The Metric System and Units of Measurement Units

The Metric System and Units of Measurement

Units • After measuring a value, you MUST assign proper units!! • “Walk five in that direction” means nothing until you provide a unit. . . meters, feet, etc. • In science, we will use the Metric System or the SI system

The SI System, Units of Measurement Quantity SI derived unit (symbol) Length Meter (mm, cm, m) Time Seconds (s) Volume Liters (m. L, cm 3, m 3) Pressure Pascal (Pa, k. Pa) Mass Grams (g, kg, mg) Energy Joules (J) Density Mass per unit of volume Ex: g/m. L, g/cm 3, kg/m 3 Amount of Substance Moles (mol) Temperature Kelvins (K), 0⁰C = 273. 15 K

The SI System of Measurement • The SI System uses many prefixes to increase or decrease the size of the values • A KILOmeter is greater than a meter which is greater than a MILLImeter • The prefixes allow us to work with very large numbers or very small numbers while still working with manageable sized values.

Prefix Abbreviation Value (Base Unit) Kilometer km 1000 Hectometer hm 100 Dekameter dam 10 Base Unit (meter) meter 1 Decimeter dm 0. 1 Centimeter cm 0. 01 Millimeter mm 0. 001 Micrometer µm 0. 000001 Nanometer nm 0. 00001

Units of Mass / Weight • Mass is NOT weight • Review: What is mass? What is weight? ? • Mass uses units of grams, whiles weight is usually measured in pounds

Concept Check • Name the quantity measured by each of the following SI units and give the SI symbol of the unit. – mole – grams/millileter – second – kilograms/cubic meter --- pascal --- meter --- kilogram --- Kelvins

Concept Check • What is the difference between mass and weight. • What is the symbol and meaning of each prefix – milli– nano- --- deci--- centi-

Calculations • Calculate the volume of a book that is 21 cm tall, 12 cm wide, and 3. 5 cm thick • Calculate the density of a sample with a mass of 12. 51 grams and a volume of 17. 5 cm 3

Calculations • What is the percent error of a measurement with the experimental value of 18. 99 grams and an accepted value of 15. 890 grams?

Specific Gravity • Specific Gravity is a comparison of the density of a substance with the density of a reference substance, usually at the same temperature. • This “reference substance” is usually _______. • Specific Gravity = density of substance (g/cm 3) density of H 2 O (g/cm 3)

Specific Gravity • Specific Gravity = density of substance (g/cm 3) density of H 2 O (g/cm 3) • The specific gravity of a liquid can be measured using a device called a hydrometer • The density of H 2 O is 1. 00 g/cm 3 (at room temp), making a substances’ specific gravity equal to its own density at room temp.

Practice • How is density calculated? • What are three equations relating mass, volume, and density?

Practice • A weather balloon is inflated to a volume of 2. 2 x 103 L with 37. 4 grams of He. What is the density of the helium in g/L? • A plastic ball with a volume of 19. 7 cm 3 has a mass of 15. 8 g. What is the density? Would this ball sink or float in a container of gasoline (d=0. 66 g/cm 3)

Temperature Scales • The Temperature of an object determines the direction of heat transfer • Heat travels from ____ to ____. • All substances (except water) expand when heated and condense when cooled. What happens to the pressure? ?

HEAT THEM UP, SPEED THEM UP!!!

Temperature Scales • Fahrenheit • Celsius • Kelvin

Conversion Equations ⁰F = (⁰C * 9/5 ) + 32 ⁰C = (⁰F – 32 ) * 5/9 K = ⁰C + 273. 15 K