PurposeandEmphasis．MechanicsnotonlyiStheoldestbranchofphysicsbutwasandstillisthebasisforalloftheoreticalphysics．Ouantummechanicscanhardlybeunderstood，perhapscannotevenbeformulated，withoutagoodknowl．edgeofgeneralmechanics．Fieldtheofiessuchaselectrodynamicsborrowtheirformalframeworkandmanyoftheirbuildingprinciplesfrommechanics．Inshort．throughoutthemanymodemdevelopmentsofphysicswhereonefrequentlyturnsbacktOtheprinciplesofclassicalmechanicsitsmodelcharacterisfelt．ForthisreasonitisnotsurprisingthatthepresentationofmechanicsreflectstOsomeex
tentthedevelopmentofmodemphysicsandthattodaythisclassicalbranchoftheoreticalphysicsiStaughtratherdifferentlythanatthetimeofArnoldSore．merfeld，inthe1920s，oreveninthe1950s，whenmoreemphasiswasputonthetheoryandtheapplicationsofpartial—differenfialequations．Today．symmetriesandinvarianceprinciples，thestructureofthespace-timecontinuum，andthegeomet—ricalstructureofmechanicsplayanimportantrole．Thebeginnershouldrealizethatmechanicsisnotprimarilytheartofdescribingblock．and．tackles．collisionsofbilliardballs，constrainedmotionsofthecylinderinawashingmachine，orbi．cycleriding．Howeverfascinatingsuchsystemsmaybe，mechanicsisprimarilythefieldwhereonelearnstodevelopgeneralprinciplesfromwhichequationsofmotionmavbederived，tounderstandtheimportanceofsymmetriesforthedy-namics，and，lastbutnotleast，togetsomepracticeinusingtheoreticaltoolsandconceptsthatareessentialforallbranchesofphysics．