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2 nd. Newton’s _____ Law: If a net force F net acts on an object of mass m , the object’s acceleration a will be:. cause accelerations. F net. Net forces ___________________. a =. resists acceleration. mass ________________________. m. a. a. F net. m. - PowerPoint PPT Presentation

### Transcript of Newton’s _____ Law: If a net force F net acts on an object of mass m ,

• Newtons _____ Law: If a net force Fnet acts on an object of mass m,the objects acceleration a will be:a = Net forces ___________________mass ________________________FnetamaCompare: a = v/t is a _________________ of a a = Fnet/m tells the______________ of acause accelerationsresists acceleration2ndFnet m

• Newtons _____ Law: If a net force Fnet acts on an object of mass m,the objects acceleration a will be:a = Net forces ___________________mass ________________________FnetamaCompare: a = v/t is a _________________ of a a = Fnet/m tells the______________ of adirectinversecause accelerationsresists acceleration2ndFnet mdefinitioncause

• 1/ Units:a =Fnet =units:[N] =[N] =derivedfundamental1 N = the _____________ that produces an acceleration of __________ when applied to a mass of _________frictionless surface[kg] [m/s2][kg m/s2]1 m/s21 kg.m anet force

• 2/ a is a vector: a = 5.0 m/s2, eastmagn.dir.a/ The magnitude of a is also called the________________________.accelerationEx. Names of vectors and their magnitudes.

vectormagnitudedisplacementdistancevelocityspeedaccelerationacceleration

• Fnet.wwwww9.81 m/s2b/ The direction of a is ________________ the direction of Fnet.Ex: In free fall, the weight w equals ________What is the acceleration atall five points shown?magn.: a = __ = ___________dir.: __________ because it isthe same direction as ______.The acceleration is ____ 0 at the top because Fnet ____ 0there (and everywhere else).gthe same asdownw

• 3/ Compare:a = __________F's are ___________________________________Newtons 1st Law:Newtons 2nd Law:FN = 20Nw = 20 N pull= 10NFf = 10 Na = ___ ___________ v or v = ______F's are _______________________________FN = 20Nw = 20 N pull= 10NFf = 2 NFnet = __________Fnet = __________08N, right0not zerobalancedequilibriumunbalancednon-equilibriumconstant0 The First Law is really just a _____________________ of the Second Law that is true when ____________________ .special caseFnet = 0

• w = mg = _________________ _____________ = _____Ex: A force of 16 N pushes horizontally on a 2.0 kg mass on a frictionless surface. Draw all the forces acting on the mass. Then find Fnet and a.2.0kgFN = 19.6 N(2.0 kg)(9.81 m/s2) push= 16NFnet = ______________or ___________ +16 N 2.0 kg +8 N kg + 8 m s216 N, right+ 16 N===19.6 kgm/s219.6 N(to right)

• Ex: Add a friction force of 4.0 N to the previousexample. Again, draw all forces acting on the mass, find Fnet and find a.2.0kgFN = 19.6 Nw = 19.6 N pull= 16 NNow, Fnet = ____________= +12 N 2.0 kg= + 6 N kg= + 6 m s2Ff =4.0 Na is _________ now b/c Fnet is___________ .+ 12 Nlessless

• Which way is the mass in the previous problem moving? ___________. Why? Because Fnet is to the right, a is _____ _______. But a only tells the direction of _______, not ____ .2.0kgCase 1: positive vvi2.0kgFnetvf ___ vi so Dv = vf - vi ___ 0 and so a = Dv/t __ 02.0kgvi2.0kgFnetCase 2: negative vIn both cases, Fnet is ________, so Dv and a are ________ but, in Case 2, v is ________________ .Cant tell.to the rightDvvvfvf>pos.pos.negative>>vf ___ vi so Dv = vf - vi ___ 0 and so a = Dv/t __ 0
• Ex: A 2.0 kg box slides to the right over a surface with a constant frictional force of 2 N. Draw all forces acting on the mass, find Fnet and a.2.0kgFN = 19.6 Nw = mg Ff= 2NFnet = __________ = ________= -2 N 2.0 kg= -1 N kg= -1 m s22 N, left-2 N= 19.6 NThe box is _________________ , because Fnet and v are in ______________________________ .slowing downopposite directionsv

• Ex: Why do all objects fall with same acceleration in free fall (no air resistance)?small massbig mass:a =Newton's2nd Law :FnetWhich object gets pulled down with a greater force?Which object resists more?Which accelerates most?wwmmma =a =mw==wmsmall forcesmall inertia=9.81 m/s2big forcebig inertia=9.81 m/s2bigbigneither

• Ex. A block is pulled along a frictionless table by a force that makes an angle q to the horizontal.w = 19.6 NFNa/ Find the x- and y-________________ of F.b/ Replace F in the free body diagram with them:Fx =FFy = FNFyFxwFqbalancedunbalancedcomponentsFcosqFsinq

• What will happen to a if q is increased?y-direction: Because the block is not acceleratingup or down, the y-forces are ________________.equilibrium: w =x-direction: Only 1 force _________________ ax =FxFFyqFx ___creases, so a _____________________.FFyinc qbalancedNotice: w _____ FNFN + FyunbalancedFx/m= Fcosq/mFxdealsodecreases