Chapter 7 - Fluids and Solids

Question 1

According to Archimedes’ principle, the bouyant force acting upon an object is equal to what?

Answer 1

the weight of the fluid displaced

Question 2

What is the elastic limit of a solid?

Answer 2

It is the greatest stress a solid can take and still return back to its original state.

Question 3

What is friction in a fluid called?

Answer 3

viscosity (η)

Question 4

For a floating object, relative densities = what?

Answer 4

% submerged

Question 5

What are the units of viscosity?

Answer 5

N x s/m²

Question 6

What is meant by an elastic solid?

Answer 6

With an applied force, a solid can be bent, compressed, or stretched, but can return to its original state when the force is removed.

Question 7

How does surface tension affects surface area?

Answer 7

As surface tension increases, its surface decreases in area.

Question 8

Equation: Archimedes’ principle of bouyancy

Answer 8

B = ρ_fluid x V_{fluid displaced} x g

Question 9

Equation: viscous retarding force

Answer 9

F = 4πηLv

Question 10

Which materials are most prone to lateral shear?

Answer 10

crystalline solids

Question 11

Define a solid

Answer 11

a material that can hold a definite shape

Question 12

What is the difference between stress and strain?

Answer 12

Stress causes a strain (deformation).

Question 13

What is the characteristic of brittle materials in terms of strain and stress?

Answer 13

Their ultimate tension strengths are close to their fracture stress. They tend to fracture, without deforming much.

Question 14

Equation: Reynolds number (N_R)

Answer 14

N_R = 2ρvR/η

R = radius of vessel

Question 15

Define a fluid

Answer 15

any matter that flows (liquids and gases)

Question 16

What a material’s ultimate tension strength?

Answer 16

the point at which a material is under maximum stress

Question 17

What is meant by turbulent flow?

Answer 17

If the flow of a fluid is sufficiently high, then a chaotic and irregular pattern develops in the fluid.

Question 18

What are the units of density?

Answer 18

kg/m³

Question 19

If the radius of a pipe is doubled, how does this affect the flow rate?

Answer 19

Flow rate increases by a factor of 16.

Question 20

Describe pascal’s principle.

Answer 20

A pressure applied to an enclosed fluid is transmitted equally throughout the fluid and to the walls of the fluid’s container.

Question 21

Equation: density

Answer 21

ρ = mass/volume

Question 22

Equation: velocity of fluid at the center of a pipe

Answer 22

v = [(P₁ - P₂)/4ηL] r²

Question 23

What is the characteristic of ductile materials in terms of strain and stress?

Answer 23

They have fracture strains far above their ultimate tension strength. They deform a lot before they fracture.

Question 24

Equation: strain (ε)

Answer 24

Strain = ε = change in dimensional length/original dimensional length = ΔL/L

Question 25

What are the units of pressure?

Answer 25

pascal (Pa) = N/m²

Question 26

Equation: specific gravity/relative density

Answer 26

specific gravity = ρ_relative = ρ_material/ρ_{H2O at 4ºC}

Question 27

Equation: Pascal’s principle of pressure

Answer 27

P₁ - P₂ = ρ(y₂ - y₁)g

Question 28

When does a solid material become fractured?

Answer 28

when strain is increased beyond a solid’s maximum tension strength

Question 29

Equation: Bernoulli’s equation relating fluid pressures (2 versions)

Answer 29

P₁ +1/2ρv₁² + pgy₁ = P₂ + 1/2ρv₂² + pgy₂

k = P_{against inner walls} + 1/2ρv² + ρgh

Question 30

If an object has a greater bulk modulus (B), what does this say about its ability to deform?

Answer 30

It does not deform easily. Its volume remains mostly unchanged (cyrstalline solids).

Question 31

As a simple fluid flows through a pipe, describe its flow rates near the edges versus the center.

Answer 31

Fluid in the center of the pipe flows the fastest, while fluid at the edges of the pipe flows the slowest (speed is almost 0).

Question 32

Equation: Poiseuille’s principle of flow rate (Q)

Answer 32

Q = (πr⁴/8ηL) (P₁ - P₂)

Question 33

What are the units of stress?

Answer 33

N/m²

Question 34

Equation: stress (σ)

Answer 34

Stress = σ = Force/Area

Question 35

How do pressures and velocities of air differ above and below a plane’s wing?

Answer 35

The top of the wing is curved, so it is longer than the bottom. Air must move faster across the top, resulting in a decreased pressure compared to the bottom of the wing. This allows lift.

Question 36

If a cross-sectional area is smaller at the beginning of a pipe than the cross-sectional area at the end, how do the speeds of the fluid compare?

Answer 36

At the beginning, the speed with be faster than at the end.

Question 37

Equation: continuity of flow rate

Answer 37

Q = A₁V₁ = A₂V₂

Question 38

For sunken objects, relative densities = what?

Answer 38

W/F_bouyant ratio

Question 39

Equation: flow rate (Q) in terms of volume

Answer 39

Q = V/t

Question 40

Equation: pressure

Answer 40

P = F⊥/A

Question 41

Equation: Bulk moldulus (B)

Answer 41

B = -ΔP/(ΔV/V₀)

Question 42

When is a solid material plastically deformed?

Answer 42

when it has passed its elastic limit

Question 43

Stress-strain graph

Answer 43

Question 44

What numbers correspond to laminar or turbulent flow?

Answer 44

Laminar: N_R < 2000

Turbulent: N_R > 3000

Unstable: 2000 > N_R > 3000

Question 45

What is meant by laminar/streamline flow?

Answer 45

Adjacent layers of a fluid have the ability to slide past one another in a smooth and uniform fashion.

Question 46

If a cross-sectional area is smaller at the beginning of a pipe than the cross-sectional area at the end, how does the flow rate of the fluid compare?

Answer 46

It is the same along the entire pipe.

Question 47

Equation: Young’s modulus Y of a solid’s elasticity

Answer 47

E = Y = Stress/Strain = σ/ε = (F/A)/(ΔL/L)

Question 48

What is meant by bulk deformation and what is the result?

Answer 48

As pressure increases on all sides of an object, the object decreases in volume.

Question 49

How does temperature change affect the viscosity of a liquid and gas?

Answer 49

As temperature increases, fluid viscosity decreases, while gaseous viscosity increases.

Question 50

Equation: cross-sectional area of a pipe

Answer 50

A = πr²

Question 51

When fluid velocity increases in a pipe, how is pressure affected?

Answer 51

Pressure will decrease.