Units of Measurement

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

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

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

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

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

Large Metric Prefix Small

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

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 megawatts is equal to how many watts? 10 MW x 1,000,000 W = 10,000,000 W 1 1 MW 20,000 milligrams is equivalent to how many grams? 20,000 mg x 1g = 20 g 1 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 1,000 m

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 5.2345867 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