Materials

Question 1

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

Answer 1

Elastic potential energy

Question 2

What is the yield point?

Answer 2

The point at which the object will experience a large extension without an increase in stress

Question 3

What does the area underneath a force-extension graph represent?

Answer 3

The area us equal to the elastic potential energy stored in the spring

Question 4

What unit is the Young’s Modulus measured in?

Answer 4

Nm⁻² or Pa

Question 5

State the equation for Young’s Modulus.

Answer 5

Stress / Strain

Question 6

What is the unit of strain?

Answer 6

There is no unit, it is a ratio of the extension and original length

Question 7

State the equation of strain?

Answer 7

Extension / Original length

Question 8

What is elastic deformation?

Answer 8

Deformation where a material can return to its original shape and size, after an applied stress is released. Any work done is stored as elastic potential energy

Question 9

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

Answer 9

• Upthrust = weight of displaced fluid
  So therefore maximum upthrust is ρ(f)Vg
• Weight = ρ(o)Vg
  Therfore if ρ(o) is greater than ρ(f) then the weight will always be greater than the upthrust and the object will sink

Question 10

What determines whether an objecy floats or sinks?

Answer 10

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

Question 11

What is the density of a material?

Answer 11

Its mass per unit volume

Question 12

What is the unit of stress?

Answer 12

Nm⁻² or Pa

Question 13

State the equation of Hooke’s Law.

Answer 13

F = kx

Question 14

State the Stoke’s Law equation

Answer 14

F=6πrηv
F = viscous drag force
η = viscosity of the fluid
r = radius of sphere
v = velocity of sphere

Question 15

What is required for Stoke’s Law to apply?

Answer 15

Laminar flow

Question 16

What shaped objects does Stoke’s law apply to?

Answer 16

Small, spherical objects

Question 17

What is the unit for density?

Answer 17

kgm⁻³

Question 18

State the equation for stress?

Answer 18

Force / Cross-sectional area

Question 19

What is stress?

Answer 19

The force per unit area experienced by an object

Question 20

Explain Hooke’s Law.

Answer 20

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

Question 21

What is the Young’s Modulus?

Answer 21

A measure of how much force is required for a given extension, regardless of the object’s dimensions

Question 22

What does Stoke’s Law allow you to calculate? What conditions are necessary?

Answer 22

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

Question 23

What does the gradient on a force-extension graph represent?

Answer 23

The elastic constant (k)

Question 24

What is breaking stress?

Answer 24

The maximum stress that an object can withstand before fracturing

Question 25

What is the elastic limit?

Answer 25

The point beyond which the object will no longer deform elastically and will instead deform plastically. Beyond this point the object will be permanently deformed

Question 26

What is plastic deformation?

Answer 26

An object has undergone plastic deformation if it no longer returns to the original shape after the deforming forces are removed. It will have permanent deformation. Some work done will be dissipated as heat

Question 27

What is the limit of proportionality?

Answer 27

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

Question 28

State the two equations used to calculate elastic potential energy.

Answer 28

E = 1/2 fx E = 1/2 kx^2

Question 29

What is Archimede's principle?

Answer 29

When an object is submerged in a fluid the weight of the fluid is displaced. This produces the force of upthrust

Question 30

What happens to the viscosity of liquids and gases when temperatures increases?

Answer 30

For gases, viscosity increases as temp increases For liquids, viscosity decreases as temp increases

Question 31

What is laminar flow?

Answer 31

Its where a fluid moved with uniform lines in which the velocity is constant over time. In laminar flow, the lines are streamlines

Question 32

What is the ultimate tensile stress?

Answer 32

The ultimate tensile stress is the maximum stress that the material can withstand before the breaking stress

Question 33

What is viscous drag?

Answer 33

The frictional force between a solid and a fluid.

Question 34

What is the coefficient for viscosity?

Answer 34

A numerical value given to a fluid to indicate how much it resists flow

Question 35

What is terminal velocity?

Answer 35

The velocity of a falling object when its weight is balanced by the sum of the drag and upthrust acting on it

Question 36

What is viscosity?

Answer 36

A meaure of how resistant a fluid is to flowing

Question 37

What is turbulent flow?

Answer 37

Where fluid velocity in a particular place changes over time, often in an unpredictable manner. It is chaotic and 'eddies' form which are swirls, it increases drag

Question 38

What is a hydrometer?

Answer 38

A hydrometer determines the density of a fluid. It has a constant weight so will sink lower in fluids of less density. there are scale markings on the side of the hydrometer to indicate the density of the liquid

Question 39

What are streamlines?

Answer 39

Lines of laminar flow in which the velocity is constant over time

Question 40

WHy do car manufacturers try to avoid turbulent flow?

Answer 40

Turbulent flow increases the drag on a vehicle and so increases fuel consumption

Question 41

What happens to the spring constant for two springs in series?

Answer 41

k is halved

Question 42

What happens to the spring constant for 2 springs in parallel

Answer 42

k is doubled

Question 43

What is the equation of youngs modulus in terms of force,area, extension and original length?

Answer 43

E = FL / AΔL

Question 44

What does the difference in area between loading and unloading of a force-extension graph when the limit of proportionality has been passed but the elastic limit has not?

Answer 44

The energy lost as heat during loading and unloading

Question 45

Explain the features of a Stress-strain graph that a ductile material will have?

Answer 45

It will have a large plastic region as it can be drawn into long wires, eg copper

Question 46

Explain the features of a Stress-strain graph that a brittle material will have?

Answer 46

It will have a high Youngs Modulus (gradient) and no plastic region

Question 47

How will the stress-strain graoh of a material with a high Young's Modulus compare with that of a material with a lower one?

Answer 47

High YM will lead to a high gradient and vice versa