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40
ChapterII
towardsdisruptionanddivisionexceedsthatwhichresidesinthe
continuum,thequickerwillitforceitswaydown;onlyiftheforce
oftheheavythingistheweaker,willitrideuponthesurface.6
Giventheabovecondition,itiseasytounderstandwhyAristotle
madeareservationabouttheoccurrenceofmotionincaseswherethe
weightofthemovedobjectincreases.Ifagivenweight,herepresum-
ablyunderstoodastheresistivefactor,weredoubled,inresultitcan
simplyexceedthemotiveforce.Consequently,theactingforcewould
notbeabletoovercometheresistanceandtheconditionthattheforce
mustexceedtheresistanceformotiontooccurwillnotbefulflled.Itis
worthnotingthatinthecontextofthediscussiononthevoidAristotle
specifcallyintroducedtheresistanceofthemedium,ratherthanthe
weightofthemovedbody,asthefactoropposingthemotiveforcein
localmotion.Therefore,hisfamousuequations”regardingthiskindof
motionappearedfrstinthePhysicsinthefollowingformulas:
[Thebody]A,then,willmovethroughBintimeC,andthrough
D,whichisthinner,intimeE(ifthelengthofBisequaltoD)in
proportiontothedensityofthehinderingbody.ForletBbewater
andDair;thenbyasmuchasairisthinnerandmoreincorporeal
thanwater,AwillmovethroughDfasterthanthroughB.Letthe
speedhavethesameratiotothespeed,then,thatairhastowater.
Thenifairistwiceasthin,thebodywilltraverseBintwicethe
timethatitdoesD,andthetimeCwillbetwicethetimeE.7
JohnMurdochandEdithSylla,inoneoftheirarticlesonthetopic,
havesuggestedthatAristotle’spurposewasnottoestablishthestrict,
mathematicallyconsistentrelationsbetweenfactorscorrelatedwith
localmotionandtoformulateulawsofmotion”.Intheiropinion
6Aristotle,OntheHeavens,IV,313b18-23,J.L.Stocks(transl.),[in:]uTheBasic
Worksł”,p.466.
7Aristotle,Physics,215a,1-9,Bk.IV,p.284.Itisworthnotingherethatthera-
tioofthedensityofairandwaterisgivenhereonpurelyspeculativegrounds.
Infacttheaveragedensityofairequals0.001225g/cm3,whilethedensityof
waterissimply1g/cm3,thereforewaterisca.816(!)timesmoredensethanair.
SeeURL=<https://en.wikipedia.org/wiki/Density-of-air>;URL=<https://
en.wikipedia.org/wiki/Properties-of-water#Density-of-water-and-ice>.