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Units of Measurement
SI Units • There was a need to report data that
could be reproduced by others o Metric system was developed in
1795 o Systeme Internationale d’Unites
• By using one system of units, scientists can readily interpret the results of one another
Base Units • A defined unit in
a system of measurements that is based on an object or event in the physical world
Quantity Unit Symbol Length meter m
Mass kilogram kg
Temperature kelvin K
Time second s
Amount of Substance
mole mol
Electric Current
ampere A
Luminous Intensity
candela cd
Derived Units • Are a combination of base
units
Quantity Unit Symbol Area square meter m2
Volume cubic meter m3
Liquid volume cubic decimeter dm3 = L
Density kilograms per cubic meter
kg/m3
Pressure pascal (kg/m*s2) Pa
Energy Joule (kg*m2/s2) J
Frequency hertz (1/s) Hz
Electric Charge coulomb (A*s) C
Speed meters per second m/s
Metric Prefixes • Indicates how many times
a unit should be multiplied or divided by ten
Prefix Symbol Meaning Multiply Unit By
giga- G billion (109) 1,000,000,000
mega- M million (106) 1,000,000
kilo- k thousand (103) 1,000
deci- d tenth (10-1) 0.1 centi- c hundredth (10-2) 0.01
milli- m thousandth (10-3) 0.001
micro- µ millionth (10-6) 0.000001
nano- n billionth (10-9) 0.000000001
Conversion Factors • Is a ratio of equivalent
measurements that is used to convert a quantity expressed in one unit to another unit • Will be used to complete your
dimensional analysis hw worksheet
Dimensional Analysis • A problem-solving method that uses the fact
that any number or expression can be multiplied by one without changing its value.
• Also called factor-label method or the unit factor method
• The unit factors are conversion factors o Example any two terms that describe the same or
equivalent “amounts” of what we are interested in o Ex: 1 inch = 2.54 centimeters o 1 meter = 100 centimeters o 1 km = 1,000 meters
• 10 megawatts is equal to how many watts? • 10 MW x 1,000,000 W = 10,000,000 W 1 MW • 20,000 milligrams is equivalent to how many grams? • 20,000 mg x 1g = 20 g 1,000 mg • Convert the height of Mount Everest (8,848 m) into
kilometers • 8,848 m x 1km = 8.848 km or 8.8 km 1,000 m
Precision & Accuracy • Precision is a gauge of how exact a
measurement is o The more significant figures
(reported digits) there are, the more precise the measurement
• Accuracy is the closeness of a measurement to the actual value of what is being measured