Safety Safety glasses or goggles required at all times in the lab No horseplay allowed Know the location of the nearest fire extinguisher fire exit emergency phone

Units and Dimensions Dimensions are our fundamental concepts of measure Mass Length Time Current …. Units are our method of expressing those measures pound kilogram second ampere

Units and Dimensions Some rules: To be correct, an equation must have the same units on left and right hand sides Only terms with like units can be added and subtracted Units can be multiplied and divided at will Arguments to exponentiation type functions (e, log, ln) must be dimensionless

Units and Dimensions = 11 6 feet + 5 inches = ? 6 seconds + 5 feet = ? 6 seconds / 5 feet = 1.2 seconds/foot

Units and Dimensions SI system Straight forward Self Consistent Nomenclature Dimensions & Units Length meter (m) Masskilogram (kg) Timesecond (s) Temperaturekelvin (K) Currentampere (A)

Units and Dimensions SI system Some derived characteristics Force Mass * Length Time 2 Newton (N) = 1 kg m s 2 PressureForce Area Pascal (Pa) = 1 N m 2

Units and Dimensions American Engineering System Based on historical usage Nomenclature is difficult Dimensions & Units Length foot (ft) Masspound (lb m ) Timesecond (s) TemperatureFahrenheit (F) Currentampere (A)

Units and Dimensions American Engineering System Some derived characteristics Force Mass * Length Time 2 Pound Force (lb f ) Pound Force = ft lb m s 2

In American Engineering system, have equivalence in magnitude between weight (a force) and mass But causes much confusion when doing balance, because units must be converted. Leads to origin of g c

g c is conversion factor to convert from fundamental units to derived force units g c = ft lb m s 2 lb f Remember: g c is a conversion constant to go from force in fundamental units (mass, length, time) to derived units (lb f, kg f, etc)

Units and Dimensions American Engineering System Some derived characteristics Pressure = Force Area Pressure (psi) = lb f in 2 Remember: Pressure is pound force not a pound mass per sq. in. (or sq. ft.)

Always label numbers with units Be consistent in units Either SI or American Watch Units and Conversions