Chapter 5: Fluids and Solids

Question 1

Fluid

Answer 1

Ability to flow and conform to the shape of its container; liquids and gases

Question 2

Solid

Answer 2

Does not flow; rigidity helps it retain a shape independent of that of any container

Question 3

Common characteristics of fluids and solids

Answer 3

Both can exert forces perpendicular to their surface, only solids can withstand shear (tangential forces)

Question 4

Density

Answer 4

• scalar quantity
• (rho) = m/V
• units = kg/m^3

Question 5

Calculating weight using density

Answer 5

W = mg
m = (rho)V
W = (rho)Vg

Question 6

Specific gravity

Answer 6

Ratio of the density of a substance to the density of water; density of H2O = 1000 kg/m^3 = 1g/cm^3

• if specific gravity > 1, substance more dense than water
• if specific gravity < 1, substance less dense than water

Question 7

Pressure

Answer 7

P = F(N)/A

• unit = Pascal (1 Pa = 1 N/m^2)
• other units: 1.013 x 10^5 Pa = 1 atm = 760 torr = 760 mm Hg
• scalar quantity

Question 8

Absolute pressure

Answer 8

• the total pressure that is exerted on an object that is submerged in a fluid
  P = P(0) + (rho)gh

Question 9

Gauge pressure

Answer 9

• the difference between absolute and atmospheric pressure; the pressure in a closed space above atmospheric pressure
  P(g) = P - P(atm) = [P(0) + (rho)gh] - P(atm)

Question 10

Hydrostatics

Answer 10

the study of fluids at rest and the forces and pressures associated with standing fluids

Question 11

Pascal’s principle

Answer 11

For fluids that are incompressible, when a change of pressure is applied to an enclosed fluid, that pressure change will be transmitted undiminished to every portion of the fluid and to the walls of the containing vessel
P = F(1)/A(1) = F(2)/A(2)
F(2) = F(1) [A(2)/A(1)]

         V = A(1)d(1) = A(2)d(2)
         d(2) = d(1) [A(1)/A(2)]

         W = P∆V = F(1)/A(1) [A(1)d(1) = F(2)/A(2) [A(2)d(2)]
         W = F(1)d(1) = F(2)d(2)

Question 12

Archimedes principle

Answer 12

A body wholly or partially immersed in a fluid will be buoyed up by a force equal to the weight of the fluid that displaces it
- force directed upward = buoyant force
F(buoy) = V(fluid displaced)[rho(fluid)]g = V(object submerged)[rho(fluid)]g
- an object will float, no matter what it is made of and no matter how much mass it has, if its average density is less than or equal to the density of the fluid into which it is placed; an object will sink if its average density is greater than the density of fluid displaced

Question 13

Molecular forces in liquids

Answer 13

Surface tension = causes liquid surface to form a thin, but strong, layer, results from cohesion
Cohesion = attractive force that a molecule of liquid feels toward other molecules of the liquid
Adhesion = attractive force that a molecule of liquid feels toward the molecules of some other substance

Question 14

Hydrodynamics

Answer 14

the study of fluids in motion

Question 15

Viscosity

Answer 15

The resistance of a fluid to flow; fluid friction

- ideal fluids have no viscosity

Question 16

Laminar and turbulent flow

Answer 16

• Laminar flow = smooth and orderly, imagine concentric layers of fluid that flow parallel to each other
• Turbulent flow = rough and disorderly; causes the formation of eddies; can arise when the velocity of the fluid exceeds a certain critical velocity [v(c)]
  v(c) = N(R) (eta) / [(rho)D]

Question 17

Streamlines

Answer 17

• representations of the molecular movement

- indicate the pathway followed by tiny fluid elements as they move

Question 18

Volumetric flow rate for changing cross-sectional area

Answer 18

• volumetric flow rate (ie. units of volume per units of time) is constant for a closed system and is independent of changes in cross-sectional area

Question 19

Linear velocity

Answer 19

• units = m/s

- measure of the linear displacement of a fluid particle in a given amount of time

Question 20

Continuity equation

Answer 20

v(1)A(1) = v(2)A(2) = constant

• fluids will flow more quickly through narrow passages and more slowly through wider ones

Question 21

Bernouilli’s Equation

Answer 21

• Fluids have higher velocities through narrower tubes

P(1) + [(rho)v(1)^2/2] + (rho)gy(1) = P(2) + [(rho)v(2)^2/2] + (rho)gy(2) = constant

• dynamic pressure = pressure associated with the movement of the fluid = (rho)v(1)^2/2 and (rho)v(2)^2/2
• static pressure = P + (rho)gy(1) and P + (rho)gy(2)
• for an incompressible fluid not experiencing friction forces, the sum of the static pressure and dynamic pressure will be constant within a closed container

Question 22

Young’s modulus

Answer 22

• When a stretching (tensile) or pushing (compression) force is exerted against an object, the object will experience a change in length
• applied pressure = stress
• change in length per unit length = strain

   Y = (F/A) ÷ (∆L/L)

Question 23

Shear modulus

Answer 23

• If a force is applied parallel to an object’s surface, the object will experience a shape change known as a shear; causes a lateral shift in the direction of the force

  S = (F/A) ÷ (x/h)

Question 24

Bulk modulus

Answer 24

• the degree to which a material will experience a change in its volume in relation to an applied pressure
• Solids and liquids have large bulk moduli, gases have relatively small bulk moduliB = (F/A) ÷ (∆V/V)
• Speed of sound is proportional to the square of the root of the bulk modulus, sound will travel fastest through solids and slowest through gases