Units of Measurement

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

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

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

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 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

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 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