Materials

Question 1

What is Density

Answer 1

Mass per unit volume

Question 2

What is the Density Equation

Answer 2

p = m/v

Density (kg m^-3) = Mass (kg) / Volume (m^3)

Question 3

What does Hooke’s Law state

Answer 3

Force is directly proportional to extension up to the limit of proportionality

Question 4

What is Directly Proportional

Answer 4

When two things increase by the same scale factor and go through the origin

Question 5

What is Hooke’s Law Equation

Answer 5

F = k Δl

Force (N) = Spring Constant or Stiffness (N m-1) x Extension (m)

Question 6

What is a Spring Constant or Force Constant

Answer 6

A measure of how hard it is bend or stretch a spring

Question 7

Describe the force-extension graph

Answer 7

Question 8

What does the area under a force-extension graph show

Answer 8

The elastic strain energy of the spring

Question 9

What is Elastic Strain Energy

Answer 9

Energy stored inside a stretched or compressed material

Question 10

What is Breaking Stress

Answer 10

The stress required to break a string

Question 11

What is the Elastic Strain Energy Equation

Answer 11

E = ½ FΔl

Elastic Strain Energy (J) = ½ x Force (N) x Extension (m)

Question 12

What is the Limit of Proportionality

Answer 12

When a spring no longer follows Hooke’s Law meaning the force is not directly proportional to extension up to the limit of proportionality

Question 13

What is the Elastic Limit

Answer 13

Just after the limit of proportionality were if you increase the load applied beyond this, the material will deform plastically

Question 14

What is Elastic Deformation

Answer 14

When a material returns to its original shape when the load is removed

Question 15

What is Plastic Deformation

Answer 15

When a material is permanently deformed and does not return to its original shape after the load is removed

Question 16

Describe Brittle and Plastic Materials

Answer 16

Brittle - when a material will extend very little, and therefore is likely to fracture (break apart) at a low extension

Plastic - when a material will experience a large amount of extension as the load is increased, especially beyond the elastic limit

Question 17

Describe the Force-Extension Graph for Brittle and Plastic Material

Answer 17

Question 18

Describe the force-extension graph for a streched material and explain why are the loading and unloading lines parallel

Answer 18

Because the material’s stiffness/ spring constant is constant

Question 19

Explain the Energy Behind Elastic and Plastic Materials

Answer 19

• When a stretch is elastic, all the work done is stored as elastic strain energy
• When a stretch is plastic, work is done to move atoms apart, so energy is not stored as elastic strain energy but is given off as heat

Question 20

Describe the Energy within a Spring when it is Stretched Vertically

Answer 20

• When a spring is hung vertically and stretched, kinetic energy is converted into elastic strain energy
• If it the force is removed, the elastic strain energy will be transferred back to kinetic energy (Conservation of energy)
• This kinetic energy is then transferred to gravitational potential energy as it rises

Question 21

What are some of the energy conservation issues for transport design

Answer 21

• Crash zones are desinged to plastically deform to decrease the car’s kinetic energy
• Seat belts stretch in order to convert some of the passenger’s kinetic energy into elastic strain energy

Question 22

What is Tensile Stress

Answer 22

Force per unit area of a material

Question 23

What is Tensile Strain

Answer 23

The ratio of extension to original length

Question 24

What is the Tensile Stress Equation

Answer 24

Stress = F/ A

Stress (Pa or N m-2) = Force (N) / Area (m2)

Question 25

What is the Tensile Strain Equation

Answer 25

Strain = Δl / l

Strain = Extension(m) / Length(m)

Question 26

What is the Young Modulus Equation

Answer 26

Young Modulus = (F/a) / (Δl/l)

Young Modulus (Pa or N m -2) = Stress (Pa or N m-2) / Strain

Question 27

Why do we use Young Modulus

Answer 27

So that the value will be the same regardless of the dimensions of the material being tested

Question 28

Describe the Young’s Modulus Graph and all of it’s components

Answer 28

Question 29

What is UTS (Ultimate Tensile Strength)

Answer 29

The max stress experienced before breaking

Question 30

Describe the Young’s Modulus Practical

Answer 30

• Set up the apparatus as shown in the diagram
• Measure the initial length of the test wire with the metre ruler
• Add a 1kg mass holder to both wires so they are taut and record the initial scale reading
• Add an additional 1kg mass to the test wire and record the new scale reading. Find the extension by subtracting the initial scale reading from the new scale reading and record it
• Add another 1kg mass and repeat this, adding 1kg each time up to around 8kg
• Repeat the experiment twice more and find and record the mean extension for each
• Measure the diameter of the test wire at various points along it using the micrometer and find and record the mean diameter
• Calculate the cross sectional area of the wire
• Find the force for each mass by using w = mg
• Plot a graph of Force against Extension and the young’s modulus will be the original length multiplied by the gradient and divided by the cross sectional area

Question 31

Explain why we use a comparison wire in the young’s modulus practical

Answer 31

• The comparison wire provides a reference point against which to measure the extension of the wire
• The comparison wire will be kept taut so by either using a spirit level and micrometer or a sliding vernier scale you can measure the extension more accurately
• The readings also made more accurate by making the original length of the test wire as long as possible, this reduces uncertainty in its measurement