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

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.

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

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  1. 2nd Newton’s _____ Law: If a net force Fnet acts on an object of mass m, the object’s acceleration a will be: cause accelerations Fnet Net forces ___________________ a = resists acceleration mass ________________________ m a a Fnet m Compare: a = Δv/t is a _________________ of a a = Fnet/m tells the______________ of a

  2. 2nd Newton’s _____ Law: If a net force Fnet acts on an object of mass m, the object’s acceleration a will be: cause accelerations Fnet Net forces ___________________ a = resists acceleration mass ________________________ m a a direct inverse Fnet m Compare: a = Δv/t is a _________________ of a a = Fnet/m tells the______________ of a definition cause

  3. Fnet m 1 N 1 kg 1/ Units: a = Fnet = m a [kg] [m/s2] units: [N] = [kg m/s2] [N] = fundamental derived 1 N = the _____________ that produces an acceleration of __________ when applied to a mass of _________ net force 1 m/s2 1 kg. frictionless surface

  4. 2/ a is a vector: a = 5.0 m/s2, east magn. dir. a/ The magnitude of a is also called the________________________. acceleration Ex. Names of vectors and their magnitudes.

  5. the same as b/ The direction of a is ________________ the direction of Fnet. Fnet. Ex: In free fall, the weight w equals ________ • What is the acceleration at • all five points shown? • magn.: a = __ = ___________ • dir.: __________ because it is • the same direction as ______. • The acceleration is ____ 0 at the top because Fnet ____ 0 • there (and everywhere else). w g 9.81 m/s2 down w w w ≠ ≠ w w

  6. 3/ Compare: Newton’s 1st Law: Newton’s 2nd Law: FN = 20N FN = 20N Ff = 10 N pull = 10N pull = 10N Ff = 2 N w = 20 N w = 20 N 0 8N, right Fnet = __________ Fnet = __________ constant a = ___  ___________ v or v = ______ F's are _____________ __________________ 0 not zero a = __________ F's are _______________ ____________________ 0 unbalanced balanced non-equilibrium equilibrium The First Law is really just a _____________________ of the Second Law that is true when ____________________ . special case Fnet = 0

  7. a = Fnet m 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. FN = 19.6 N push = 16N 2.0 kg Fnet = ______________ or ___________ (2.0 kg)(9.81 m/s2) w = mg = _________________ ≈ _____________ = _____ 16 N, right 19.6 kgm/s2 19.6 N + 16 N + 8 m s2 +8 N kg = +16 N 2.0 kg = = (to right)

  8. a = Fnet m Ex: Add a friction force of 4.0 N to the previous example. Again, draw all forces acting on the mass, find Fnet and find a. FN = 19.6 N Ff = 4.0 N pull = 16 N 2.0 kg w = 19.6 N Now, Fnet = ____________ + 12 N = +12 N 2.0 kg = + 6 N kg = + 6 m s2 less less a is _________ now b/c Fnet is___________ .

  9. Which way is the mass in the previous problem moving? ___________. Why? Because Fnetis to the right, a is _____ _______. But a only tells the direction of _______, not ____ . Can’t tell. to the right Dv v vi vf Case 1: positive v Fnet 2.0 kg 2.0 kg vf ___ viso Dv = vf - vi ___ 0 and so a = Dv/t __ 0 > > > vi vf Case 2: negative v Fnet 2.0 kg 2.0 kg vf ___ viso Dv = vf - vi ___ 0 and so a = Dv/t __ 0 < < < pos. pos. In both cases, Fnet is ________, so Dv and a are ________ but, in Case 2, v is ________________ . negative

  10. 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. a = Fnet m v FN = 19.6 N 2.0 kg Ff = 2N 2 N, left Fnet = __________ = ________ = 19.6 N w = mg -2 N = -2 N 2.0 kg = -1 m s2 = -1 N kg slowing down The box is _________________ , because Fnet and v are in ______________________________ . opposite directions

  11. Ex: Why do all objects fall with same acceleration in free fall (no air resistance)? big mass: Newton's 2nd Law: m small mass Fnet a = w m m w w small force big force w = a = = a = m m small inertia big inertia = = 9.81 m/s2 9.81 m/s2 Which object gets pulled down with a greater force? Which object resists more? Which accelerates most? big big neither

  12. Ex. A block is pulled along a frictionless table by a force that makes an angle q to the horizontal. F q 2.0 kg F FN w = 19.6 N components a/ Find the x- and y-________________ of F. b/ Replace F in the free body diagram with them: Fy FN F Fy = balanced Fsinq q Fx unbalanced Fcosq Fx = w

  13. y-direction: Because the block is not accelerating up or down, the y-forces are ________________. balanced FN + Fy equilibrium: w = Notice: w _____ FN ≠ unbalanced x-direction: Only 1 force _________________ ax = Fx/m = Fcosq/m What will happen to a if q is increased? F F Fx ___creases, so a ________ _____________. de Fy also Fy inc q q decreases Fx Fx

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