SI units

 Scientists throughout the world use the metric system  This allows for a standard system to be used in science throughout the world  We will use the metric system when we take measurements in the lab

 Mass (weight): kilograms (kg)  Length: meter (m)  Time: seconds (s)  Temperature: degrees celcius (⁰C)

 The SI system is a decimal system  Based on powers of 10  A prefix represents the relationship of that unit to the base unit  Example: 1 meter = 100 centimeters or 1 cm =.01 meters  A table of prefixes is provided on page 1032 of your book

 To convert from one SI unit to another, you need to know the relationship between the two units.  The table of prefixes will help identify this relationship.  As mentioned before 1 meter (m) = 100 centimeters (cm) or 1 cm =.01 m  Also 1 gram (g) = 100 centigrams (cg) or 1cg =.01 g

 Some important conversion factors:  Length: ◦ 1 cm =.01 m or 1 m = 100 cm ◦ 1 millimeters (mm) =.1 cm or 1 cm = 10 mm ◦ 1 mm =.001 m or 1 m = 1000 mm  Mass (weight): ◦ 1 milligram (mg) =.001 grams (g) or 1 (g) = 1000 (mg)

 To convert a measurement of 12.3 centimeters to meters, you use the conversion factor.  You could use either 1 cm =.01 m or 1 m = 100 cm  Example: 12.3 cm x 1m/100cm = m or 12.3 cm x 0.01m/1cm = m