Physical Quantities: Dimensions and Units

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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) Kelvin (K) and temperature* temperature Centigrade (degrees C) MKS: m2 area distance x distance CGS: cm2 distance x distance x 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) MKS: m/s (rate of change of distance/time position) CGS: cm/s acceleration (rate of change of an (distance/time)/time MKS: m/s2 object’s velocity with CGS: cm/s2 (i.e., distance/time2) respect to time) force (“push” or “pull” that can 2 change an object’s mass x acceleration MKS: kg x m/s motion) or (Newton) CGS: gm x cm/s2 (Note that weight is just a mass x 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 MKS: N/ m2 (collective force exerted force/area or (kg x m/s2)/m2 by random molecular col- or (Pascal) lisions against each unit of (mass x distance/s2)/ area of an object’s area surroundings) CGS: dyne/cm2 work MKS: Newton x m (force times distance over force x distance or kg x m2/s2 which the force is applied or or Pa x m3 to an object as the object mass x acceleration (Joule) moves under the influence x distance of the force); or CGS: dyne x cm energy pressure x volume or gm x cm2/s2 (the capacity to do work) (erg) energy/time MKS: J/s power or or N x m/s (energy transferred or force x distance/time or kg x (m/s2) x m/s gained or lost per unit or (Watt) time) force x velocity etc. CGS: erg/s (energy/time)/area energy flux or MKS: (J/s)/m2 (rate at which energy is or W/m2 transferred, absorbed, or force x lost per unit time per unit (distance/time)/area surface area) etc. CGS: (erg/s)/cm2 .

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