Chapter 4: Fluids

Question 1

fluids

Answer 1

ability to flow and conform to shapes in their containers

Question 2

solids

Answer 2

do not flow and are rigid

Question 3

density

Answer 3

ρ = m / V

m = mass
V = volume

unit: kg/m^3 or g / ml or kg / cm^3

Question 3

weight if any volume of a given substance with known density can be calculated:

Answer 3

Fg = ρ V g

ρ = density
V = volume
g = gravity

Question 4

specific gravity (SG)

Answer 4

SG = ρ / 1 g /cm^3

Question 5

pressure

Answer 5

P = F / A

P = pressure
F = force
A = area

units: pascal (Pa) = 1 N/s^2

Question 6

pressure units conversions

Answer 6

1.013x10^5 Pa = 760mmHg = 76o Torr = 1atm

Question 6

how can we calculate the difference in prressure?

Answer 6

Fnet = PnetA
Fnet = (Poutside - Pinside) A

Question 7

absolute (hydrostatic) pressure

Answer 7

total pressure that is exerted on an object that is submerged in a fluid

P = Po + ρ g z

P = absolute pressure
Po = ambient pressure (pressure at the surface)
ρ = density
g = gravity
z = depth of the object

Question 8

Gauge pressure

Answer 8

difference between the absolute pressure and the atmospheric pressure

Pgauge = P - Patm = (Po + ρgz) - Patm

note that when Po = Patm, then Pgauge = P - Po = ρgz

Question 9

hydrostatic

Answer 9

Study of fluid at rest and the forces and pressure associated with standing fluids.

Question 10

pascal principle

Answer 10

Changing pressure will be transmitted undiminished to every portion of the fluid into the walls of the container.

Question 11

pascals equations

Answer 11

P = F1/A1 = F2/A2

F2 = F1 (A2/A1)

Question 12

volume of fuid displaced by piastal 1 will be the same volume of liquid displced by piston 2

Answer 12

V = A1d1 = A2d2

d2 =d1 (A1/A2)

Question 13

Archimedes’ priciple deals with buoyancy of objects when placed in a fluid

Answer 13

the mass of the fluid displaced exerts a force equal to its weight agaisnt the submerged object

Question 14

buoyancy

Answer 14

Fbuoy = ρfluid Vfluid displaced g = ρfluid Vsubmerged g

One way to conceptualize the buoyance form is that it is the force of the liquid. Trying to return to the space from which it was displaced. That was trying to push the object up and out of the water.

Question 14

float VS sink

Answer 14

An object will float if its average density is less than the average density of the fluid it is immersed in. It will sink if its average density is greater than that of the fluid.

Question 15

cohesion

Answer 15

It occurs between molecules with the same properties. It is the attractive force that a molecule of liquid fuel stores other molecules of the same liquid. This established the incision in the plane of the surface of the water. When there is an indentation on the surface, then the cohesion could lead to a net upward force.

Question 16

adhesion

Answer 16

Force that a molecule of the liquid fuel stored the molecules of some other substance. When liquids are placed in containers and meniscus or curved surface in which the liquid curls up the side of the container. A small amount will form when the adhesive forces are graded in the cohesive forces.

Question 17

Surface tension.

Answer 17

Causes the liquid to form a thin but strong layer like a “skin” and the liquid surface.

Question 17

Backwards Meniscus.

Answer 17

Occurs when the cohesive forces are greater than the adhesive forces

Question 18

Laminar flow.

Answer 18

It is smooth and orderly. In his, often modelled as layers of fluid that flow parallel to each other.

Question 18

Poiseuille’s law.

Answer 18

Q = πr^4 ΔP / 8 η L

Q = flow rate
r = radius of the tube
ΔP = pressure gradient
η = viscosity
L = lenght of the pipe

Note that the relationship between the radius and pressure gradient is inverse exponential to the 4th power. Even a very slight change in the radius of a tube has significant effect on the pressure gradient.

Question 19

viscosity (η)

Answer 19

Increase viscosity of a fluid increases its viscous drag, which is a nonconservative form that is innocuous to irresistible. Low viscosity means they flow easily.

Question 19

flow rate is constant for a closed system and is independent of changes in cross=sectional area

Answer 19

Q = v1 A1 = v2 A2

Q = flow rate
v1 and v2 = linear speeds
A1 and A2 = areas

This is the continuity equation and it tells us the fluid will flow more quickly through narrow passages and move slowly through wider ones.

Question 20

streamlisnes

Answer 20

Indicates the pathway followed by tiny fluid elements as they move.

Question 20

turbulent flow

Answer 20

rough and disorderly. Eddies which are swirls of fluid in the downstream side of an obstacle.

Question 21

bernoulli’s equation

Answer 21

P1 + 1/2 ρ v1^2 + ρg h1 = P2 + 1/2 ρv2^{2} + ρg h2

ρ = fluid density
g = acceleration due to gravity
P_{1} = pressure at elevation 1
v_{1} = velocity at elevation 1
h_{1} = height of elevation 1
P_{2} = pressure at elevation 2
v_{2} = velocity at elevation 2
h_{2} = height at elevation 2

Question 21

Bernoulli’s equation explained

Answer 21

Expression of conservation of energy for a flowing fluid. This equation states that the sum of the static pressure in the dynamic pressure will be constant between any two points in a closed system.

Question 22

Venturi effect.

Answer 22

For a horizontal flow there is an inverse relationship between pressure and speed, and in a closed system there is a direct relationship between cross-sectional area and pressure exerted on the walls of the tube.

Question 22

Fluid in Physiology.

Answer 22

The circulatory system behaves as a closed system with non constant flow.

Resistance decreases as the total cross-sectional area increases. Arterial circulation is primarily motivated by the heart. Venous Circulation has three times the volume of arterial circulation and is motivated by the skeletal musculature and expansion of the heart. Inspiration and expiration create a pressure gradient not only for the respiratory system, but for the circulatory system as well.