vmd教程 forces-tutorial

1TCLFORCES11x

Figure3:Relationshipsamongvariablesinthescriptrot-a.tclAngularacceleration.Angularaccelerationisgovernedbyan

equationanalogoustoNewton’sSecondLaw:

τ=Iω(1)

τistorque(analogoustoforce),ωistheangularacceleration,and

Iisthemomentofinertia(analogoustomass).Torqueisgivenby

τ=ρ×F

whereFistheforceandρisapositionvectorrelativetotherotation

axis(seeFig.3).Inourcase,weapplytheforceperpendicularto

theρvector,sothecrossproductsimpli esandweget

τ=ρF(2)

forthemagnitude.Forpointparticles,themomentofinertiais

simplyI=mρ2,wheremistheparticle’biningthis

withEqns.1and2andsolvingforF,weget

F=mωρ

fortheforceperparticletoachieveaspeci edangularacceleration.