Topic 4 - Materials

Question 1

density =

Answer 1

mass / volume

Question 2

archimedes pricipal is…

Answer 2

upthrust = weight of fluid displaced

Question 3

fluid

Answer 3

a substance that can flow

Question 4

density

Answer 4

is a measure of the mass per unit volume of a substance.

Question 5

upthrust

Answer 5

is an upwards force on an object caused by the object displacing fluid

Question 6

hydrometer

Answer 6

is an instrument used to determine the density of a fluid

Question 7

when is viscous drag exerted?

Answer 7

when an object is in laminar flow

Question 8

what does viscous drag depend on?

Answer 8

vicousity of fluid
speed of body
surface area

Question 9

mass

Answer 9

the amount of matter in an object

Question 10

Viscous drag

Answer 10

a resistive force acting on an object travelling through a fluid

Question 11

stokes law

Answer 11

F = 6πrηv

Question 12

units of coefficiant of viscosity, η

Answer 12

Nm^-2s or Pas

Question 13

What does stokes law apply to

Answer 13

small spherical objects travellling at slow speeds with laminar flow

Question 14

viscosity equation proof proof steps.

Answer 14

1. sum of forces W = U + F
2. W = m(s)g, U = m(f)g, F = 6πrηv
3. m=ρV
4. V = 4/3πr^3
5. cancel like terms in each expression
6. rearrange for η

Question 15

uses for stokes law

Answer 15

alcohol testing, food, sports, car design, medicine, comestics

Question 16

How to measure the volume of irregular objects

Answer 16

measure how much water it displaces

Question 17

upthrust is…

Answer 17

weight of fluid displaced

Question 18

Laminar flow properties

Answer 18

• streamlines

- no mixing of layers

Question 19

Turbulent flow properties

Answer 19

• dissapation of energy
• eddy currents
• mixing of layers

Question 20

What forces act when a material is stretched

Answer 20

• the stretching force

- interatomic forces

Question 21

Hookes law

Answer 21

the force is directly proportional to the extension (and compression)
F = kx

Question 22

Gradient of a force extension graph

Answer 22

the stiffness

Question 23

limit of proportionality on a force extension graph

Answer 23

where the gradient stops being constant

Question 24

yield point on a force extension graph

Answer 24

where the gradient levels out

Question 25

elastic limit on a force extension graph

Answer 25

between the limit of proportionality and yield point

Question 26

breaking point on a force extension graph

Answer 26

where the gradient drops off at the end

Question 27

elastic deformation

Answer 27

material returns to its original shape once the deforming force has been removed

Question 28

plastic deformation

Answer 28

material does not return to its original shape once the deforming force ha been removed

Question 29

yield point

Answer 29

Where there is a large increase in extension for a small increase in force

Question 30

The steeper the gradient of a force extension graph...

Answer 30

the stiffer the object

Question 31

elastic potential energy

Answer 31

the work done to stretch a spring

Question 32

calculate elastic potential energy from a force extension graph

Answer 32

area underneath the graph (up to the limit of proportionality)

Question 33

elastic potential energy =

Answer 33

= 1/2Fx

Question 34

properties of materials

Answer 34

- stiff/flexible - elastic/plastic - ductile/malleable - tough/brittle

Question 35

felxible

Answer 35

small force for large extension

Question 36

ductile

Answer 36

can be drawn into wires, Produces a large plastic deformation under tension.

Question 37

malleable

Answer 37

can be hammered into shape

Question 38

tough

Answer 38

absorbs a lot of energy before they snap

Question 39

brittle

Answer 39

can't absorb energy, the crack/shatter immediately

Question 40

How does area effect how much a wire stretches

Answer 40

- thin wires stretch more | - thick wires stretch less

Question 41

tensile stress =

Answer 41

= force/area

Question 42

stress unit

Answer 42

Pascal

Question 43

difference between stress and pressure

Answer 43

- stress only happens to solids | - pressure applies to a surface stress occur throughout the solid

Question 44

Ultimate tensile stress

Answer 44

the measure of strength. Its the stress when a material breaks or yields.

Question 45

Tensile strain =

Answer 45

extension / original length

Question 46

unit of strain

Answer 46

no unit (its a ratio/ fraction)

Question 47

young modulus =

Answer 47

stress/strain

Question 48

young modulus

Answer 48

a property of a material that measures how difficult it is to change the shape of a material

Question 49

young modulus unit

Answer 49

Pascals

Question 50

find the young modulus experiment

Answer 50

1. measure the diameter of the wire. Measure the original length of the wire. 2. attach the wire to the desk and thread it over a pulley with hanging masses on the end. Put a sticky label on the wire at the end of the metre ruler. 3. Add the masses to the hanger and record the distance movement of the sticky marker. 4. plot extension against the weight (mg). The gradient is equal to length/area*young modulus.

Question 51

area under stress strain graph

Answer 51

the energy stored per unit volume

Question 52

hard

Answer 52

resistant to indentation/scratching Or surface is resistant to plastic deformation

Question 53

stiff

Answer 53

large force for small extension

Question 54

high tensile strength

Answer 54

undergo a large stress/force before breaking.

Question 55

linear relationship

Answer 55

increase in x is constant for fixed increases in y

Question 56

what happens wire a wire passes its limit of proportionality

Answer 56

there is a large increase in extension for a small increase in mass. It will no longer return to its original shape as it has been plastically deformed.

Question 57

how to make extension more accurate (5)

Answer 57

- use a pointer on the wire/ masses to make it easier to read - read at eye level to avoid parallax - use a set square to ensure the rulers vertical - wait for extension to finish - add masses gently

Question 58

laminar flow

Answer 58

where the layers of flow are parallel and do not mix/cross, no abrupt change in speed or direction of flow.

Question 59

turbulent flow

Answer 59

where the layers of flow mix forming eddy currents and causing energy to be dissipated. Random changes in speed or direction.

Question 60

F in stokes law

Answer 60

viscous drag

Question 61

spring constants in parallel

Answer 61

Kt = K1 + K2

Question 62

spring constants in series

Answer 62

1/Kt = 1/K1 + 1/K2

Question 63

viscosity equation

Answer 63

(2gr^2 (ρs - ρf))/9v

Question 64

finding drag on an object

Answer 64

drag = +- upthrust +- weight | measure radius + mass of object & use known densities

Question 65

area under stress strain graph

Answer 65

toughness (energy it can absorb before it snaps)

Question 66

compressive strain vs tensile strain

Answer 66

compression decreases in length tensile increases in length