Systems of Units Section 23 Physical Quantity Unit Abbreviation Mass Kilogram Gram CGS kg Length Meter Centimeter CGS m Time Second s Temperature Kelvin K Amount of substance ID: 644558
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Slide1
Dimensional Analysis
Chapter 2Slide2
Systems of Units
Section 2.3
Physical Quantity
Unit
Abbreviation
Mass
Kilogram
Gram (CGS)
kg
Length
Meter
Centimeter (CGS)
m
Time
Second
s
Temperature
Kelvin
K
Amount of substance
Mole
mol
Electric Current
Ampere
A
Luminous intensity
Candela
cdSlide3
Derived Units
Quantity
Unit
Symbol
Equivalent
in Terms of Base Units
Volume
liter
L
0.001 m
3
1000 cm
3
Force
newton
(SI)
dyne (CGS)
N
1 kg
∙ m/s
2
1 g
∙ cm/s
2
Pressure
pascal
(SI)
Pa
1 N/m
2
Energy, work
joule (SI)
erg (CGS)
gram-calorie
J
cal
1 N
∙ m = 1 kg ∙ m
2
/s
2
1
dyne
∙cm
= 1 g∙cm
2
/s
2
4.184 J = 4.184 kg
∙ m
2
/s
2
Power
watt
W
1 J/s = 1 kg
∙ m
2
/s
2Slide4
Section
2.2
Dimensional Analysis
Utilizes
conversion factors
in order to convert between units of one thing to units of something else
Examples of conversion factors:
1 foot = 12 inches
2.54 cm = 1 inchSlide5
Example
How many centimeters are in 1.39 feet?
Hint: 1 in = 2.54 cm
See Sample Exercise 1.9 (Pg. 25)
42.4 cmSlide6
Conversions Involving More than One Unit
The speed of sound in air at sea level is 340 m/s. Express this speed in miles per hour.
Hint: 1 mile = 1.6093 km
See Sample Exercise 1.10 (Pg. 26) and Useful Conversion Factors and Relationships (Inside back cover)
760 mile/hrSlide7
Conversions Involving Cubed Units
Express a density of 8.4 g/cm
3
in terms of SI base units (kg/m
3
).
See Sample Exercise 1.11 (pg. 27-28)
8400 kg/m
3
OR
8.4 x 10
3
kg/m
3Slide8
Combination
Carry out the following conversion:
0.04 g/min
∙ m
3
to
lb
m
/hr
∙ ft
3
1.5 x 10
-4
lb
m
/hr
∙ ft
3Slide9
For Super Duper Fun
In 1916
Nusselt
derived a theoretical relation for predicting the coefficient of heat transfer between a pure saturated vapor and a colder surface:
w
here
h
= mean heat transfer coefficient, Btu/(hr)(ft
2
)(
ºF)
k
= thermal conductivity, Btu/(hr)(ft)(
ºF
)
= density, lb/ft
3
g
= acceleration of gravity, 4.17 x 10
8 ft/(hr)2 = enthalpy change, Btu/lb L = length of tube, ft = viscosity, lbm/(hr)(ft) T= temperature difference, ºFWhat are the units of the constant, 0.943?Slide10
Assignments
Complete the following questions at the end of Chapter 2:
2.1, 2.2, 2.6, 2.8, 2.11