Units of Measurement SI Units Inches feet degrees

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 Electric Current Luminous Intensity mole mol ampere A candela cd

Derived Units • Are a combination of base units • Example: – The unit for Volume is cubic meters (m 3) is a derived unit – You can calculate volume by multiplying length x width x height or m x m which equals m 3

Quantity Unit Symbol Area Volume Liquid volume square meter cubic decimeter m 2 m 3 dm 3 = L Density kg/m 3 Pressure kilograms per cubic meter pascal (kg/m*s 2) Energy Joule (kg*m 2/s 2) J Frequency Electric Charge hertz (1/s) coulomb (A*s) Hz C Speed meters per second m/s Pa

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