Materials

Question 1

Define fluid

Answer 1

Any substance that can flow. Can be a liquid or gas, solids can sometimes behave as fluids - sand.

Question 2

Define density

Answer 2

mass per unit volume.

Question 3

Define upthrust

Answer 3

An upwards force caused by an object displacing fluid.

If the object is completely submerged, the mass of the fluid displaced = volume of object + density of fluid. m=Vp.

Question 4

State Archimedes Principle

Answer 4

The upthrust on an object is equal to the weight of fluid displaced.

Question 5

What is a Hydrometer?

Answer 5

An instrument used to determine density of a fluid.

Question 6

Define Laminar Flow

Answer 6

Fluid moves in parallel layers. The velocity is constant over time.

Question 7

What is the effect of fluid flowing through a pipe?

Answer 7

Friction between the outermost layer and the pipe means this layer moves slower.

Question 8

Define Turbulent Flow

Answer 8

Layers mix. The fluid becomes chaotic and swirling eddies form. Velocity in a particular place changes over time.

Question 9

Define Viscosity.

Answer 9

How resistant a fluid is to flowing.

Question 10

How is flow of fluid and viscosity related?

Answer 10

The rate of flow of a fluid is inversely proportional to the viscosity of the fluid.

Question 11

Stokes Law

Answer 11

F = 6πηrv

Only applies to small spheres at low speeds. Drag force is directly proportional to radius and velocity.

Question 12

pressure=

Answer 12

=Force/Area

=density x g x height

Question 13

Terminal Velocity

Answer 13

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

Question 14

Define Hookes Law

Answer 14

Force needed to extend a spring is proportional to the extension of the spring.

Question 15

A material obeys Hooke’s Law

Answer 15

if it has not passed the limit of proportionality

Question 16

State Hooke’s Law

Answer 16

Force Applied = spring constant x extension.

ΔF = kΔ x

Question 17

Define elastic strain energy.

Answer 17

Work done in deforming a material sample before it reaches elastic limit.
ΔEel = 1/2 FΔ x

Question 18

Compressive force

Answer 18

Squashes the material causing a negative extension.

Question 19

Tension

Answer 19

A force acting within a material in a direction that would extend.

Question 20

Define Stress

Answer 20

Stress σ = F/A

Question 21

Define Strain

Answer 21

Strain ε = Δ x/x

=extension / original length

Question 22

Youngs Modulus, E

Answer 22

E = σ/ε =stress/strain =Fx/AΔ x

E is the stiffness constant of a material,

Question 23

Limit of proportionality

Answer 23

Beyond this point stress is not proportional to strain.

Question 24

Elastic Limit

Answer 24

The material is permanently deformed beyond this point. Sample will not return to original size when stress is released.

Question 25

Yield Point

Answer 25

Sudden increase in extension as atomic structure reorganised

Question 26

Ultimate Tensile Stress

Answer 26

The highest stress value

Question 27

Fracture stress

Answer 27

The value stress will be when the sample breaks.

Question 28

Tough

Answer 28

can withstand dynamic loads / shocks / impacts / absorbs

a lot of energy before breaking

Question 29

Ductile

Answer 29

can be pulled into a long thin shape

Question 30

Brittle

Answer 30

breaks with plastic deformation/ shatters

Question 31

What is meant by a strong

material?

Answer 31

Large force / stress required to break it

Question 32

Upthrust =

Answer 32

pvg = density x volume x gravity

Question 33

Explain the difference between elastic and plastic behaviour in a metal.

Answer 33

Plastic = permanent AND elastic = reversible
Elastic: bonds stretch but not broken / atoms move apart but then return
Plastic: bonds broken (when stressed) / atoms do not return to original position (after stress)

Question 34

Explain the effect turbulence would have on the rate of flow

Answer 34

Reduces the speed / rate of flow

Because turbulence would disperse energy through the mixing/components of fluid follow longer path

Question 35

Suggest how the elastic properties of the waistband help in keeping the trousers in
place.

Answer 35

Elastic tries to return to a smaller/original length. So will be in tension OR applies force /pull