Download Review for Spring Semester Final

Principle of Technology
Review for Spring Semester Final
1.1 Forces in Mechanical Systems
 A force is a push or a pull.
 Force is a vector. It has both magnitude and
direction. Its magnitude is measured in
pounds or Newtons.
 Newton’s first law says that an object will
remain at rest or will continue in a straight
line unless it is acted on by a net force.
 Unbalance forces result in net force acting
on an object. Balance forces result in no net
force acting on an object.
 If two forces act on an object and the forces
act in a straight line, the magnitude of the
resultant is either the sum or the difference
between the two forces magnitudes.
 If two forces on an object do not act in a
straight line, the resultant can be found using
the head-to-tail method of vector addition.
 The mass of an object is a measure of the
object’s inertia. The weight is a measure of
the force exerted on the object by gravity.
 A torque is exerted on a body when a force
is applied and the line of action of the force
does NOT pass through the body’s axis of
rotation. The torque equals the force times
the lever arm.
 If not net torque is exerted on a on a body, it
will remain at rest or it will continue to
rotate at a constant rate.
1.2 Pressure in Fluid Systems
 Matter can exist in fours states: solid, liquid,
gas and plasma. Liquids and gases are
called fluids.
 The density of a substance is its mass per
unit volume. The density of water is 1
g/cm3.
 Weight density is weight per unit volume.
 Pressure is force divided by area over which
the force acts. We treat pressure as a scalar.
In SI units, pressure is measured in Pascals,
where 1 Pa = 1 N/m2.
 Pressure increases with depth of a fluid. For
a given fluid, the pressure does not depend
on the size or shape of the container.
 When an object is submerged in a fluid, an
upward force is exerted on the object caused
by the pressure difference between




the top and bottom of the object. The force is
called buoyant force.
The buoyant force exerted on an object equals
the weight of the fluid displaced by the object.
A pressure applied to a confined fluid is
transmitted throughout the fluid.
Atmospheric pressure is caused by the weight
of the air above a given area. Atmospheric
pressure can be measured with a barometer.
Absolute pressure is the s um of the gage
pressure and atmospheric pressure.
1.3 Voltage in Electrical Systems
 Newton’s law of universal gravitation and
Coulomb’s law are both inverse square laws.
The magnitude of both forces decreases with
the square of the distance between the masses
and the charges.
 Atoms are composed of protons, neutrons, and
electrons. Protons are positively charged,
electrons are negatively charged, and neutrons
have no charge.
 The flow of electrons in an electrical system is
a current.
 Unlike charges attract; like charges repel.
 An electric field is a model of the alteration of
space around one or more charges. You can
use the field to predict the force exerted on a
charge placed in the field.
 The potential difference, or voltage, between
two points in a uniform electric field is the
product of the field strength and the distance
between the points.
 Voltage is the prime mover in electrical
systems.
 A battery is a source of DC voltage. It can
maintain a current in an electrical circuit.
 Batteries or cells can be connected in series to
increase voltage.
1.4 Temperature in Thermal Systems
 The thermal energy of a body is the total
kinetic energy of motion all the particles that
make up the body.
 The temperature of a body is determined by
the average kinetic energy of the particles that
make up the body.
 A thermometer measures the temperature in
degrees Celsius or degrees Fahrenheit.
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


