04 Materials

Question 1

Accuracy definition

Answer 1

How close you are to the true value

Question 2

Sensitivity definition

Answer 2

How small a division a piece of equipment can measure to

Question 3

Precision

Answer 3

How similar repeated values are

Question 4

What causes upthrust

Answer 4

Caused by the displacement of water

Question 5

When an object is submerged in a fluid, what determines the upthrust experienced?

Answer 5

The upthrust of a submerged object is equal to the weight of the fluid that it displaces

Question 6

How to calculate upthrust (equation)

Answer 6

Density of fluid x volume in water x acceleration due to gravity (9.81)

Question 7

What determines whether an object floats or sinks?

Answer 7

The balance between the weight and the upthrust of the object. If the weight exceeds the upthrust, the object will sink

Question 8

Why will a uniform object, with a density greater than that of the liquid, it is submerged in, always sink

Answer 8

• the upthrust of the object will be equal to the weight of the fluid displaced
• therefore, the maximum upthrust will be equal to the density of the fluid x volume of object x gravitational field strength
• the weight of the object is equal to the density of the object x volume of object x gravitational field strength
• if the objects density is greater, the weight will always be greater than the upthrust and the object will sink

Question 9

What shaped objects does stokes’ law apply to?

Answer 9

Stokes’ law only applies to small spherical objects

Question 10

What type of flow is required for Stokes’ law to apply

Answer 10

Laminar flow

Question 11

What does Stokes’ Law allow you to calculate

Answer 11

The viscous drag force that a small spherical object experiences when falling at low speeds through a viscous fluid with Laminar flow

Question 12

Stokes’ Law equation

Answer 12

F=6πηrv
η= the viscosity of the fluid
r= the radius of the sphere
v = the velocity of the sphere
F= frictional force acting on the interface between the fluid and the particle.

Question 13

What’s elastic deformation

Answer 13

An object has undergone elastic deformation if it returns to its original shape once the deforming forces are removed

Question 14

What is plastic deformation

Answer 14

An object has undergone plastic deformation if it no longer returns to its original shape once the deforming forces are removed. It will have permanent deformation

Question 15

Express Hooke’s Law in words

Answer 15

The extension of an elastic object is directly proportional to the force that is applied to it, up to its limit of proportionality

Question 16

What is the limit of proportionality

Answer 16

The point beyond which the force and the extension will no longer be directly proportional to each other - Hooke’s Law is no longer obeyed

Question 17

What is the elastic limit

Answer 17

The point beyond which the object will no longer elastically deform, and will instead deform plastically

Question 18

State the defining equation for Hooke’s law

Answer 18

F = kΔx
F= force applied (N)
K= stiffness constant
Δx = extension (m)

Question 19

What is mechanical stress

Answer 19

The force experienced by an object per unit area

Question 20

State the equation for stress

Answer 20

Stress = F / A
F = the force applied
A = the cross-sectional area

Question 21

What is the unit for stress

Answer 21

Nm^-2

Question 22

State the equation for strain

Answer 22

ΔL / L

ΔL = the change in length
L = original length

Question 23

What is the unit for strain

Answer 23

Strain is a unitless quantity because it is the ratio of 2 lengths

Question 24

What does the Young Modulus of a material tell you

Answer 24

A material’s Young Modulus is a measure of how much force is required for a given extension, regardless of the objects dimensions

Question 25

What equation is used to calculate a materials Young Modulus

Answer 25

Young Modulus = stress / strain Which is the gradient of the stress strain graph with strain on the x axis and stress on the y axis

Question 26

What unit is used for a materials Young Modulus

Answer 26

Nm^-2

Question 27

What is breaking stress

Answer 27

Breaking stress is the maximum stress an object can withstand before fracturing

Question 28

What is the yield point

Answer 28

The point beyond which the object will experience a large extension without substantial increase in the force applied The point at which the amount of stress the material is at causes the wire to begin to plastically the deform

