meterials (everything) (flash cards made while going through book learning topic)

Question 1

what is density

Answer 1

mass per unit volume

Question 2

give density equaiton and units for each

Answer 2

p(kgm^-3)=m(kg)/v(m^-3)

Question 3

state hooks law

and give the equation

Answer 3

extension (ΔL) of a stretched object is proportionmal to the force (F) applied

F∝ΔL
therefore F=KΔL

dont forget about the reactionary force when drawing spring force diagra

Question 4

what is K in Hooks law when deeling with springs

Answer 4

the spring constent (the stiffness of an spring)

Question 5

1. what happens to a spring when a tensile
   or
2. compressive force acts on it.

Answer 5

1. the spring stretches as a result of a tensile force.
2. the spring squashes as a result of a comppressive force

Question 6

1. for a spring does K have the same value for compressive and tensile forces
2. does this apply to all materials

Answer 6

1. yes
2. no

Question 7

1. draw a force over-extension diagram and describe it
2. when force is released before the elastic limit is reached does the spring move back to its original position?
3. when force is released after the elastic limit is reached does the spring move back to its original position?
4. what is the area under the graph

Answer 7

1. look up graph
2. below the elastic limit the spring will contract to its original form.
3. after the elastic limit, the spring will no longer contract to its original shape after the load is released.
4. work done or if the elastic limit is not reached then the value of elastic strain energy as well

Question 8

when does hooks law stop working

Answer 8

when foce becomes too great and the limmit of proportionality is reached

Question 9

explain elastic deformation relative to the atoms within the material and why the original shape is kept after the load is released

Answer 9

a) when the meterial is put under tension, the atoms of the meterial are pulled apart from one another.

b) atoms can move small distences relative to there equalibrium positions, whithout actually changing position within the metarial

c) once load is removed, tha atoms return to there equalibrium distence apart.

Question 10

explain plastic deformation relative to the atoms within the meterial and why the original shape is not kept after tension is released

Answer 10

a)when the meterial is put under tension, the atoms of the meterial are pulled apart from one another.

b) some atoms in the material move position relative to one another

c) when the load is removed the atoms don’t return to their original positions

d) plastic deformation occourse - the meterial does not return to its original positions

Question 11

what happens when deformation is plastic

Answer 11

the meterial will not return back to its original shape (object is stratched past the elastic limit)

Question 12

what happens when deformation is elastic

Answer 12

the meterial will return back to its original shape (object is not stratched past the elastic limit)

Question 13

when a meterial is stretched, _______ has to be done in stretching the meterial

Answer 13

work

Question 14

1. what is enegy stored as during elastic deformation
2. when this force is removed stored enegy is…

Answer 14

1. elastic strain enegy within the meterial
2. transfered to other forms
   e.g an elastic namd is streted then fired across the room

Question 15

1. during plastic deformation work is done to _________ ______ and enegy is …

Answer 15

separate atoms

…not stored as strain enegy (its mostly disipated as thermal energy - think of blue stack heating up as it deforms)

Question 16

stress equation and units

Answer 16

stress = F/A Nm^-2 or Pa

Question 17

strain equation and units

Answer 17

strain = ΔL/L (no units, its just a ratio and is written as a number or percentage)

Question 18

does it matter for the stress and strain equations if the forces producing the stress or strain are tensile or compressive

Answer 18

no - the stress and strain equations work with both tensile and compressive forces

the only diffrence is you tend to think of tensile forcese as positive (+) and compressive forces as negetive(-)

Question 19

what is tensile stress on a meterial

Answer 19

force aplied on the meterial over and area

Question 20

what is tensile strain

Answer 20

the change in lenth of the meterial

Question 21

1. draw the stress over strain graph labelling importend points on the graph
2. explain the process of a material breaking as stress increases. go through all of the stages of the graph
3. what is the gradient of the graph (before the limit of proportionality)
4. what is the area under the stress over strain graph (before the limit of proportionality)

Answer 21

2. as stress increses the force pulling atoms apart form each other increses. the stress increses to the ultimate tensile stress point (UTS). eventually the stress becomes so great that the atoms seperate completly, and the meterial breaks. this is the braking stress point (B).
3. youngs modules
4. enegy stored in the meterial per unuit volume
   enegy per unit volume = 1/2 * stress * strain

Question 22

what is UTS

Answer 22

ulitimate tensile stress. it is the maximan stress a meterial can withstand.

Question 23

providong a meterial obeys hooks law what are the 2 equations for protential elastic strain enegy stored in the meterial

Answer 23

work done/E = 1/2 F * ΔL

subing in F=kΔL
E = 1/2 k * (ΔL)^2

Question 24

when is stress and strain proportional

Answer 24

up to the elastic limit

(seems like it should be up to the limit of proportionality but if you think about plastic deformation only happens after the elastic limit)

(don’t need to think about it too hard just remember enegy is stored a elastic strain enegy up until the elastic limit and therefore before the elastic limit the material bounces back to the original position)
(you are not really going to be asked specifics about the paired between P and E)

Question 25

young modulus equation and units

Answer 25

tensile stress / tensile strain

(F/A)/(ΔL/L)
=
FL/ΔLA

units = Nm^-2 ot Pa (same as stress since strain has no limits)

Question 26

1. what happens past the yeild point
2. draw a stress over strain graph including the yirld point

Answer 26

1. the meterial starts to stretch withought any load (large amount of plastic deformation takes place with a constent or reduced load)

2.look up or in revision book pg76

Question 27

stress over strain graph for a brittle meterial and lable

Question 28

stress over strain graph for a ductile meterial and lable

Question 29

stress over strain graph for a plastic meterial and lable

Question 30

1. draw a force over extension graph with a unloading line where the meterial passes the elastic limit
2. why is the unloading line parallel to the loading line
3. what is the area between the 2 lines

Answer 30

2. the stiffness K is the same (the forces between the atoms are the same as they were during the loading)
3. the work done to permently deform the wire

Question 31

strain equation

Answer 31

ΔL/L

Question 32

what is the pricible of moments

Answer 32

when a body is balenced:
total clocwise moment = total anti clockwise moment about a point