Units of Measurements and
Uncertainty
Objectives:
• 1. Identify the metric units of measurement for length,
mass, and volume.
• 2. List the common metric prefixes and demonstrate how
metric prefixes can be used to change units
• 3. Explain why measuring always involves estimation.
• 4. Describe two causes of uncertainty in measurements.
• 5. Explain the difference between accuracy and precision.
Key Terms:
metric system, International System of Units (SI), base unit,
mass, derived unit, volume, metric prefix, precision, accepted
value, accuracy
• Measurements are required for scientific
inquiry. In order to have meaning a unit must
be attached to the measurement. Throughout
the different scientific disciplines you will find
the use of the metric system. Becoming
familiar with the standard prefixes will make
solving equations and converting units easier.
Metric Prefixes
Prefix
exa-
Prefix Symbol
E
Meaning
Scientific Notation
1,000,000,000,000,000,000 1018
peta-
P
1,000,000,000,000,000
1015
teragigamegakilohectodekameter
decicentimillimicronanopicofemtoatto-
T
G
M
k
h
da
1,000,000,000,000
1,000,000,000
1,000,000
1,000
100
10
1
0.1
0.01
0.001
0.000001
0.000000001
0.000000000001
0.000000000000001
0.000000000000000001
1012
109
106
103
102
101
100
10-1
10-2
10-3
10-6
10-9
10-12
10-15
10-18
d
c
m
m
n
p
f
a
SI Units
The units used in science are those primarily used throughout
the world. The International System of Units (SI) is a system
based on the metric system. There are 7 fundamental units of
measure
Name
Symbol
length (distance) l (d)
mass
m
time
t
electric charge Q
temperature
T
amount of a
n
substance
Unit of Measure
meter
kilogram
second
coulomb
Kelvin
mole
Unit Symbol
m
kg
s
C
K
mol
Unit Dimensions
m
kg
s
C
K
mol
English to Metric Conversions:
Distance
1km = 0.62 mi
Mass
1kg = 2.2lbs
Volume
3.744L = 1 gal
1m = 39.37in
907.185kg = 1ton 1 L = 1.06qt
1m = 1.0963yd 28.3g = 1oz
250ml = 1c
1cm = 0.39370in 453.59g = 1lb
Pressure / Energy Temperature
oC = 5/9 (oF-32)
101,325Pa =
1atm
oK = oC + 273
4.184J = 1cal
Other SI units derived from the base
units
Name
acceleration
Symbol
a
area
capacitance
density
A
C
D
electric current I
electric field
E
intensity
electric resistance R
Unit of Measure Unit Symbol
meter per second m/s2
squared
square meter
m2
Farad
F
kilogram per cubic kg/m3
meter
Ampere
A
Newton per
N/C
coulomb
Ohm
d
Unit Dimensions
m/s2
Volt
V
Joule
J
Newton
N
hertz
Hz
Joule
J
lumens per square lx
meter
Henry
H
lumen
lm
Weber
Wb
Tesla (weber per T
square meter)
Volt
V
kg*m2/C*s2
kg*m2/s2
kg*m/s2
s-1
kg*m2/s2
cd/m2
m2
C2*s2/kg*m2
kg/m3
C/s
kg*m/C*s2
kg*m2/C2*s
emf
energy
force
frequency
heat
illuminance
x
E
F
f
Q
E
inductance
luminous flux
magnetic flux
magnetic flux
density
potential
difference
power
pressure
L
F
f
B
P
p
Watt
W
Pascal (Newton Pa
per square meter)
kg*m2/s3
kg/m*s2
velocity
v
meters per secondm/s
m/s
volume
work
V
W
cubic meter
Joule
V
m3
J
kg*m2/C2
cd
kg*m2/C*s
kg/C*s
kg*m2/C*s2
m3
kg*m2/s2
Some commonly used values in
science.
Speed of light in a vacuum
Speed of sound
Acceleration due to Gravity
Average Earth - Sun distance (1 AU)
Average Earth - moon distance
Average radius of the Sun
Average radius of Jupiter
Average radius of Earth
Average radius of the moon
Average radius of the hydrogen atom
Mass of the Sun
Mass of Jupiter
Mass of Earth
Mass of the moon
Proton mass
Neutron mass
Electron mass
Atomic mass unit (amu)
Electron charge
Avogadro's number
Planck's constant (h)
Gas constant (R)
Molar volume of gas
2.9979 x 108 m/s
330 - 350 m/s (depending on temperature)
9.8 m/s2
1.50 x 1011 m
3.84 x 108 m
6.96 x 108 m
6.99 x 107 m
6.37 x 106 m
1.74 x 106 m
~5 x 10-11 m
1.99 x 1030 kg
1.90 x 1027 kg
5.98 x 1024 kg
7.35 x 1022 kg
1.6726 x 10-27 kg
1.6749 x 10-27 kg
9.11 x 10-31 kg
1.66054 x 10-27 kg
1.6 x 10-19 C
6.02 x 1023
6.6262 x 10-34 J-s
0.08206 atm-L/mol-K
22.4L