1. It is absolutely essential to report units with the number answers.
Chapter 14
Units Conversions
This is truly a joint class between the instructors.
This may seem like a lot of slides for half of a class, but over half of them are quick lists that do not require much discussion.
The supplements fundamentalSI.ppt and gcderived.ppt are linked on the web, so students can access them that way.
Also, in an attempt to keep the students on task and avoid them doing the class exercises in advance, many of the numerical/unit values in the last two pairs exercises have been replaces with ‘?’ in the student version.
It is absolutely essential to report units with the number answers.

2. Unit History inch foot yard width of your thumb
originally the length of your foot, now greater
yard
three feet, from nose to middle finger

3. Unit History fathom mile furlong 6 feet, arm span
1000 paces, 5280 feet
furlong
220 yards

4. 14.7 Temperature Scales
Example:
T = 77 K

5. Mass the quantity of matter in an object
the measurement of the inertia
measured in kilograms (kg)

6. Weight the force upon an object due to gravity Fg = mg
Weight = Mass  Acceleration of gravity
Fg = mg
measured in Newtons (N) in the metric system or pounds (lb) in the British system

7. Engineering Mass and Weight
Pound-Mass
lbm
One pound-mass weighs 1 pound.
1 slug = 32.2 lbm
Pound-Force
lbf
It is the same as a pound (lb).
1 lbf = 1 lb

8. 1 lbf = 32.2 lbm ft/s2

9. In-class Assignment

10. Chapter 15

11. Dimensions Dimension Symbol Length Mass time force electric current
absolute temperature
luminous intensity
[L]
[M]
[T]
[F]
[A]
[q]
[/]

12. Fundamental Dimension
Base Units
Fundamental Dimension
Base Unit
time
electric current
absolute temperature
luminous intensity
amount of substance
second (s)
ampere (A)
kelvin (K)
candela (cd)
mole (mol)

13. The International System of Units (SI)
Fundamental Dimension
Base Unit
length [L]
mass [M]
time [T]
electric current [A]
absolute temperature [q]
luminous intensity [l]
amount of substance [n]
meter (m)
kilogram (kg)
second (s)
ampere (A)
kelvin (K)
candela (cd)
mole (mol)

14. What are these things?
See fundamentalSI.ppt for information about these 'things'

15. SI Prefixes Prefix Decimal Multiplier Symbol nano micro milli centi
deka
hecto
kilo
mega
giga
Prefix
Decimal Multiplier
Symbol
10-9
10-6
10-3
10-2
10-1
10+1
10+2
10+3
10+6
10+9 n m c d da h k M G

16. Supplementary SI Dimensions
Supplementary Dimension
Base Unit
plane angle
solid angle
radian (rad)
steradian (sr)

17. Force = (mass) (acceleration)

18. U.S. Customary System of Units (USCS)
Fundamental Dimension
Base Unit
length [L]
force [F]
time [T]
foot (ft)
pound (lb)
second (sec)
Derived Dimension
Unit
Definition
mass [FT2/L]
slug
lbf sec2/ft

19. Force = (mass) (acceleration)
F = ma
W = mg

20. American Engineering System of Units (AES)
Fundamental Dimension
Base Unit
length
mass
force
time
electric charge [Q]
absolute temperature
luminous intensity
amount of substance
foot (ft)
pound (lbm)
pound (lbf)
second (sec)
coulomb (C)
degree Rankine (oR)
candela (cd)
mole (mol)

21. Converting Between Foot and Meter
To convert from foot to meter, multiply by
3.048* E-01
To convert from meter to foot, multiply by
(3.048* E-01)-1

22. Thought Item
Concerning the previous slide, which of the following is true?
a. There are exactly m/ft.
b. There are exactly ft/m.
c. Neither a not b.
Hint: Think about this physically..
Answer: A

23. American Engineering System
Note, there is a problem when we use the same unit (“pound”, meaning lbf and lbm) to describe two different dimensions.
Newton's Second Law: F = ma
 1 lbf = 1 lbm ft/s2 ??? NO!!!
Must have conservation of units.

24. Conservation of Units Principle of conservation of units:
units on the left side of an equation must be the same as those on the right side of an equation
dimensional homogeneity

25. AES and Newton’s Law Must maintain dimensional homogeneity:
Now we have lbf = lbf
See gcderived.ppt for the derivation of gc

26. Pairs Exercise (5 min.) Use a different pairing...
The force of wind acting on a body can be computed by the formula:
F = Cd V2 A
where: F = wind force in lbf , Cd= drag coefficient (no units), V = wind velocity in miles per hour and A = projected area in ft2
Is this dimensionally homogeneous?
What are the dimensions of ?

27. Reality Check... Are units really important?
Is checking your work and your team’s work really important?
Mars Lander (ABC news)
Mars Lander (NASA)

28. Homework

29. Temperature Exercise
You take water from the faucet (80 oF) and bring it to a boil on the stove.
What is the temperature change in oC?
What is the initial temperature in oC?

30. A Solution
For the temperature change, the best solution process is to use degree equivalents

31. A Solution For the temperature value we use temperature conversion:
oC = (5/9)*( ) = 26.7 oC