Heat is energy that flows from one body to
another because of a temperature difference.
Whenever two bodies are brought together,
heat flows from the body with the higher
temperature to the body with the lower
temperature.
The amount of heat transferred to an object
varies linearly with the object’s temperature
change, as long as there is no change of
state: Q = mTC.
If heat is transferred to a substance and it
changes state, its temperature does not
change.
2.1 Work in Mechanical Systems
 Mechanical systems use force and torque to
cause desired movement--and do useful
work.
 Work is done when a force or torque moves
an object. Work is done only while the
force or torque is applied in the direction of
movement.
 Work equals force times displacement or
torque time the angle. Work is measured in
ftlb or
Nm (= J). (W = Fd; W = )
 The displacement used to calculate work is
the distance the object moves while the
force is applied.
 Efficiency describes how well a machine
performs work. Efficiency is the ratio of
output worj to input work. (Eff = Wout/Win)
 Angle can be measured in either radians or
degrees. The radian is a dimensionless unit
and us used in most calculations involving
angles.
Other Units
Quantity
Force or Weight,
F or W
Torque, 
Work, W
Density, 
Weight Density,
w
Pressure, P
ftlb
ftlb
slugs/ft3
lb/ft3
lb/ft2 or psi (lb/in2)
Charge, q
Electric Field, E
Electric Potential
Difference, V
Heat, Q
Specific Heat, C
-
Heat of
Formation, Hf
Heat of
Vaporization, Hv
-
cal/g, or J/g
SI Prefixes
Prefix
kilo- (k-)
hecta- (h-)
deka- (da-)
base unit
deci- (d-)
centi- (c-)
milli- (m-)
-
Factor
1000
100
10
1
0.1
0.01
0.001
Exponent Form
103
102
101
100
10-1
10-2
10-3
Conceptual Equations
Pythagorean Theorem
c2  a2  b2
Trigonometry Functions
sin  
opp
hyp
F  ma
Amount of Substance,
n
Luminous Intensity, Iv
SI Unit
Newton (N, or
kgm/s2)
Nm (Joule, J)
Nm (Joule, J)
g/cm3
N/m3
Pascal, Pa (=
N/m2)
Coulomb, C
N/C
Volt, V (Nm/C,
or J/C)
Nm (Joule, J)
cal/goC, or
J/goC
cal/g, or J/g
Force
Base Units
Quantity
Length, l / Distance, d
Mass, m
Time, t
Electric Current, I
Temperature, T
English
pound (lb)
English Unit
foot (ft)
slug
second (s)
degree
Fahrenheit (oF)
-
SI Unit
meter (m)
kilogram (kg)
second (s)
ampere (A)
Kelvin (K)
Net Force
mole (mol)
Torque
-
candela (cd)
Fnet   F
Weight
W  mg
  FL
Density

m
V
cos  
adj
hyp
tan  
opp
adj
Weight Density
Work
W  F d
W
w 
V
Pressure
P
F
A
Pressure in a Fluid
P  w  h
Buoyant Force
Fbuoyant   w  Vobject  weight of fluid displaced
Pascal’s Principle (Formal for Hydraulic and Pneumatic
Systems)
Parea1  Parea2 or
F1 F2

A1 A2
Absolute Pressure
PAbsolute  PGage  PAtmospheric
Newton’s Gravitational Law
Fg  G
m1m2
d2
Coulomb’s Law
FE  K
q1 q 2
d2
Electric Field
F
E E
q
Electric Potential, or Voltage, or Electric Potential Difference
V  Ed
Converting Between Celsius and Fahrenheit
Tc 
5
TF  32
9
9
TF  TC  32
5
Heat Transfer without Phase Change
Q  mTC
Heat Transfer with Phase Change (Melting/Freezing)
Q  mH f
Heat Transfer with Phase Change
(Vaporization/Condensation)
Q  mH v
Quantity Symbols
Symbol Quantity
a, b, c
lengths of triangles sides (c = hypotenuse)
F
force
m
mass
a
acceleration
W
weight or work
g
acceleration due to gravity
torque

L
length of lever arm

density
V
volume
weight density

w
P
A
h
G
d
K
q
E
V
TC
TF
Q
T
C
Hf
Hv
pressure
area
fluid depth
universal gravitational constant
distance
Coulomb’s constant
charge
electric field
electric potential (also called voltage)
temperature in degrees Celsius
temperature in degrees Fahrenheit
heat transferred
change in temperature
specific heat
heat of formation
heat of vaporization
Some Constants and Equivalent Measures
g = 9.8 m/s2
-11
2
2
G = 6.67 x 10 Nm /kg
K = 9.0 x 109 Nm2/C2
qelementary = 1.60 x 10-19 C
1 m = 3.28 ft
1 slug = 14.59 kg
1 lb = 4.45 N
1 cal = 4.184 J
1 Cal = 1000 cal
1 atm = 760 mmHg = 101.3 kPa