METR 201: Physical Processes Dr. Dave Dempsey in the Atmosphere Physical Quantities: Dimensions and Units Quantities Dimensions MKS and CGS Units MKS: kilograms (kg) mass mass CGS: grams (gm or g) distance, depth, length, MKS: meters (m) height, width distance CGS: centimeters (cm) time time seconds (sec or s) temperature temperature Kelvin (K) and Centigrade (degrees C) MKS: m2 area distance × distance CGS: cm2 distance × distance MKS: m3 volume × distance 3 (i.e., distance3) CGS: cm mass/volume MKS: kg/m3 density (i.e., mass/distance3) CGS: gm/cm3 speed; velocity (motion) (rate of change of distance/time MKS: m/s position) CGS: cm/s acceleration (distance/time)/time (rate of change of an MKS: m/s2 2 object’s velocity with 2 CGS: cm/s respect to time) (i.e., distance/time ) force (“push” or “pull” that can MKS: kg × m/s2 change an object’s mass × acceleration motion) or (Newton) CGS: gm × cm/s2 (Note that weight is just a mass × distance/time2 special case of a force— (dyne) the force of gravity) 1 METR 201: Physical Processes Dr. Dave Dempsey in the Atmosphere Quantities (cont’d) Dimensions MKS and CGS Units pressure force/area MKS: N/ m2 (collective force exerted or 2 2 by random molecular col- (mass or (kg × m/s )/m (Pascal) lisions against each unit of × distance/time2)/area area of an object’s or 2 surroundings) energy/volume CGS: dyne/cm work MKS: Newton x m (force times distance over force × distance or kg × m2/s2 which the force is applied or or Pa × m3 to an object as the object mass × acceleration (Joule) moves under the influence × distance of the force); or CGS: dyne × cm energy pressure × volume or gm × cm2/s2 (the capacity to do work) (erg) energy/time MKS: J/s power or or N × m/s (energy transferred or force × distance/time or kg × (m/s2) x m/s gained or lost per unit or (Watt) time) force × velocity etc. CGS: erg/s (energy/time)/area energy flux or MKS: (J/s)/m2 (rate at which energy is 2 transferred, absorbed, or force or W/m × (distance/time)/area lost per unit time per unit etc. CGS: (erg/s)/cm2 surface area) .