Materials (4)

Question 1

Definition of density

Answer 1

Mass per unit volume of an object

Question 2

Units of density

Answer 2

kg per m cubed

Question 3

An object that’s more dense has more/less particles

Answer 3

More

Question 4

Volume of a sphere

Answer 4

4/3 pi r cubed

Question 5

volume of cube

Answer 5

d cubed

Question 6

volume of cylinder

Answer 6

pi r squared x height

Question 7

1mm cubed=

Answer 7

1 e-9 m cubed

Question 8

1cm cubed=

Answer 8

1e-6 m cubed

Question 9

Archimedes’ Principle

Answer 9

An object submerged in a fluid at rest has an upward buoyancy force (upthrust) equal to the weight of the fluid displaced by the object

Question 10

What happens when the weight of the fluid displaced is equal to the object’s weight

Answer 10

Object stops sinking

Question 11

When upthrust=weight…

Answer 11

Object floats

Question 12

How to calculate magnitude of upthrust

Answer 12

Find the volume of the submerged object, which is also the volume of the displaced fluid

Find the weight of the displaced fluid

Since m = ρV (density × volume), upthrust is equal to F = mg which is the weight of the fluid displaced by the object

Question 13

Equation for weight of displaced fluid

Answer 13

W=pVg

Question 14

What is viscous drag

Answer 14

the frictional force between an object and a fluid which opposes the motion between the object and the fluid

Question 15

Equation for Stoke’s law

Answer 15

F = 6πηrv

Question 16

What do the components of stokes law represent

Answer 16

F = viscous drag (N)

η = coefficient of viscosity of the fluid (N s m−2 or Pa s)

r = radius of the object (m)

v = velocity of the object (ms−1)

Question 17

Fluid with low viscosity is hard/easy to poor

Answer 17

Easy

Question 18

what is the viscosity coefficient

Answer 18

The coefficient of viscosity is a property of the fluid (at a given temperature) that indicates how much it will resist flow

Question 19

At terminal velocity, what forces are balanced (object in fluid) (2 equations)

Answer 19

W(sphere) = F(drag) + U
W(sphere =v(sphere)ρ(sphere)g

Question 20

Volume of displaced fluid is the same as…

Answer 20

Volume of the sphere in fluid

Question 21

Derive the equation for terminal velocity of a sphere in a fluid

Answer 21

v=(2π r^2 g (ps-pf))/9πη

Question 22

What are the conditions for stokes law (4)

Answer 22

The flow is laminar

The object is small

The object is spherical

Motion between the sphere and the fluid is at a slow speed

Question 23

What happens to layers of fluid in laminar flow

Answer 23

All layers moving in the same direction and don’t mix

Question 24

What happens to layers of fluid in turbulent flow

Answer 24

All layers move in different directions and mix

Question 25

How does viscosity change with temp (liquids and gases)

Answer 25

Liquids are less viscous as temperature increases Gases get more viscous as temperature increases

Question 26

When a force F is added to the bottom of a vertical metal wire, what happens

Answer 26

It stretches

Question 27

In materials that obey Hooke's law

Answer 27

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

Question 28

Hooke's law equation

Answer 28

ΔF = kΔx

Question 29

What happens to stiffness when spring's constant increases

Answer 29

It increases

Question 30

Extension of an object is _____ Compression of an object is _____

Answer 30

Extension=increase in length Compression=decrease in length

Question 31

Does the graph of F against x go through the origin

Answer 31

Yes

Question 32

What happens at the limit of proportionality and how is it shown on a Hooke's law graph

Answer 32

The point beyond which Hooke's law is no longer true when stretching a material i.e. the extension is no longer proportional to the applied force. The point is identified on the graph where the line starts to curve (flattens out)

Question 33

What happens at the elastic limit and how is it shown on a Hooke's law graph

Answer 33

The maximum amount a material can be stretched and still return to its original length (above which the material will no longer be elastic). This point is always after the limit of proportionality.

Question 34

Gradient of Hooke's law graph=

Answer 34

Spring constant

Question 35

Define stress

Answer 35

The applied force per unit cross sectional area of a material (could be tensile or compressive forces)

Question 36

Equation for stress

Answer 36

Stress=Force/area

Question 37

What is the ultimate tensile stress

Answer 37

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

Question 38

Define strain

Answer 38

The extension per unit length

Question 39

What is young's modulus

Answer 39

A measure of the ability of a material to withstand changes in length with an added load ie. how stiff a material is

Question 40

Young's modulus equation and unit

Answer 40

Stress/strain (Pa)

Question 41

When a material is elastic, stress and strain are ...

Answer 41

Directly proportional

Question 42

Gradient of stress/strain graph=

Answer 42

Young's modulus

Question 43

What is the yield point

Answer 43

Where the material continues to stretch even though no extra force is being applied to it

Question 44

Define elastic deformation

Answer 44

A change of shape where the material will return to its original shape when the load is removed

Question 45

Define plastic deformation

Answer 45

It is a change of shape where the material will not return to its original shape when the load is removed. Occurs after the yield point.

Question 46

What does stress/strain graph tell you (4)

Answer 46

Up to what stress and strain they obey Hooke's Law Whether they exhibit elastic and/or plastic behaviour The value of their Young Modulus The value of their breaking stress

Question 47

What is breaking stress

Answer 47

is the stress at the point where the material breaks

Question 48

How to remember order of points on a stress/strain or force/extension graph

Answer 48

Limit of proportionality Elastic limit Yield point LEY

Question 49

How to find elastic strain energy (or work done) on force/extension graph

Answer 49

Area underneath the graph

Question 50

How to find area under force/extension graph when a material doesn't obey Hooke's law

Answer 50

Split into shapes + count squares