Materials

Question 1

What is density?

Answer 1

the mass per unit volume of an object

Question 2

What is the equation to calculate density? Include units

Answer 2

P=m/v

where:
p= density (kgm^-3)
m= mass (kg)
v= volume (m^3)

Question 3

What does Hooke’s law state?

Answer 3

the extension of the material is directly proportional to the applied force (load) up to the limit of proportionality

Question 4

What is the equation for Hooke’s law?

Answer 4

F = kΔL

where:
F = force (N)
k = spring constant (N m^–1)
ΔL = extension (m)

Question 5

What is the spring constant? What does it measure?

Answer 5

-a property of the material being stretched
-measures the stiffness of a material

Question 6

What do we mean by the natural length?

Answer 6

the original length of a spring

Question 7

Draw the Hooke’s law graph, label all areas

Answer 7

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/Force-Extension-Graph.png

Question 8

What do we mean by the limit or proportionality?

Answer 8

the point beyond which Hooke’s law is no longer true when stretching a material

Question 9

What do we mean by the elastic limit?

Answer 9

the maximum amount a material can be stretched and still return to its original length

Question 10

What is the area under a force-extension graph?

Answer 10

the work done to extend a spring
or
elastic potential energy store

Question 11

How do we combine spring constants in parallel?

Answer 11

kTotal= k1 + k2 +k3…

Question 12

How do we combine spring constants in series?

Answer 12

1/kTotal= 1/k1 + 1/k2 +1/k3…..

Question 13

What does elastic behaviour mean?

Answer 13

regains shape after deformation

Question 14

What does plastic behaviour mean?

Answer 14

permanently deformed after extension
- doesn’t return to original length once load is removed

Question 15

What is tensile stress?

Answer 15

the force exerted per unit cross-sectional area of a material

Question 16

How can we work out tensile stress?

Answer 16

σ= F/A

where:
σ = tensile stress (Pa)
F = force applied (N)
A = cross-sectional area (m^2)

Question 17

What is tensile strain?

Answer 17

extension per unit length

Question 18

What do we mean by the ultimate tensile stress?

Answer 18

the maximum force per original cross-sectional area a wire is able to support until it breaks

Question 19

How can we work out tensile strain?

Answer 19

tensile strain= ΔL/L

where:
ΔL = extension (m)
L = original length (m)

Question 20

What is the area under stress-strain graph?

Answer 20

work done/volume

Question 21

What is yield stress?

Answer 21

the stress at which the material extends plastically when no or a small amount is added

Question 22

What is braking point?

Answer 22

-this is the maximum stress a material can stand before it breaks

Question 23

What do we mean by elastic region?

Answer 23

the region of the graph up till the elastic limit
-in this region, the material will return to its original shape when the applied force is removed

Question 24

What do we mean by plastic reigon?

Answer 24

the region of the graph after the elastic limit
-in this region, the material has deformed permanently and will not return to its original shape when the applied force is removed

Question 25

Draw a stress-strain graph labelling all areas

Answer 25

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/Stress-Strain-Graph.png

Question 26

What does it mean when a material is brittle?

Answer 26

very little to no plastic region
-the material breaks with little elastic and insignificant plastic deformation

Question 27

What does it mean when a material is ductile?

Answer 27

larger plastic region e.g. rubber, copper
-the material stretches into a new shape before breaking

Question 28

Draw and label the graph for loading and unloading a wire against force and extension

Answer 28

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/4.7.6-Loading-and-unloading-graph-1.png

Question 29

Draw and label the graph for loading and unloading a rubber band against force and extension

Answer 29

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/04/4.7.6-Loading-and-unloading-graph-2.png

Question 30

What do we mean by elastic (young’s) modulus?

Answer 30

a measure of stiffness
-material dependant

Question 31

How can we work out the young’s modulus of a material?

Answer 31

tensile stress/ tensile strain
or
(force x natural length)/(cross-sectional area x extension)

where:
F = force (N)
L = original length (m)
A = cross-sectional area (m^2)
ΔL = extension (m)
Young’s modulus (Pa)

Question 32

How can we calculate the young modulus from a stress-strain graph?

Answer 32

work out the gradient

Question 33

RP4: describe this practical

Answer 33

-aim of the experiment is to measure the young modulus of a metal in the form of a wire

-this requires a clamped horizontal wire over a pulley
- can also be done with a vertical wire attached to the ceiling with a mass attached

Question 34

RP4: How do you work out the young modulus from the measurements?

Answer 34

-if you have stress and strain, plot the graph and find the gradient

-if you have all values e.g. F, A, L etc., plot a graph of force against extension and multiply the gradient by natural length/ cross-sectional area

Question 35

What is the area of a stress-strain graph?

Answer 35

work done per unit volume