Fundamentals

Question 1

What is a fluid?

Answer 1

A fluid is a substance that deforms continuously under the application of a shear stress.

Question 2

What constitutes as a fluid?

Answer 2

Gases and liquids

Question 3

What are some features of fluids?

Answer 3

• Fluids flow and change shape
• All fluids respond to an applied force or shear stress – they experience a continuing and permanent distortion

Question 4

What are fluids regarded as?

Answer 4

A continuum

Question 5

What can be considered when thinking about the actions of forces on fluids?

Answer 5

• The behaviour of every molecule in a given flow
• The average effects of the molecules in a given volume

Question 6

When does a continuum prevail?

Answer 6

When the number of molecule in a given volume is great that the affects are constant or change smoothly over time

Question 7

When can the continuum approach be justified?

Answer 7

• Number of molecules in a given volume is large
• The scale of interest is not too small

Question 8

What is the definition of density?

Answer 8

mass per unit volume

Question 9

How can specific gravity be calculated?

Answer 9

S = density(fluid)/density(water)

Question 10

How can specific weight be calculated?

Answer 10

lambda = density*g

Question 11

When is air treated as incompressible?

Answer 11

At velocities«speed of sound

Question 12

Is water compressible or incompressible?

Answer 12

Incompressible

Question 13

Which fluid needs larger pressures to compress them?

Answer 13

Liquids

Question 14

What does each fluid element have?

Answer 14

Has a unique velocity

Question 15

What does fluid velocity depend on?

Answer 15

Time

Question 16

What is stress defined as?

Answer 16

Force per unit area

Question 17

How can stress act at a surface?

Answer 17

• Can be normal to the surface
• Or can be a tangential force

Question 18

What can fluid motion cause?

Answer 18

Fluid motion can cause stresses

Question 19

What can stresses cause?

Answer 19

Stresses can cause fluid motion

Question 20

How do normal stresses behave?

Answer 20

Tend to compress / expand the fluid particle without changing its shape

Question 21

How do shear stresses behave?

Answer 21

• Give rise to forces that shear the particle & deform its shape
• Changes shape without changing volume

Question 22

What type of stresses do stationary fluids feel?

Answer 22

Normal only

Question 23

What type of stresses do moving fluids feel?

Answer 23

They feel both normal and shear

Question 24

How is viscosity defined?

Answer 24

Viscosity is a measure of how much resistance a fluid has to shear

Question 25

How is viscosity quantified?

Answer 25

Quantified by the dynamic viscosity 'mu'

Question 26

When is kinematic viscosity used?

Answer 26

When density variations can be neglected (motion)

Question 27

How is kinematic viscosity related to dynamic viscosity?

Answer 27

v = 'mu'/density

Question 28

How is volume flux determined?

Answer 28

dQ= u*dA