Materials

Question 1

Define density

Answer 1

Mass per unit volume

Question 2

Density equation

Answer 2

P=m/v

Question 3

Define Hookes law

Answer 3

The force applied is directly proportional to the extension up to the limit of proportionality

Question 4

What evidence is on a force against extension graph when Hookes law is obeyed

Answer 4

Straight line
Through origin

Question 5

Hookes law experiment

Answer 5

Measure original length of spring

Very load between 0 and 20N by attaching masses to the spring

Use at least 8 different masses covering that range

For each load measure extension produced with a ruler

Repeat measurements to spot and remove anomalies

Use set square to reduce parallax errors view at eye level when reading ruler

Plot force against extension graph

Question 6

Springs in parallel

Answer 6

Force is shared equally
Add spring constants

Eg 3 springs:
K=3k
△L=1/3△L

Question 7

Springs in series

Answer 7

Do not share force

Question 8

Elastic potential energy equations

Answer 8

EPE=(1/2)F△L

EPE=(1/2)K(△L)^2

Question 9

When would you use conservation of energy in an EPE problem?

Answer 9

Dynamic

Question 10

Stress equation

Answer 10

Stress= F/A

A=cross sectional area

Question 11

Stress units

Answer 11

Nm^-2
Pa

Question 12

Strain equation

Answer 12

Strain= △L / L

Question 13

Strain units

Answer 13

No units

Question 14

Difference between Young’s modulus and sprint constant

Answer 14

Young’s modulus is a measure of the stiffness of a material
Spring constant is a measure of a particular sample

Question 15

Young’s modulus equation

Answer 15

E= stress/strain

Question 16

How to find Young’s modulus from a force against extension graph

Answer 16

F=K△L

K= F / △L

E=FL/A△L

E= K x L/A

Question 17

Ductile material structure

Answer 17

Atoms can move around and reform bonds

This prevents cracks getting bigger and allows material to stretch

Question 18

Brittle material structure

Answer 18

Giant rigid structures made up of very strong bonds

Question 19

Brittle fracture

Answer 19

When stress applied tiny cracks focus the stress and get bigger
Until material breaks completely leaving a flat break

Question 20

Examples of brittle materials

Answer 20

Glass
China

Question 21

Examples of ductile materials

Answer 21

Metals
Rubber

Question 22

Brittle vs ductile

Answer 22

A brittle material will break without warning and leave flat surfaces

A ductile material will deform and stretch slowly before breaking leaving a deformed surface

Question 23

Define the limit of proportionality

Answer 23

The point beyond which the force applied is no longer directly proportional to the extension produced

Question 24

What feature of a graph shows the material is elastic?

Answer 24

No permanent extension

Question 25

Define tensile stress

Answer 25

Force per unit cross sectional area

Question 26

Define tensile strain

Answer 26

Extension per unit length

Question 27

Define elastic limit

Answer 27

The maximum force which can be applied without the wire being permanently deformed

Question 28

Why would an engineer need to consider yield stress when building something

Answer 28

Above the yield stress the building would behave plastically
This means it will deform due to small forced applied

Question 29

Define yield stress

Answer 29

The force per unit area
At which the material extends considerably