UnitsUnit SystemsTimeLengthMassSI PrefixesOther UnitsDensityMatching UnitsConversion FactorsUnitsUnitsUnit SystemsUnit SystemsSystems set up fundamental units.Systems set up fundamental units.•British system - foot, pound, secondBritish system - foot, pound, second•Metric system - meter, kilogram, secondMetric system - meter, kilogram, secondTimeTimeThe unit of time originally was based on the day and The unit of time originally was based on the day and the year.the year.The second was 1/60 * 1/60 *1/24 of a day.The second was 1/60 * 1/60 *1/24 of a day.In the 20th century the second was measured based In the 20th century the second was measured based on the timing of atoms.on the timing of atoms.We now know that the day is getting longer and “leap We now know that the day is getting longer and “leap seconds” are added every few years.seconds” are added every few years.The SI unit of time is the The SI unit of time is the secondsecond (s) (s)LengthLengthThe oldest standards of length were based on the The oldest standards of length were based on the human body.human body.The metric system defined the meter in terms of the The metric system defined the meter in terms of the Earth: 1/10,000,000 from the pole to the equator.Earth: 1/10,000,000 from the pole to the equator.The meter is now defined in terms of the second and The meter is now defined in terms of the second and speed of light.speed of light.The SI unit of length is the The SI unit of length is the metermeter (m) (m)MassMassStandard weights have been maintained for Standard weights have been maintained for centuries.centuries.Weight and mass were thought to be the same.Weight and mass were thought to be the same.Now a standard 1 kilogram mass is kept in Paris.Now a standard 1 kilogram mass is kept in Paris.The SI unit of mass is the The SI unit of mass is the kilogramkilogram (kg) (kg)SI PrefixesSI PrefixesPrefixes on units are used to Prefixes on units are used to represent powers of ten.represent powers of ten.Prefixes denote powers of Prefixes denote powers of ten from ten from 18 to 18 to 18 in steps 18 in steps of three.of three.Example: a kilometer is 10Example: a kilometer is 1033 meters or 1000 meters. meters or 1000 meters. Most CommonMost Commonmicro (micro () 10) 10-6-6milli (m) 10milli (m) 10-3-3kilo (k) 10kilo (k) 1033mega (M) 10mega (M) 1066Common, but the power is Common, but the power is not a factor of three.not a factor of three.centi (c ) 10centi (c ) 10-2-2deci (d ) 10deci (d ) 10-1-1Other UnitsOther UnitsThere are other fundamental There are other fundamental units in SI. See units in SI. See NISTNIST..•ampere (A)ampere (A)•kelvin (K)kelvin (K)•mole (mol)mole (mol)•candela (cd)candela (cd)Derived units are built from Derived units are built from the fundamental units.the fundamental units.•area (marea (m22))•volume (mvolume (m33))•velocity (m/s)velocity (m/s)•acceleration (m/sacceleration (m/s22))•force (kg m/sforce (kg m/s22) or (N)) or (N)•energy (kg menergy (kg m22/s/s22) or (J)) or (J)DensityDensityMatter has mass and takes Matter has mass and takes up volume.up volume.The ratio of the mass to the The ratio of the mass to the volume is the volume is the densitydensity..Vm /Salt (solid): 2.165 x 103 kg/m3Water (liquid): 1.000 x 103 kg/m3Nitrogen (gas): 1.251 kg/m3Matching UnitsMatching UnitsConversion between units must be of the same type.Conversion between units must be of the same type.Length conversion:Length conversion:•1 in = 2.54 cm1 in = 2.54 cmTime conversion:Time conversion:•1 hr = 3.6 x 101 hr = 3.6 x 1033 s sNo conversion between different types of units.No conversion between different types of units.•1 in is not equivalent to some seconds1 in is not equivalent to some secondsConversion FactorsConversion FactorsA value is converted by applying the ratio of the A value is converted by applying the ratio of the conversion factors.conversion factors.•How many inches in 50. cm?How many inches in 50. cm?•50. cm (1 in / 2.54 cm) = (50. / 2.54) in = 20. in50. cm (1 in / 2.54 cm) = (50. / 2.54) in = 20. inMany conversion factors use scientific notation.Many conversion factors use scientific notation.•How many seconds in a year?How many seconds in a year?•1 yr (365 d/yr) (24 hr/d) (3.6 x 101 yr (365 d/yr) (24 hr/d) (3.6 x 1033 s/hr) = 31500 x 10 s/hr) = 31500 x 1033 s = s = 3.15 x 103.15 x 1077 s s