Materials

Question 1

Define DENSITY

Answer 1

The mass per unit volume of a material

Question 2

Equation for DENSITY?

Answer 2

Density (kgm^-30= Mass(kg)/Volume(m^3)

D=M
—–
V

Question 3

Characteristics of DENSITY

Answer 3

Density does not vary with size or shape, depends on material only

Question 4

Define HOOKE’S LAW

Answer 4

The extension of a material is directly proportional to the force applied to it until the limit or proportionality is reached

Question 5

Equation for HOOKE’S LAW?

Answer 5

Force(N)=spring constant(Nm^-1) x extension (m)

F = KX

Question 6

What is directly proportional in HOOKE’S LAW?

Answer 6

Extension and Force applied

Question 7

What does a tensile force do to a spring?

Answer 7

Stretch the spring

Question 8

What does a compressive force do to a spring?

Answer 8

Compress the spring

Question 9

When is the limit of proportionality broken?

Answer 9

As soon as the graph begins to curve

Question 10

What is the point called when the graph just begins to curve on a force - extension graph?

Answer 10

The elastic limit

Question 11

What happens if you continue to apply force beyond the elastic limit?

Answer 11

The material will become permanently stretched and will be longer than before the force was applied.

Question 12

What is it called when the material is stretched to a point it will no longer return to original length?

Answer 12

Plastic deformation

Question 13

Think of a practical to investigate extension of a material

Answer 13

1. Get a ruler, clamp, clamp stand, material and 1kg of weights
2. Set up equipment so weights are hanging off of the material you are testing and the ruler is up against the clamp stand
3. Measure original length before adding additional weight.
4. When original weight measured increase the weights by 100g and record new length
5. Do this until all weights are used.
6. Then unload and record lengths per 100g you take back off
7. Plot a graph of force against extension

Question 14

What is elastic deformation?

Answer 14

The material returns to its original state when the force is removed

Question 15

What happens in terms of the atoms of the material in elastic deformation?

Answer 15

When under tension the atoms are pulled part form one another. They can move small distances from their equilibrium without changing position in the material. When un-loaded the atoms return to their point of equilibrium

Question 16

Define STRESS

Answer 16

Force applied per unit cross-sectional area

Question 17

Equation for STRESS

Answer 17

Stress(Pa or Nm^-2) = force(N)/cross sectional area(m^2)

sigma = F
————
A

Question 18

Define STRAIN

Answer 18

Extension per unit length before extension

Question 19

Equation for STRAIN

Answer 19

Strain = extension(m)/original length(m)

Large curly E = Delta L
——————
L

Question 20

When calculating is a tensile force +ve and a compressive force -ve?

Answer 20

YES

Question 21

What does UTS stand for?

Answer 21

Ultimate Tensile Strength

Question 22

What is UTS?

Answer 22

The maximum stress a material can withstand

Question 23

Where is point of UTS on a stress - strain graph?

Answer 23

When the gradient is no longer +ve or zero

Question 24

What is breaking stress?

Answer 24

When the atoms of a material actually break away from each other causing the material to break

Question 25

Where on the stress-strain graph is breaking stress?

Answer 25

At the end of the graph

Question 26

What is elastic strain energy?

Answer 26

The energy required or work done to stretch a material and is stored as potential energy

Question 27

How would you calculate the strain energy on a graph?

Answer 27

Find the area underneath a force - extension graph

Question 28

What is the Young’s Modulus a measure of?

Answer 28

The stiffness of a material

Question 29

Equation for YOUNG’S MODULUS

Answer 29

YM= tensile stress/tensile strain

E(Pa or Nm^-2)= Sigma
————–
Big Curly E

Question 30

Define YOUNG’S MODULUS

Answer 30

A constant for the linear relationship of a material between tensile stress and strain

Question 31

Prepare an experiment to determine the Young’s Modulus of a piece of steel wire

Answer 31

1. Get a long thin piece of test wire as is possible
2. Find the cross-sectional area of the wire using a micrometer in several place along the wire and make an average assume the wire is circular
3. Clamp the wire to a bench and put weights on the end of the wire so that it takes the slack then measure the length of the unstretched wire
4. Increase the weights and take measurements every increase in weight
5. Use results to plot a stress-strain graph and then find the gradient of the straight part to calculate the Young’s Modulus

Question 32

What is the yield point?

Answer 32

The point when the material stretches without much extra force being required (large amount of plastic deformation - Can be shown on a stress-strain graph by the curves gradient being very close or almost zero

Question 33

What is the difference between a force - extension and stress - strain graph

Answer 33

Force - Extension shows the force and extension relationship for a specific object that is being tested

Stress- Strain shows the material in generals relationship

Question 34

If a metal wire is plastically deformed, when unloaded what will happen?

Answer 34

The gradient of the unloading will be the same as the loading gradient when it was elastically deformed (parallel to each other)

Question 35

Features of a brittle material?

Answer 35

On a stress - strain graph the material will have a very sharp curve at the end or no curve at all when it reaches its breaking stress

There are strong bonds between brittle materials but the atoms are all facing different directions, so when the force is applied atoms can’t move to bend with the material