Introduction to Engineering and Profession Ethics Lecture4-Fundamental Dimensions and Units- Dr.Khaled Bakro د. خالد بكرو

1. Lecture 4
Dr. Khaled Bakro
Fundamental Dimensions and Units
Introduction to Engineering
and Profession Ethics

2. PART 2 – ENGINEERING FUNDAMENTALS
—CONCEPTS EVERY ENGINEER SHOULD KNOW
In this chapter:
 we will explain fundamental engineering dimensions, such as length
and time, and their units, such as meter and second, and their role in
engineering.
 analysis and design. As an engineering student, and later as practicing
engineer.
 when performing an analysis, you will find a need to convert from one
system of units to another.
 We will explain the steps necessary to convert information from one
system of units to another correctly.
 we will also emphasize the fact that you must always show the
appropriate units that go with your calculations.
 Finally, we will explain what is meant by an engineering
system and an engineering component..
6- Fundamental Dimensions and Units

3. Engineering Problems and Fundamental Dimensions
when someone asks you how old you are, you reply by
saying “I am 19 years old.”
You don’t say that you are approximately 170,000 hours old
or 612,000,000 seconds old, even though these statements
may very well be true at that instant!

4. Engineering Problems and Fundamental Dimensions
fundamental or base dimensions to correctly express
what we know of the natural world. They are length,
mass, time, temperature, electric current, amount of
substance, and luminous intensity.

5. Systems of Units
The most common systems of units are :
 International System (SI) .
 British Gravitational (BG) .
 U.S. Customary units.

6. International System (SI) of Units (1)

7. International System (SI) of Units (2)

8. International System (SI) of Units (3)
The units for other physical quantities used in engineering
can be derived from the base units.
For example, the unit for force is the newton. It is derived
from Newton’s second law of motion.
One Newton is defined as a magnitude of a force that when
applied to 1 kilogram of mass, will accelerate the mass at a
rate of 1 meter per second squared (m/s2). That is: 1N
(1kg)(1m/s2).

9. International System (SI) of Units (4)

10. British Gravitational (BG) System (1)
In the British Gravitational (BG) system of units, the unit of
length is a foot (ft), which is equal to 0.3048 meter.
The unit of temperature is expressed in degree Fahrenheit (F)
or in terms of absolute temperature degree Rankine (R).
The relationship between the degree Fahrenheit and degree
Rankine is given by:

11. British Gravitational (BG) System (2)
The relationship between degree Fahrenheit and degree
Celsius is given by:
The relationship between the degree Rankine and the Kelvin
by:

12. Derived Units in Engineering

13. U.S. Customary Units (1)
The unit of length is a foot (ft), which is equal to 0.3048
meter.
The unit of mass is a pound mass (lbm), which is equal to
0.453592 kg; and the unit of time is a second (s).
The units of temperature in the U.S. Customary system are
identical to the BG system.

14. U.S. Customary Units (2)

15. Unit Conversion (1)
 Example 6.1 :
A person who is 6 feet and 1
inch tall and weighs 185 pound
force (lbf) is driving a car at a
speed of 65 miles per hour over
a distance of 25 miles. The
outside air temperature is 80F
and has a density of 0.0735
pound mass per cubic foot
(lbm/ft3). Convert all of the
values given in this example
from U.S. Customary Units to
SI units.

16. Unit Conversion (Example 6.1 )
1ft=12 in 1 ft = 0.3048 m 1lbf =4.448 N 1mile=5280 ft

17. Unit Conversion (cont. Example 6.1 )
1 lbm=0.453 kg

18. Unit Conversion (Example 6.2 )
Work out Example 6.2 at home .If you have any question ask
me .

19. Dimensional Homogeneity
What do we mean by “dimensionally homogeneous?”
Can you say, add someone’s height who is 6 feet tall to his
weight of 185 lbf and his body temperature of 98F?! Of
course not!

20. Dimensional Homogeneity (Example 6.3 )

21. For Equation 6.1 to be dimensionally homogeneous,
the units on the left-hand side of the equation must
equal the units on the right-hand side. This equality
requires the modulus of elasticity to have the units of
N/m2, as follows:
Dimensional Homogeneity (Example 6.3 )

22. Dimensional Homogeneity (cont. Example 6.3 )

23. Numerical versus Symbolic Solutions
 When you take your engineering classes, you need to be aware of
two important things:
(1) understanding the basic concepts and principles associated with
that class
(2) how to apply them to solve real physical problems (situations)
 Homework problems in engineering typically require either a
numerical or a symbolic solution.
 For problems that require numerical solution, data is given. In
contrast, in the symbolic solution, the steps and the final answer are
presented with variables that could be substituted with data.

24. Numerical versus Symbolic Solutions (Example 6.4)
Determine the load that can be lifted by the hydraulic system
shown. All of the necessary information is shown in the Figure.

25. Numerical versus Symbolic Solutions (Example 6.4)
Numerical Solution:
We start by making use of the given data and substituting
them into appropriate equations as follows.

