Cabal màssic: diferència entre les revisions

InEn elementary[[mecànica classicalclàssica]] mechanicselemental, massel flowcabal ratemàssic isapareix encounteredquan whenes dealingtreballa withamb [[variable-masssistema system|objectsde ofmassa variable|objectes massde massa variable]] com, suchper asexemple, aun rocketcoet ejectingque spentdesprèn fuelcombustible. OftenSovint, descriptionsles ofdescripcions suchd'aquest tipus d'objectes objectsinvoquen erroneouslyerròniament<ref name="Halliday">{{cite book|last=Halliday|coauthors=Resnick|title=Physics|volume=1|pages=199|quote=It is important to note that we ''cannot'' derive a general expression for Newton's second law for variable mass systems by treating the mass in '''F''' = ''d'''''P'''/''dt'' = ''d''(''M'''''v''') as a ''variable''. [...] We ''can'' use '''F''' = ''d'''''P'''/''dt'' to analyze variable mass systems ''only'' if we apply it to an ''entire system of constant mass'' having parts among which there is an interchange of mass.|isbn=0-471-03710-9}} [Emphasisèmfasi ascom in thea l'original]</ref> invokela [[Newton'ssegona secondllei lawde Newton]] '''F'''&nbsp;=d(''m'''''v''')/d''t'' bytractant treatingla both the massmassa ''m'' andi thela velocityvelocitat '''v''' ascom time-dependentvariables anddependents thendel applyingtemps thei derivativellavors productaplicant rulela regla de la derivada del producte. ALa correctdescripció descriptioncorrecte ofd'aquests suchobjectes anrequereix objectl'aplicació requiresde thela applicationsegona ofllei de Newton's secondal lawsistema tosencer thei entire,de massa constant-mass systemque consistingconsisteix oftant bothen thel'objecte objectcom anden itsla ejectedmassa massexpulsada.<ref name="Halliday" />