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on’s _____ Law: If a net force F net acts on an object of mass object’s acceleration a will be: a = Net forces ___________________ mass ________________________ F net a m a are: a = Δv/t is a _________________ o a = F net /m tells the______________ of a cause accelerations resists acceleration 2 nd F net m

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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 ,

Newton’s _____ Law:

If a net force Fnet acts on an object of mass m,the object’s acceleration a will be:

a = Net forces ___________________

mass ________________________

Fnet

a

m

a

Compare: a = Δv/t is a _________________ of a

a = Fnet/m tells the______________ of a

cause accelerations

resists acceleration

2nd

Fnet

m

Newton’s _____ Law:

If a net force Fnet acts on an object of mass m,the object’s acceleration a will be:

a = Net forces ___________________

mass ________________________

Fnet

a

m

a

Compare: a = Δv/t is a _________________ of a

a = Fnet/m tells the______________ of a

direct inverse

cause accelerations

resists acceleration

2nd

Fnet

m

definition

cause

1/ Units: a =

Fnet =

units: [N] =

[N] =

derived fundamental

1 N = the _____________ that produces an acceleration

of __________ when applied to a mass of _________

1 kg1 N

frictionless surface

[kg] [m/s2]

[kg m/s2]

1 m/s2 1 kg.

Fnet

mm a

net force

2/ a is a vector: a = 5.0 m/s2, east

magn. dir.

a/ The magnitude of a is also called the________________________.

vector magnitude

displacement distance

velocity speed

acceleration acceleration

acceleration

Ex. Names of vectors and their magnitudes.

Fnet.

w

w

w

w

w

9.81 m/s2

b/ The direction of a is ________________ the direction of 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).

g

the same as

downw

≠≠

3/ Compare:

a = __________

F's are ___________________________________

Newton’s 1st Law: Newton’s 2nd Law:

FN = 20N

w = 20 N

pull= 10N

Ff = 10 N

a = ___ ___________ v or v = ______

F's are _______________________________

FN = 20N

w = 20 N

pull= 10NFf = 2 N

Fnet = __________ Fnet = __________0 8N, right

0 not zero

balancedequilibrium

unbalancednon-equilibrium

constant0

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.

2.0kg

FN = 19.6 N

(2.0 kg)(9.81 m/s2)

push= 16N

Fnet =

______________

or ___________

+16 N 2.0 kg

+8 N kg

+ 8 m s2

16 N, right+ 16 N

a = Fnet

m

= = =

19.6 kgm/s2 19.6 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.

2.0kg

FN = 19.6 N

w = 19.6 N

pull= 16 N

Now, Fnet = ____________

a = Fnet

m

= +12 N 2.0 kg

= + 6 N kg

= + 6 m s2

Ff =4.0 N

a is _________ now b/c Fnet is___________ .

+ 12 N

less less

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 ____ .

2.0kg

Case 1: positive v

vi

2.0kg

Fnet

vf ___ vi so v = vf - vi ___ 0 and so a = v/t __ 0

2.0kg

vi

2.0kg

Fnet

Case 2: negative v

In both cases, Fnet is ________, so v and a are ________

but, in Case 2, v is ________________ .

Can’t tell. to the right v v

vf

vf

>

pos. pos.

negative

> >

vf ___ vi so v = vf - vi ___ 0 and so a = v/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.

2.0kg

FN = 19.6 N

w = mg

Ff

= 2N

Fnet = __________

= ________

a = Fnet

m

= -2 N 2.0 kg

= -1 N kg

= -1 m s2

2 N, left

-2 N= 19.6 N

The box is _________________ , because Fnet and v are in ______________________________ .

slowing downopposite directions

v

Ex: Why do all objects fall with same acceleration in free fall (no air resistance)?

small mass

big mass:

a =

Newton's2nd Law :

Fnet

Which object gets pulled down with a greater force?

Which object resists more?

Which accelerates most?

w wmm

m

a = a =mw

= =wm

small force

small inertia

= 9.81 m/s2

big force

big inertia

= 9.81 m/s2

bigbig

neither

Ex. A block is pulled along a frictionless table by a force that makes an angle to the horizontal.

2.0kg

F

w = 19.6 N

FN

a/ Find the x- and y-________________ of F.b/ Replace F in the free body diagram with them:

Fx =

FFy =

FN

Fy

Fx

w

F

balanced

unbalanced

components

Fcos

Fsin

What will happen to a if is increased?

y-direction: Because the block is not acceleratingup or down, the y-forces are ________________.

equilibrium: w =

x-direction: Only 1 force _________________

ax =

Fx

F

Fy

Fx ___creases, so a _____________________.

F

Fy

inc

balanced

Notice: w _____ FN

FN + Fy

unbalanced

Fx/m = Fcos/m

Fx

dealso

decreases