Standard Units of Measure
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The Standard Units
• SI units: Système International = International
System
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Mass vs Weight
• Mass: Measure of the amount of matter
present in an object (SI unit is kg)
– Commonly measure mass in grams (g) or
milligrams (mg)
• Weight: measures the gravitational pull on
an object (SI unit is N)
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Time
• Measure of the duration of an event
• SI units = second (s)
• 1 s is defined as the period of time it takes
for a specific number of radiation events
of a specific transition from cesium–133
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Temperature
• Measures the average amount of kinetic energy caused
by motion of the particles
• SI unit is kelvin (K), no
negative numbers
• higher temperature =
larger average kinetic
energy
( F  32)
C 
1.8
K  C  273.15
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Related Units in the SI System
• All units in the SI system are related to the
standard unit by a power of 10
• The power of 10 is indicated by a prefix
multiplier
• The prefix multipliers are always the same,
regardless of the standard unit
• Report measurements with a unit that is close
to the size of the quantity being measured
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Common Prefix Multipliers in the
SI System
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Prefixes to Memorize
Prefix
Symbol
Meaning
Value
kilo-
k
one thousand
1000
deci-
d
one tenth
1/10
centi-
c
one hundreth
1/100
milli-
m
one thousandth 1/1000
Examples:
1000 millimeters = 1 meter
100 centimeters = 1 meter
1 centimeter =
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meter = 0.01 meter
Volume
• Measure of the amount of space occupied
• (length) x (width) x (height)
• Commonly measured in liters (L),
milliliters (mL), or cubic centimeters (cm3)
• Commonly measure liquid or gas volume
in milliliters (mL)
• Relationship between mL and cm3
– 1 mL = 1 cm3
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Estimating the Last Digit
•
•
For instruments marked with a scale, you get
the last digit by estimating between the
marks
Mentally divide the space into ten equal
spaces, then estimate how many spaces over
the indicator the mark is
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Accuracy vs Precision
• Accuracy: how close a measurement comes to
the actual value
• Precision: how close repeated measurements
are to each other
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Accuracy vs. Precision
• Suppose three students are asked to determine
the mass of an object whose known mass is 10.00
g
• The results they report are as follows
Looking at the graph of the results shows that Student A is
neither accurate nor precise, Student B is inaccurate, but is
precise, and Student C is both accurate and precise.
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