Fluid Properties

Question 1

What is Hydraulics?

Answer 1

Branch of applied science and engineering which deals with mechanical properties and motion of fluids.

Question 2

What is fluid dynamics?

Answer 2

Application of fundamental principles of general mechanics to fluids.

Question 3

What are three mechanical properties of fluids?

Answer 3

Density, viscosity and surface tension.

Question 4

What are the two types of motion for a fluid?

Answer 4

Closed conduits (pipes) which have no free surface and channels with a free surface.

Question 5

What is the definition of a fluid?

Answer 5

A substance that continuously deforms or flows under an applied shear stress.

Question 6

What can a fluid at rest not resist?

Answer 6

Shear stress.

Question 7

What is a liquid?

Answer 7

A fluid which when placed in an open container, takes the shape of the container and has a free surface.

Question 8

What is a gas?

Answer 8

A fluid which when placed in an open container expands to fill the container.

Question 9

Which is denser; liquid or gas?

Answer 9

Liquid, it contains more molecules per unit volume.

Question 10

What is density?

Answer 10

Mass of a given amount of a substance (m) to the volume it occupies.

Question 11

What is the density of water taken to be?

Answer 11

1000 kg/m^3.

Question 12

What does the exact density of water vary with?

Answer 12

Temperature, it’s 1000 kg/m^3 at 4 degrees Celsius.

Question 13

What is the density of typical seawater with 35% salinity?

Answer 13

1025 kg/m^3.

Question 14

What is relative density/specific gravity?

Answer 14

The ratio of the density of a substance to that of pure water.

Question 15

What is the dimensions of relative density?

Answer 15

Dimensionless.

Question 16

What is the unit weight of a substance?

Answer 16

The ratio of the weight of a given amount of a substance (W) to the volume it occupies.

Question 17

What are the SI units of unit weight?

Answer 17

N/m^3.

Question 18

What causes pressure in a fluid?

Answer 18

Continual movement of molecules means that any part of a fluid experiences forces exerted by adjoining fluid or solid boundaries as a result of the action of innumerable molecular collisions.

Question 19

What is pressure (p) equal to?

Answer 19

The normal force applied to a surface element of a fluid divided by its area.

Question 20

What is the SI units of pressure?

Answer 20

Pascals (Pa) = N/m^2. Pressure can also be given in atmospheres, where 1 atm = 1.01325x10^5 Pa.

Question 21

How do instruments determine pressure?

Answer 21

Pressure cannot be measured directly. It is determined by the difference in pressure between two points.

Question 22

What are the two types of reference pressure?

Answer 22

Absolute and gauge pressure.

Question 23

What is absolute pressure?

Answer 23

Where pressure is given relative to pressure in a perfect vacuum.

Question 24

What is gauge (relative) pressure?

Answer 24

Where pressure is given relative to the local atmospheric pressure.

Question 25

Which form of pressure do meteorologists use?

Answer 25

Absolute as it ensures all values are positive.

Question 26

Which form of pressure do civil engineers normally use?

Answer 26

Gauge, as it is what is typically acting on structures.

Question 27

What is absolute pressure at sea level?

Answer 27

101.3kPa.

Question 28

What is compressibility of a fluid expressed by?

Answer 28

Bulk modulus of elasticity, E.

Question 29

What is bulk modulus of elasticity (E)?

Answer 29

The ratio of the increase in pressure to the resulting volumetric strain.

Question 30

What does an increase in pressure result in?

Answer 30

Higher density and reduced volume.

Question 31

What does a decrease in pressure result in?

Answer 31

Lower density and increased volume.

Question 32

Is bulk modulus of elasticity greater for liquids or gases?

Answer 32

Liquids.

Question 33

What is the bulk modulus of elasticity for water at 20 degrees Celsius?

Answer 33

2.2x10^9 Pa = 2.2 GPa

Question 34

What do we assume for the compressibiltiy of water?

Answer 34

That it's incompressible and density is constant.

Question 35

What is the viscosity of a fluid?

Answer 35

A measure of its resistance to gradual deformation by shear or tensile stress.

Question 36

Will a more viscous fluid deform faster or slower than a less viscous fluid?

Answer 36

Slower.

Question 37

What is Newton's law of viscosity?

Answer 37

Shear stress = dynamic viscosity (mew) x velocity gradient (du/dy).

Question 38

What are the SI units of dynamic viscosity?

Answer 38

Pa.s. Pascal seconds.

Question 39

What are Newtonian fluids?

Answer 39

Fluids that conform to Newton's law of viscosity.

Question 40

What is viscosity dependent on for non-Newtonian fluids?

Answer 40

Rate of shear or shear history.

Question 41

What is a negative implication of non-Newtonian fluids?

Answer 41

If a house is built on clay and and earthquake puts stress on the ground, the clay can liquefy.

Question 42

What is a positive implication of non-Newtonian fluids?

Answer 42

Body armour has been developed that behaves like a liquid for easy movement, but becomes solid on impact.

Question 43

What is viscosity independent to?

Answer 43

Pressure changes.

Question 44

What is kinematic viscosity (new)?

Answer 44

Ratio of dynamic viscosity to density.

Question 45

What are the SI units of kinematic viscosity?

Answer 45

m^2/s.

Question 46

What causes surface tension?

Answer 46

Molecules on the surface of a fluid have no molecules above to have a cohesive force to thus cohere more strongly to other surface molecules, creating the effect of a membrane covering the surface.

Question 47

What is the effect of surface tension?

Answer 47

Things with a higher density than water, e.g. spider, can sit on the surface. They're not floating as should sink.

Question 48

How does surface tension cause water to form into droplets?

Answer 48

Intermolecular forces mean that a small un-enclosed volume of liquid tends to be pulled into a spherical shape by cohesive forces on surface layer.

Question 49

What is surface tension usually measured in?

Answer 49

dynes/cm. 1 dyne/cm = 0.001 N/m

Question 50

What is adhesion?

Answer 50

The attractive force which occurs between the molecules of a liquid and a solid.

Question 51

What does the angle of contact of a liquid-gas interface with a solid surface depend on?

Answer 51

Relative magnitudes of adhesion of liquid molecules to solid molecules and the cohesion of the liquid molecules to each other.

Question 52

When is a solid surface said to be completely wetted?

Answer 52

When adhesion exceed cohesion, e.g. water and a clean glass surface.

Question 53

When is wetting negligible?

Answer 53

When cohesion greatly exceeds adhesion. E.g. mercury and glass.

Question 54

If the solid surface is wetted does the free liquid surface curve up or down?

Answer 54

Up, it curves down with negligible wetting.

Question 55

What causes capillary rise?

Answer 55

Surface tension and adhesion.

Question 56

What is capillary rise?

Answer 56

If a tube is sufficiently narrow and liquid adhesion is sufficiently strong, a meniscus will form and surface tension can support the weight of liquid in the tube and draw the liquid up the tube.

Question 57

When can capillary rise be negative?

Answer 57

If theta is greater than 90 degrees e.g. mercury in glass.