IB›IB Physics SL›Mind mapsA.2 Forces and momentumIB Physics SL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsNewton's lawsFirst: constant velocity unless resultant force actsSecond: F=ΔpΔtF = \frac{\Delta p}{\Delta t}F=ΔtΔp, or F=maF = maF=ma for constant massThird: equal, opposite, same type, on different bodiesContact forcesNormal force: perpendicular to the surfaceStatic friction: Ff≤μsFNF_f \le \mu_s F_NFf≤μsFNDynamic friction: Ff=μdFNF_f = \mu_d F_NFf=μdFNHooke's law: FH=−kxF_H = -kxFH=−kxViscous drag on sphere: Fd=6πηrvF_d = 6\pi\eta r vFd=6πηrvBuoyancy: Fb=ρVgF_b = \rho V gFb=ρVgMomentump=mvp = mvp=mv, a vectorImpulse J=FΔtJ = F\Delta tJ=FΔt = change in momentumLonger contact time → smaller average forceConserved if no resultant external forceForcesand momentumNkg m/sF=maF = maF=maCollisionsElastic: kinetic energy conservedInelastic: some kinetic energy transferred to other formsExplosion from rest: equal and opposite momentaLighter fragment gets larger speed, via Ek=p2/2mE_k = p^2/2mEk=p2/2mCircular motionDirection changes, so it is acceleratinga=v2r=ω2ra = \frac{v^2}{r} = \omega^2 ra=rv2=ω2rv=ωr=2πrTv = \omega r = \frac{2\pi r}{T}v=ωr=T2πrCentripetal force is the resultant, towards the centreExam tipsWeight and normal force are not a third-law pairTerminal speed in fluid: weight = buoyancy + dragMomentum is conserved in inelastic collisions tooNever draw centripetal force as an extra force