UNIT 1 - Solids Under Stress

Question 1

What is the limit of proportionality

Answer 1

the point at which the forces on an object are so intense that hookes law is no longer obeyed

Question 2

What is elastic limit

Answer 2

the maximum stress that can be applied to an object without deformation

Question 3

What is permanent extension?

Answer 3

There is a permanent, irreversible deformation

Question 4

What is elastic behavior

Answer 4

When the extension disappears when the forces is removed.

Question 5

What is plastic behaviour

Answer 5

When the extension decreases only slightly when the stress is removed. Doesn’t return to original size and shape

Question 6

What is spring constant

Answer 6

The force per unit extension

Question 7

What is stress and units

Answer 7

The force per unit cross-sectional area when equal opposing forces act on a body

Pa or Nm⁻ ²

Question 8

Define strain

Answer 8

The extension per unit length due to an applied stress

Question 9

Define Hooke’s law

Answer 9

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

Question 10

What is hooks law equation

Answer 10

F = kx
Force = spring constant x extension (from springs natural length)

Question 11

How to calculate ktotal (spring constant total)

Answer 11

K= f/x

For parallel
Ktotal = k1 + k2

For series
1/Ktotal = 1/k1 + 1/k2

Question 12

What happens to k if springs are put in series

Answer 12

X is doubled so k is halved

Question 13

What happens to k if springs are put in parallel

Answer 13

X is halved so k is doubled

Question 14

Unit for young modulus

Answer 14

Pascals
Pa

Question 15

Explain the term young modulus

Answer 15

Ratio of stress/strain

Question 16

Elastic def

Answer 16

A material that regains its shape after stresses are removed

Question 17

Ductile definition

Answer 17

Can easily be stretched or drawn into a wire

Question 18

Malleable

Answer 18

Can be hammered or pressed into a shape without breaking or cracking

Question 19

Brittle definition

Answer 19

Can snap without any yield

Question 20

Stiff definition

Answer 20

Small strains for large stressed, not stretchy or bendy (large young modulus)

Question 21

Plastic definition

Answer 21

Undergoes permanent deformation under large stress rather than cracking

Question 22

Strong definition

Answer 22

A large stress is needed to break it

Question 23

Hard definition

Answer 23

Resists indentation on impact

Question 24

What condition needed for young modulus to be calculated

Answer 24

When the work done is within the limit of proportionality

Question 25

What are the 3 broad categories of solids

Answer 25

Crystalline
Amorphous
Polymeric

Question 26

Explain what is crystalline solid and give 4 examples

Answer 26

Atoms are arranged into a crystal lattice which consists of regularly repeating unit cells. Crystalline solids exhibit long range order and symmetry.

Eg. Diamond, metals, graphite, salt

Question 27

Explain amorphous solids and 3 examples

Answer 27

Atoms have no long range order or symmetry. Considered to be super cooled liquid, atoms are randomly arranged with no overall pattern. More brittle and small elasticity.

Eg. Glass, Ice, Ceramics

Question 28

Explain polymeric solids and give 3 examples

Answer 28

Comprised of long molecular chains, usually containing carbon. Chains are randomly tangled up.

Eg. Rubber, cellulose, polyethylene

Question 29

What are the 4 parts on the line of a stress strain graph

Answer 29

Limit of proportionality- up until the stress and strain stop being proportional. (Young modulus)

Elastic limit - material can move up to elastic limit, and still return to original shape

Yield point - when u have such a stress u have a very large strain

Ultimate tensile strength (UTS) - the point where failure occurs