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 QuantitySI derived unit (symbol)QuantitySI derived unit (symbol) Length Meter (mm, cm, m) Time Seconds (s) Volume Liters (mL, cm 3, m 3 ) Pressure Pascal (Pa, kPa) Mass Grams (g, kg, mg) Energy Joules (J) Density Mass per unit of volume Ex: g/mL, g/cm 3, kg/m 3 Amount of Substance Moles (mol) Temperature Kelvins (K), 0⁰C = 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.

PrefixAbbreviationValue (Base Unit) Kilometerkm1000 Hectometerhm100 Dekameterdam10 Base Unit (meter)meter1 Decimeterdm0.1 Centimetercm0.01 Millimetermm0.001 Micrometerµm Nanometernm

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--- pascal – grams/millileter--- meter – second--- kilogram – kilograms/cubic meter--- Kelvins

Concept Check What is the difference between mass and weight. What is the symbol and meaning of each prefix – milli---- deci- – nano---- 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 grams and a volume of 17.5 cm 3

Calculations What is the percent error of a measurement with the experimental value of grams and an accepted value of 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 1.00g/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 the three equations relating mass, volume, and temperature?

Practice A weather balloon is inflated to a volume of 2.2x10 3 L with 37.4 grams of He. What is the density of the helium in g/L? A plastic ball with a volume of 19.7cm 3 has a mass of 15.8 g. What is the density? Would this ball sink or float in a container of gasoline (d=0.66g/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 K