from origin to limit of proportionality
