1. Units of Measurement

2. SI Units
Inches, feet, degrees Fahrenheit, and cups are NOT units used in science
There was a need to report data that could be used and reproduced easily by others
Developed in 1795
Systeme Internationale d’Unites
By using one system of units, scientists can quickly 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. Base Units 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
Base Units

5. Derived Units Are a combination of base units Example:
The unit for Volume is cubic meters (m3) is a derived unit
You can calculate volume by multiplying length x width x height or m x m x m which equals m3

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. Large
Metric Prefix
Small

8. Conversion Factors
Is a ratio of equivalent measurements that is used to convert a quantity expressed in one unit to another unit

9. Dimensional Analysis
A method of analysis used when there is not enough information to set up precise equations
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

10. 10 megawatts is equal to how many watts?
10 MW x 1,000,000 W = 10,000,000 W MW
20,000 milligrams is equivalent to how many grams?
20,000 mg x g = 20 g
,000 mg
Convert the height of Mount Everest (8,848 m) into kilometers
8,848 m x km = km or 8.8 km
,000 m

11. Precision & Accuracy
Precision is a gauge of how exact a measurement is
The more significant figures there are, the more precise the measurement
5.2 meters vs meters
Accuracy is the closeness of a measurement to the actual value of what is being measured
Actual value is 20 cm, are the following measurements accurate?
Measurement 1 = 19.5 cm
Measurement 2 = 10 cm
Measurement 3 = 21 cm