nd 2 Newtons Law If a net force

nd 2 Newton’s _____ Law: If a net force Fnet acts on an object of mass m, the object’s acceleration a will be: a= Fnet cause accelerations Net forces __________ m resists acceleration mass ____________ a a Fnet Compare: a = Δv/t m is a _________ of a a = Fnet/m tells the_______ of a

nd 2 Newton’s _____ Law: If a net force Fnet acts on an object of mass m, the object’s acceleration a will be: a= a Fnet cause accelerations Net forces __________ m resists acceleration mass ____________ a direct inverse Fnet m definitionof a is a _________ cause of a a = Fnet/m tells the_______ Compare: a = Δv/t

1/ Units: a = Fnet = units: Fnet m ma [N] = [kg] [m/s 2] [N] = [kg m/s 2] derived fundamental net force that produces an acceleration 1 N = the _______ 1 m/s 2 when applied to a mass of _____1 kg. of _____ 1 N 1 kg frictionless surface

2/ a is a vector: a = 5. 0 m/s 2, east magn. dir. a/ The magnitude of a is also called acceleration the____________. Ex. Names of vectors and their magnitudes. vector magnitude displacement distance velocity speed acceleration

the same as the b/ The direction of a is ________ direction of Fnet. Ex: In free fall, the weight w equals ____ Fnet. What is the acceleration at all five points shown? 9. 81 m/s 2 magn. : a = __ =g ______ w w down because it is dir. : _____ the same direction as ______. w The acceleration is ____ 0≠ at the top because F ____ 0 ≠ w net w w there (and everywhere else).

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

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 = 16 N 2. 0 kg 2) (2. 0 kg)(9. 81 m/s w = mg = _________ 19. 6 kgm/s 2 = _____ 19. 6 N ≈ _______ Fnet = 16 N, right _______ + 16 N or ______ a = Fnet m = +16 N 2. 0 kg = +8 N kg +8 m = s 2 (to right)

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 2. 0 kg Ff = 4. 0 N w = 19. 6 N Now, Fnet = + 12 N ______ a = Fnet m pull = 16 N = +12 N 2. 0 kg =+6 N kg =+6 m s 2 less. a is _____ now b/c Fnet is______

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

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. v F = 19. 6 N N 2. 0 kg Ff = 2 N 2 N, left Fnet = _____ -2 N = ____ a = Fnet m = -2 N 2. 0 kg w = mg = -1 N kg = 19. 6 N = -1 m s 2 slowing down The box is _________ , because Fnet opposite directions and v are in _______________.

Ex: Why do all objects fall with same acceleration in free fall (no air resistance)? Newton's 2 nd Law : Fnet a= m small mass m w a= w m = small force small inertia a= = 9. 81 m/s 2 big mass: m w w m big force = big inertia = 9. 81 m/s 2 Which object gets pulled down with a greater force? big Which object resists more? Which accelerates most? neither big

Ex. A block is pulled along a frictionless table by a force that makes an angle q to the horizontal. F F FN q 2. 0 kg w = 19. 6 N components of F. a/ Find the x- and y-________ b/ Replace F in the free body diagram with them: F Fy = Fsinq q Fx = Fcosq FN Fy balanced w Fx unbalanced

y-direction: Because the block is not accelerating up or down, the y-forces are ________. balanced FN + F y 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 Fy q Fx F Fy inc q Fx Fx ___creases, de also so a ____ decreases _______.