Fluid Mechanics

Question 1

study of fluids at rest in equilibrium situations

Answer 1

Fluid statics

Question 2

study of fluids in motion

Answer 2

Fluid mechanics

Question 3

Application Areas of Fluid Mechanics (7)

Answer 3

• Industrial applications
• Piping and plumbing systems
• Aircraft and spacecraft
• Human body
• Natural flows and weather
• Power plants
• Boats

Question 4

Intermolecular bonds are strongest in _______ and weakest in __________.

Answer 4

solids
gases

Question 5

The molecules in a _____ are arranged in a pattern that is repeated throughout.

Answer 5

Solid

Question 6

In _________ molecules can rotate and translate freely

Answer 6

liquids

Question 7

In the ____ phase, the molecules are far apart from each other, and molecular ordering is nonexistent

Answer 7

gas

Question 8

The arrangement of atoms in different phases:
(a) molecules are at relatively fixed positions in a ________ ,
(b) groups of molecules move about each other in the ________ phase, and
(c) individual molecules move about at random in the ______ phase.

Answer 8

a. solid
b. liquid
c. gas

Question 9

In a liquid, groups of molecules can move relative to
each other, but the volume remains relatively constant
because of the ___________ between the
molecules. As a result, a liquid takes the shape of the
container it is in.

Answer 9

strong cohesive forces

Question 10

A gas expands until it encounters the walls of the
container and fills the entire available space. This is
because the gas molecules are widely spaced, and the
________________ between them are very small. Unlike
liquids, a gas in an open container cannot form a free
surface

Answer 10

cohesive forces

Question 11

A _________ is any substance that can flow

Answer 11

fluid

Question 12

___________ or more precisely, the ______________, of a substance is its mass per unit volume, for a pure substance the density has the same numerical value as is mass concentration. Each materials have different ___________.

Answer 12

Density or Volumetric mass density

Question 13

is the ratio of the density of a substance to the density of a reference substance;

equivalently, it is the ratio of the mass of a substance to the mass of a reference substance for the same given volume

Answer 13

specific gravity

Question 14

ratio of an object’s density to the density of water at 4.0 oC

Answer 14

specific gravity (s.g.) or “relative density” = 1000 kg/m3

Question 15

It is a dimensionless quantity

Answer 15

specific gravity

Question 16

If a substance’s relative density is less than one then it is ___________ than the reference;

if greater than 1 then it is ________than the reference.

If the relative density is exactly 1 then the densities are _______

Answer 16

less dense
denser
equal

Question 17

defined as the normal force F per unit area A over which the force is applied.

Answer 17

pressure

Question 18

Does not require a knowledge of the behavior of individual molecules and provides a direct and easy way to analyze engineering problems

Answer 18

Macroscopic` or classical approach

Question 19

Based on the average behavior of large groups of individual molecules.

Answer 19

Microscopic or statistical approach

Question 20

_________ at a point is defined as the normal force per unit area

Answer 20

Pressure

Question 21

a small surface of area (dA) within a fluid at rest:

The surface does not accelerate, so the surrounding fluid exerts equal _______ forces on both sides of it.

The fluid cannot exert any force parallel to the surface, since that would cause the surface to ______

Answer 21

normal forces
accelerate

Question 22

The pressure at the top is the_____________.
The pressure at the bottom has the same value p.
The pressure is the same at any two points at the same level.
The shape of the container does not matter.

Answer 22

atmospheric pressure

Question 23

• pressure of the earth’s atmosphere
• varies with weather changes and with elevation.

Answer 23

atmospheric pressure

Question 24

At sea level the normal atmospheric pressure is ___ atmosphere (atm) is given by _________ Pa.

Answer 24

1 atm = 1.013x10^5 Pa.

Question 25

Pressure is measured using two references:

Answer 25

• Atmospheric pressure
• Absolute vacuum/zero pressure

Question 26

difference between unknown pressure and atmospheric pressure

Answer 26

Gauge pressure

Question 27

true pressure; includes the atmospheric pressure

Answer 27

Absolute pressure

Question 28

Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.

Answer 28

Pascal’s Law

Question 29

________’ principle:

When a body i s completely or partially immersed in a fluid, the fluid exerts an upward force, called the ________, on the body equal to the weight of the fluid displaced by the body.

Answer 29

Archimedes

buoyant force

Question 30

occurs because the upward pressure on the bottom surface of a submerged object is greater than the downward pressure on top of its surface

Answer 30

Buoyant force

Question 31

is equal to the weight of the displaced water

Answer 31

the buoyant force

Question 32

If the object is totally submerged, the direction of motion of an object submerged in a fluid is determined only by the ________of the object and the fluid.

Answer 32

densities

Question 33

density of object < density of fluid

Answer 33

Fg < B
object accelerates upward

Question 34

density of object > density of fluid

Answer 34

B < Fg
object sinks

Question 35

if the object is _______

• the fraction of the volume of a floating object that is below the fluid surface is equal to the ratio of the density of the object to that of the fluid.
• the upward buoyant force is balanced by the downward gravitational force acting on the object.

Answer 35

floating (partially submerged),

Question 36

The flow becomes _________ if the fluid’s speed exceeds a certain critical value. If this is the case,
Bernoulli’s equation cannot be used.

Answer 36

turbulent

Question 37

The product is the volume _________, the rate at which volume crosses a section of the tube: Av = delta V / delta t

Answer 37

flow rate

Question 38

The speed of water spraying from the end of a garden hose _________ as the size of the opening is decreased with the thumb.

Answer 38

increases

Question 39

The principle states that “the pressure of a fluid [liquid or gas] decreases as the speed of the fluid increases.

Answer 39

Bernoulli’s principle

Question 40

Within the same fluid (air in the example of aircraft moving through air), high-speed flow is associated with low pressure, and low-speed flow is associated with high pressure.

Answer 40

Bernoulli’s principle

Question 41

states that the work done on a unit volume of fluid by the surrounding fluid is equal to the sum of the changes in kinetic and potential energies per unit volume that occur during the flow

Answer 41

Bernoulli’s principle

Question 42

is the principle that allows wings to produce lift and planes and helicopters to fly. There are many factors that can effect the lift produced under this principle, but in order to fully understand how and why things can effect flight one must understand how Bernoulli’s principle works.

Answer 42

Bernoulli’s Principle