1. Units of Measurement

2. SI Units
There was a need to report data that could be reproduced by others
Metric system was developed in 1795
Systeme Internationale d’Unites
By using one system of units, scientists can readily interpret the results of one another

3. Base Units
A defined unit in a system of measurements that is based on an object or event in the physical world

4. 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

5. Derived Units
Are a combination of base units

6. kilograms per cubic meter
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

7. Metric Prefixes
Indicates how many times a unit should be multiplied or divided by ten

8. 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-
millionth (10-6)
nano- n
billionth (10-9)

9. 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

10. 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
Example any two terms that describe the same or equivalent “amounts” of what we are interested in
Ex: 1 inch = 2.54 centimeters
1 meter = 100 centimeters
1 km = 1,000 meters

11. 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 g = 20 g
1,000 mg
Convert the height of Mount Everest (8,848 m) into kilometers
8,848 m x km = km or 8.8 km
1,000 m

12. Precision & Accuracy
Precision is a gauge of how exact a measurement is
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