Materials

Question 1

Density

Answer 1

“Mass per unit of volume” in kgm-3

Density = Mass/Volume

Question 2

Pressure

Answer 2

“Force per unit of area” Pa = kgm-1s-2

Pressure = force/area

Question 3

Laminar flow

Answer 3

Occurs when there is no crossing of layers and no sudden changes in velocity. Velocity at a point is constant

Question 4

Turbulent flow

Answer 4

Occurs when there is a crossing of layers, sudden changes in velocity and eddies form. Velocity at a point is not constant

Question 5

Stokes’ Law

Answer 5

F = 6(Pi)(Eta)rv

Question 6

Viscous Drag

Answer 6

The frictional force due to a fluids viscosity
Rate of flow of a fluid = Volume/time m3s-1
Flow rate = Area x Length / time
Flow rate = Area x Speed

Question 7

Viscous Drag

Answer 7

Always opposes the dirictin of motion and increases as the object speeds up
Weight = Upthust + Viscous Drag for sinking
Upthust = Weight + Viscous Drag for rising

Question 8

Upthrust

Answer 8

The upward force exerted on an objectimmersed in fluid
U = VoPfg
Upthrust = Volume of the object x Density of the fluid x gravity

Question 9

Archemedes’ Principle

Answer 9

“The upthrust acting on an object immersed in a fluid is equal to the weight of the fluid displaced”

Question 10

Terminal velocity

Answer 10

The maximum falling velocity when an object’s two upwards forces match the downwards weight

Question 11

Hooke’s Law

Answer 11

“The force, F, applied to a material is directly proportional to the chane in length of the material, Δx”
F = KΔx (N)
Object that follow’s Hooke’s Law: Metal Spring

Question 12

Force-Extension Graph

Answer 12

y axis: Force / N
x axis: Extension / m
Straight line through the origin
Gradient = Spring Constant (K) / Nm-1

Question 13

Elastic Energy

Answer 13

Elastic energy = 0.5FΔx
Elastic energy = 0.5KΔx^2
Elasti energy = 0.5(Spring constant)(Extension)^2

Question 14

Limit of proportionality

Answer 14

This is the point beyond which force and extesion are no longer proportional
(The end of the straight line that obeys Hooke’s Law on a graph)

Question 15

Elastic limit

Answer 15

The point beyond which permanent deformation occurs and so the material does not return to it’s origional length when the force is removed

Question 16

Yeild point

Answer 16

A larger increase in extension occurs here, for a small increase in force

Question 17

Tensile Stress (σ)

Answer 17

The ratio of tensile force to cross-sectional area. Allows us to compare materials ability to hold tensile forces. Nm-2 = Pa
σ = F/A
Stress = Force/Cross-Sectional Area

Question 18

Tensile force

Answer 18

An applied force that causes tension in the material often causing an extension

Question 19

Tensile Strain (ε)

Answer 19

An extension per unit length. Allows us to compare how different materials deform
ε = Δx/x
Strain = Change in length/Origional length

Question 20

Young Modulus

Answer 20

The mesure of elasticity of a material. (E) It is a ratio of Stress to Strain
E = σ/ε => Young Modulus = Stress/Strain
E = Fx/AΔx

Question 21

Ultimate Tensile Strength

Answer 21

The maximum stress required to break the material

Question 22

Stiffness

Answer 22

An objects ability to withstand tensile forces

Question 23

Toughness

Answer 23

A materials ability to withstand impact forces and absorb a lot of energy before breaking

Question 24

Brittleness

Answer 24

A material’s tendency to fracture under stress

Question 25

Hardness

Answer 25

A materials ability to resist scratching

Question 26

Stress-Strain graph

Answer 26

Gradient of the linear section - Young’s Modulus
Limit of proportionality - Object follows Hooke’s law up to this point, end of linear section
Elastic limit - Up to this point the wire will return to its origional state, just past the the limit of proportionality
Yeild point - Where we begin to see a large increase in strain for a small amount of stress
Ultimate tensile strength - Peak point of the graph
Area under the graph = Strain energy density

Question 27

Elastic deformation

Answer 27

Deformation that returns to its original stae when released

Question 28

Plastic deformation

Answer 28

Produces a permanent deformation and arises because the material has been loaded beyond its elastic limit.