Unit 1.5

Question 1

Hooke’s Law

Answer 1

The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great.

Question 2

Spring Constant, k

Answer 2

is the force per unit extension

Question 3

Hooke’s Law

Answer 3

The graph is a force-distance graph
Calculation- F=k*x
Gradient = an estimate of spring constant
Area under graph= the work done

Question 4

Hooke’s Law investigation

Answer 4

force-extension graph is used, points should go through origin.
Spring extension experiment, load weights on the spring record the extension.

Question 5

Strain, ε

Answer 5

is the extension per unit length

Question 6

Stress, σ

Answer 6

is the force per unit cross-sectional area

Question 7

Young Modulus, E

Answer 7

tensile stress divided over tensile strain

Question 8

Young Modulus Lab Book

Answer 8

Attach a known load to the end of the wire, measure the extension of the wire with a meter ruler.

Question 9

Elastic

Answer 9

describes a material that regains shape after stress is removed

Question 10

Ductile

Answer 10

Can be easily stretched or drawn into a wire

Question 11

Tough

Answer 11

Can absorb a great deal of energy before breaking

Question 12

Brittle

Answer 12

A material that would snap without yield

Question 13

Malleable

Answer 13

A material that can be hammered into shape

Question 14

Stiff

Answer 14

Small strains for large stresses

Question 15

Plastic

Answer 15

A material that undergoes permanent deformation under large stress rather than cracking

Question 16

Strong

Answer 16

Large stress needed to break it

Question 17

Hard

Answer 17

Resist indentation on impact

Question 18

Crystalline/Polycrystalline solids (metals)

Answer 18

Atoms arranged in ordered rows/layers. Can cause them to be ductile if bonds are weaker(dislocations occur)

Question 19

Why is a crystalline metal ductile?

Answer 19

Atoms are arranged in neat rows inside each crystal.
The crystals are not always in perfect rows, there are imperfections called edge dislocations.
When stressed the dislocations move, this is how plastic flow occurs.
This lowers stress needed to break the bonds, which causes them to be ductile.

Question 20

Strengthening Metals

Answer 20

1) Introducing foreign atoms, these hinder the movement of dislocations.
2) More grain boundaries, acts as an obstacle to dislocation movement. (Quench Hardening)
3) Other dislocations, additional dislocations move meet and obstruct each other’s progress.

Question 21

Ductile Fracture