26. Numerical versus Symbolic Solutions (Example 6.4)
Symbolic Solution:
For this problem, we could start with the equation that relates F2
to F1, and then simplify the similar quantities such as p and g in
the following manner:

27. Significant Digits (Figures)
 One half of the smallest scale division commonly is called the least
count of the measuring instrument.
 For example, referring to Figure 6.4, it should be clear that the least
count for the thermometer is 1F (the smallest division is 2F), for the
ruler is 0.05 in., and for the pressure gage is 0.5 inches of water.
 Therefore, using the given thermometer, it would be incorrect to
record the air temperature as 71.25F and later use this value to carry
out other calculations. Instead, it should be recorded as 71 1F.
 This way, you are telling the reader or the user of your
measurement that the temperature reading falls between 70F
and 72F.

28. Examples of recorded measurements

29. Significant Digits 2 (Figures)
Significant digits are numbers zero through nine. However,
when zeros are used to show the position of a decimal point,
they are not considered significant digits.
For example, each of the following numbers 175, 25.5, 1.85,
and 0.00125 has three significant digits. Note the zeros in
number 0.00125 are not considered as significant digits,
since they are used to show the position of the decimal point

30. Significant Digits 3 (Figures)
The number of significant digits for the number 1500 is not
clear. It could be interpreted as having two, three, or four
significant digits based on what the role of the zeros is.
In this case, if the number 1500 was expressed by 1.5 *10^3,
15*10^2, or 0.015 *10^5, it would be clear that it has two
significant digits. By expressing the number using the power of
ten, we can make its accuracy more clear.
However, if the number was initially expressed as 1500.0, then
it has four significant digits and would imply that the accuracy
of the number is known to 1/10000.

31. Significant Digits 4 (Figures)
 Addition and Subtraction Rules
 Multiplication and Division Rules

32. Engineering Components and Systems 1
 The primary function of a car is to move us from one
place to another in a reasonable amount of time. The car
must provide a comfortable area for us to sit within.
Furthermore, it must shelter us and provide some
protection from the outside elements, such as harsh
weather and harmful objects outside.
 The automobile consists of thousands of parts. When
viewed in its entirety, it is a complicated system.
Thousands of engineers have contributed to the design,
development, testing, and supervision of the manufacture
of an automobile.
 These include electrical engineers, electronic engineers,
combustion engineers, materials engineers, aerodynamics
experts, vibration and control experts, air conditioning
specialists, manufacturing engineers, and industrial
engineers.

33. Engineering Components and Systems 2
When viewed as a system, the car may be divided into major
subsystems or units, such as electrical, body, chassis, power
train, and air conditioning (see the following figure)
the electrical system of a car consists of a battery, a starter, an
alternator, wiring, lights, switches, radio, microprocessors,
and so on
each of these components can be further divided into yet
smaller components. In order to understand a system,
we must first fully understand the role and function
of its components.

34. An engineering System and its components

35. Engineering Components and Systems 3
During the next four or five years you will take a number of
engineering classes that will focus on specific topics.
You may take a statics class, which deals with the
equilibrium of objects at rest.
 You will learn about the role of external forces, internal
forces, and reaction forces and their interactions

36. Engineering Components and Systems 4
 Later, you will learn the underlying concepts and equilibrium
conditions for designing parts.
 You will also learn about other physical laws, principles,
mathematics, and correlations that will allow you to analyze,
design, develop, and test various components that make up a
system.
 It is imperative that during the next four or five years you fully
understand these laws and principles so that you can design
components that fit well together and work in harmony to fulfill the
ultimate goal of a given system

37. Physical Laws and Observations in Engineering 1
The key concepts that you need to keep in the back of your
mind are the physical and chemical laws and principles and
mathematics.
we use mathematics and basic physical quantities to express our
observations in the form of a law. Even so, to this day we may
not fully understand why nature works the way it does. We just
know it works.

38. Physical Laws and Observations in Engineering 2
There are physicists who spend their lives trying to understand
on a more fundamental basis why nature behaves the way it
does.
 Some engineers may focus on investigating the fundamentals,
but most engineers use fundamental laws to design things.
 Engineers are also good bookkeepers.

39. Physical Laws and Observations in Engineering 3
 To better understand this concept, consider the air inside a car tire. If
there are no leaks, the mass of air inside the tire remains constant.
This is a statement expressing conservation of mass, which is based
on our observations.
 If the tire develops a leak, then you know from your experience that
the amount of air within the tire will decrease until you have a flat
tire. Furthermore, you know the air that escaped from the tire was
not destroyed; it simply became part of the surrounding atmosphere.
 The conservation of mass statement is similar to a bookkeeping
method that allows us to account for what happens to the mass in an
engineering problem.

40. Physical Laws and Observations in Engineering 4
Conservation of energy is another good example. It is again
similar to a bookkeeping method that allows us to keep track
of various forms of energy and how they may change from
one form to another.
Another important law that all of you have heard about is
Newton’s second law of motion.
Newton expressed his observations using mathematics, but
simply expressed, this law states that unbalanced force is
equal to mass times acceleration.

41. Physical Laws and Observations in Engineering 5

42. Learning Engineering Fundamental Concepts and Design
Variables from Fundamental Dimensions

43. SUMMARY
 You should understand the importance of fundamental
dimensions in engineering analysis. You should also understand
what is meant by an engineering system and an engineering
component. You should also realize that physical laws are based
on observation and experimentation.
 You should know the most common systems of units: SI, BG,
and U.S. Customary.
 You should know how to convert values from one system of units
to another.
You should understand the difference between numerical
and symbolic solutions.