Summary Knowledge for Materials 1

49: be able to use the equation density = mass / volume.

Questions to answer:

- What is mass measured in?
- What does the prefix ‘k’ mean in front of a unit?
- What is the symbol for mass?
- What equation allows you to calculate weight given a mass?
- What units can volume be measured in?
- What is the symbol used to represent volume in an equation?
- How do you calculate the volume of a sphere?
- What is the value of Pi to three d.p?
- What does it mean if a unit has the prefix ‘m’?
- How do you convert between mm and m?
- How do you convert between mm3 and m3?
- What is the symbol for density?
- If the units of volume are mm3 and the units of mass are g, what will the units of density be?
- How do you convert g/cm3 to kg/m3?

Summary Knowledge for Materials 2

50: understand how to use the relationship upthrust = weight of fluid displaced

Questions to answer:

- What direction does the force weight act?
- What letter do we usually use to represent weight?
- What is the unit of force?
- What is the equation that links weight and mass?
- How would you calculate mass from volume and density?
- What does the term displacement mean in this context?
- What direction does the force of upthrust act?
- What is the definition of upthrust?
- How could you calculate upthrust if you had the volume of the object and the density of the fluid?
- What is the unit of force in SI base units?
- What can you say about the weight of an object and upthrust it experiences if the object is floating?

Summary Knowledge for Materials 3

51: a. be able to use the equation for viscous drag F = 6πηrv; b. understand that this equation applies only to small spherical objects moving at slow speeds with laminar flow) (or in the absence of turbulent flow) and that viscosity is temperature dependent.

Questions to answer:

- What is the unit of viscous drag?
- What does the symbol π mean in the formula for viscous drag?
- What does the symbol η mean in the formula for viscous drag?
- What does the symbol r mean in the formula for viscous drag?
- What does the symbol v mean in the formula for viscous drag?
- What is the unit for radius?
- What is the unit for velocity?
- How would you convert the unit for velocity from cm s-1 into m s-1?
- What is the unit for viscosity?
- In what direction does the viscous drag force act?
- What conditions are required to use the formula F = 6πηrv to calculate viscous drag?
- What is viscosity?
- What is the definition of laminar flow?
- What is the definition of turbulent flow?
- What is the relationship between viscosity and temperature?

Summary Knowledge for Materials 4

53: be able to use the Hooke’s Law equation, ΔF = kΔx, where k is the stiffness of the object.

55: a. be able to draw and interpret force-extension and force-compression graphs

b. understand the terms limit of proportionality, elastic limit, yield point, elastic deformation and plastic deformation and be able to apply them to these graphs

Questions to answer:

- What does the letter k stand for in the equation ΔF = kΔx?
- What does the letter x stand for in the equation ΔF = kΔx?
- What does the letter F stand for in the equation ΔF = kΔx?
- What does the symbol Δ stand for in the equation ΔF = kΔx?
- What does it mean to say that F and x are proportional?
- What are the conditions for a material to be said to be obeying Hooke’s Law?
- How could k be calculated from a graph of F vs x?
- What is the unit of the quality k?
- What is the unit of the quantify F?
- What is the unit of the quantity x?
- What would it mean if the value of x was negative?
- What does it mean if a material is under tension?
- What does it mean if an object is being compressed?
- What is the proportional limit?
- What is the elastic limit?
- What is the yield point?
- What is meant by plastic deformation?
- What is meant by elastic deformation?
- Draw a force-extension graph for a material and label the following: a. the limit of proportionality, b. the elastic limit, c. the yield point, d. the section where the material behaves elastically, e. the section where the material behaves plastically.
- Draw a force-extension graph for a material that has been stretched beyond it’s elastic limit and then had the load removed.

Summary Knowledge for Materials 5

54: understand how to use the relationships

- (tensile/compressive) stress = force / cross-sectional area
- (tensile/compressive) strain = change in length / original length
- Youngs modulus = stress / strain

56: be able to draw and interpret tensile/compressive stress-strain graphs, and understand the term breaking stress

Questions to answer:

- What are the symbol for stress, strain and Young’s modulus?
- What is the unit of stress?
- What is the symbol for cross sectional area?
- What is the unit for cross sectional area?
- What is the unit for strain?
- What is the unit for Young modulus?
- How would you convert mm2 into m2?
- What is the value of the prefix M in front of a unit?
- What is the value of the prefix μ in front of a unit?
- What is the unit Pa written in base SI units?
- Write a formula for Young’s Modulus in terms of force, cross sectional area, original length and change in length.
- What does the Young’s modulus tell you about a material?
- What is the ultimate stress?
- On a stress-strain graph which variable would go on the y-axis and which one on the x-axis?
- Draw a stress-strain graph for a material and label the following: a. the limit of proportionality, b. the elastic limit, c. the yield point, d. the section where the material behaves elastically, e. the section where the material behaves plastically.
- What does a steeper gradient on a stress-strain graph mean about the material?
- What is meant by the term breaking stress?

Summary Knowledge for Materials 6

58: be able to calculate the elastic strain energy Eel in a deformed material sample, using the equation ΔEel = ½FΔx, and from the area under the force/extension graph

The estimation of area and hence energy change for both linear and non-linear force/extension graphs is expected.

Questions to answer:

- What is the unit of elastic strain energy?
- What does it mean for a number to be written to 2 s.f?
- What does it mean for a relationship to be linear?
- When can the equation ΔEel = ½FΔx be used accurately to calculate elastic strain energy?
- What method can be used for calculating the area under a graph?
- What is calculated from the area underneath a force-extension graph?
- What is calculated from the area underneath a stress-strain graph?
- Why is the elastic energy of a material greater when a load is being added than when a load is being removed?