Newton'sSecondLaw
Newton'sfirstlawofmotionpredictsthebehaviorofobjectsforwhichallexistingforcesarebalanced.Thefirstlaw-sometimesreferredtoasthelawofinertia-statesthatiftheforcesactinguponanobjectarebalanced,thentheaccelerationofthatobjectwillbe0m/s/s.Objectsatequilibrium(theconditioninwhichallforcesbalance)willnotaccelerate.AccordingtoNewton,anobjectwillonlyaccelerateifthereisanetorunbalancedforceactinguponit.Thepresenceofanunbalancedforcewillaccelerateanobject-changingeitheritsspeed,itsdirection,orbothitsspeedanddirection.
Newton'ssecondlawofmotionpertainstothebehaviorofobjectsforwhichallexistingforcesarenotbalanced.Thesecondlawstatesthattheaccelerationofanobjectisdependentupontwovariables-thenetforceactingupontheobjectandthemassoftheobject.Theaccelerationofanobjectdependsdirectlyuponthenetforceactingupontheobject,andinverselyuponthemassoftheobject.Astheforceactinguponanobjectisincreased,theaccelerationoftheobjectisincreased.Asthemassofanobjectisincreased,theaccelerationoftheobjectisdecreased.
Newton'ssecondlawofmotioncanbeformallystatedasfollows:
Theaccelerationofanobjectasproducedbyanetforceisdirectlyproportionaltothemagnitudeofthenetforce,inthesamedirectionasthenetforce,andinverselyproportionaltothemassoftheobject.
Thisverbalstatementcanbeexpressedinequationformasfollows:
a=Fnet/m
Theaboveequationisoftenrearrangedtoamorefamiliarformasshownbelow.Thenetforceisequatedtotheproductofthemasstimestheacceleration.
Fnet=m*a
Inthisentirediscussion,theemphasishasbeenonthenetforce.Theaccelerationisdirectlyproportionaltothenetforce;thenetforceequalsmasstimesacceleration;theaccelerationinthesamedirectionasthenetforce;anaccelerationisproducedbyanetforce.TheNETFORCE.Itisimportanttorememberthisdistinction.Donotusethevalueofmerely"any'oleforce"intheaboveequation.Itisthenetforcewhichisrelatedtoacceleration.Asdiscussedinanearlierlesson,thenetforceisthevectorsumofalltheforces.Ifalltheindividualforcesactinguponanobjectareknown,thenthenetforcecanbedetermined.