Chapter 4 - Fluids

Question 1

Specific Gravity:

Answer 1

pure water at 1 atm and 4C

the density of a fluid is often compared to this variable

can be used as a tool for determining if an object will sink or float in water

Question 2

Pascal in SI units:

Answer 2

1 Pa = 1 N/m2

Question 3

Absolute (hydrostatic) pressure:

Answer 3

total pressure exertedon an object that is submerged in a fluid

Question 4

Fluids:

Answer 4

characterized by their ability to flow and conform to the shapes of their containers

both liquids and gases

Question 5

Pascal’s Principle:

1. definition
2. main point to remember

Answer 5

1. for fluids that are incompressible (fluids with volumes that cannot be reduced by any significant degree through application of pressure) a change in pressure will be transmitted undiminished to every portion of the fluid and to the walls of the containing vessel
2. the larger the area, the larger the force

Question 6

Archimedes’ principle:

1. definition
2. what to always remember

Answer 6

deals with buoyancy of objects

1. a body wholly or partially immersed in a fluid will be buoyed upwards by a force equal to the weight of the fluid that it displaces

2. use density of the fluid in the equation

Question 7

Floating vs. Sinking:

Answer 7

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 8

Cohesion vs. Adhesion:

Answer 8

Cohesion: attractive force that a molecule of liquid feels toward other molecules of the same liquid

Adhesion: attractive force that a molecule of liquid feels toward other molecules of a different substance

Question 9

Types of meniscus:

Answer 9

concave: more common; when adhesive forces are stronger than cohesive forces
convex: when the cohesive forces are greater than the adhesive forces

Question 10

Viscosity:

1. what it is
2. units

Answer 10

1. resistance of a fluid to flow
2. Pa * s = (N * s)/m2

Question 11

Laminar Flow:

Answer 11

smooth and orderly, modeled as layers of fluid that flow parallel to each other

layers will not necessarily have same speed; layer closest to wall of pipe flows slower than more interior layers of fluid

Question 12

Relationship between radius and pressure gradient:

Answer 12

the relationship is inverse exponential to the fourth power

even a slight change in the radius of the tube has a significant effect on the pressure gradient, assuming a constant flow rate

*Poiseuille’s Law*

Question 13

What is Pouseille’s Law used for:

Answer 13

calculates the rate of flow

laminar flow through a pipe or confined space

Question 14

Turbulent flow:

1. definition
2. what it causes downstream

Answer 14

1. rough and disorderly
2. causes the formation of eddies: swirls of fluid of varying sizes occuring typically on the downstream side of an obstacle

Question 15

Critical Speed:

1. definition
2. when critical speed is exceeded

Answer 15

1. speed, which when overcome, results in turbulent flow

only applicable to unobstructed fluid flow

2. when the critical speed for a fluid is exceeded, the fluid demonstrates complex flow patterns, and laminar flow occurs only in the thin layer of fluid adjacent ot the wall (boundary layer)

Question 16

Streamlines:

Answer 16

indicate the pathways followed by tiny fluid elements (fluid particles) as they move

Question 17

Flow rate:

1. what it is
2. when it is constant

Answer 17

1. volume/time
2. is constant for a closed system and is independent of changes in the cross-sectional area

Question 18

Linear speed;

1. what it is
2. how it changes

Answer 18

1. measure of the linear displacement of fluid particles in a given amount of time
2. changes relative to cross-sectional area

will increase with decreasing cross-sectional area

Question 19

Bernoulli’s equation:

Answer 19

Question 20

As blood flows away from the heart, each vessel has a progessively higher resistance, but the total resistance of the system decreases, why?

Answer 20

the total resistance of the system decreases because the increased number of vessels are in parallel with each other

like parallel resistors in circuits, the equivalent resistance is therefore lower for the capallaires in parallel than in the aorta

Question 21

Continuity Equation:

1. the equation
2. what it means

Answer 21

Q = v1A1 = v2A2

statement of conservation of mass as applied to fluid dynamics

Question 22

Dynamic Pressure:

Answer 22

pressure associated with the movement of a fluid

(1/2)*density*velocity^2

the second part of bernoulli equation

Question 23

Static Pressure:

Answer 23

pressure fluid exerts when it’s not moving

P + pgh (density*acceleration of gravity*height from some datum)

Question 24

Venturi Effect:

Answer 24

As the cross-sectional area decreases from point 1 to point 2, the linear speed must increase according to the continuity equation

as they dynamic pressure increases, the absolute pressure must decrease at point 2

with a lower absolute pressure, the column of fluid stickin up from the Venturi tube will be lower at point 2

As the tube narrows, the linear speed increases at point 2. The pressure exerted on the walls decreases, causing the column to have a lower height at point 2

Question 25

Pitot Tubes:

Answer 25

specialized measurement devices that determine the speed of fluid by determining the difference between the static and dynamic pressure of the fluid at given points along a tube