Question 29

What type of energy is stored in an object that has been stretched

Answer 29

Elastic potential energy

Question 30

State 2 equations used to calculate the energy stored in a spring

Answer 30

E = 1/2 F Δx E = 1/2 k Δx^2 x = extension

Question 31

What does the gradient and area represent on a force-extension graph

Answer 31

- the gradient of the linear region represents the elastic constant (k) - the area is equal to the elastic potential energy stored in the spring

Question 32

Equation to find out the volume an object is submerged

Answer 32

Volume submerged = upthrust / (density x g)

Question 33

What does the area under the line of a of a force/extension graph show and which (force or extension) is on the x axis and which is on the y axis

Answer 33

Y axis = force X axis = Extension The area under the line shows the work done to stretch

Question 34

what does the gradient of a force extension graph represent and define it

Answer 34

The spring constant - a measure of the stiffness of the spring

Question 35

Define upthrust

Answer 35

the upward force that a liquid or gas exerts on a body floating in it.

Question 36

Derive the equation of a falling object ( Weight = upthrust + drag) to get it equaling terminal velocity

Answer 36

V = 2r^2 g (density of object - density of fluid) / 9η

Question 37

During laminar flow, in what way do the fluid layers move

Answer 37

Parallel to each other at different speeds

Question 38

Required conditions for stokes law to apply

Answer 38

Small Spherical Slower speed ( so it doesn’t go into turbulent flow) Laminar flowing liquid

Question 39

Why does the spherical object for stokes law have to be small

Answer 39

If it’s big, the friction between the fluid and the wall will be too big, disrupting, the viscosity

Question 40

Why can you not use work done = f x d when trying to work out the work done in a spring

Answer 40

Because the force is not constant

Question 41

Brittle definition

Answer 41

Hard but liable to break easily

Question 42

Ductile definition

Answer 42

Able to be deformed without losing toughness

Question 43

Polymeric definition

Answer 43

A material that is composed of many monomers

Question 44

Describe the shape of a stress strain graph of a brittle object

Answer 44

It will reach its elastic limit quickly and can’t go past it for very long

Question 45

Describe the shape of a stress, strain graph of a ductile object

Answer 45

It will be able to be past its elastic limit for longer

Question 46

What does the area under a stress strain line represent?

Answer 46

Work per unit of volume

Question 47

How do you work out the strength of an object from a stress strain graph?

Answer 47

The highest stress on the line

Question 48

what is the effect of temperature on viscosity and why

Answer 48

Viscosity will decrease with increased temperature because as particles move more quickly, they interact for shorter time (shorter interactions) reducing internal friction or stress and therefore decreasing viscosity.

Question 49

Where on a graph would you put the limit of proportionality

Answer 49

When it just starts to curve

Question 50

Where on a graph would you put the elastic limit

Answer 50

Just beyond the limit of proportionality

Question 51

Where on a graph would you put the yield point

Answer 51

After this point, it gets much flatter

Question 52

Compare a ductile material to a brittle material

Answer 52

The brittle material has only a linear-elastic region before rupture failure while the ductile materials has a linear-elastic region followed by a region in which plasticity engages.

Question 53

What is breaking stress

Answer 53

The maximum stress a material can stand before it breaks is called the breaking stress or ultimate tensile stress

Question 54

If the student had used the larger sphere, the equation for viscosity would not have produced the correct answer. Explain why.

Answer 54

• With the large sphere the speed will be greater so Stokes' law won't apply • The flow is turbulent or not laminar

Question 55

How does viscosity change when temperature in a gas increases

Answer 55

viscosity of gases increases with an increase in temperature.

Question 56

Yield point definition

Answer 56

Stress at which it stops behaving elastically

Question 57

Why might it be difficult to use stokes law on a bubble

Answer 57

Only for small solid spheres so there will be less drag due to the bubbles having a non-stationary surface