Bellwork
When is the Newton Story / Comic
Board Project due?
 On Friday the thirteenth (12/13/13)

Newton 2nd Law Notes
12/9/13
Newton’s 2nd Law Lab
 From
Part 1:
1
a ~ — (inversely proportional)
m
If mass increases then acceleration
decreases.
Newton’s 2nd Law Lab
 From
Part 2:
a
F (directly proportional)
~
If force increases then
acceleration increases.
Newton’s 2nd Law Lab
Parts 1:
1
a ~ —
m
Part 2:
and
a
~
F
Newton’s 2nd Law Lab
 Putting
a
~
them together:
F
—
m
or
a
=
F
—
m
Newton’s 2nd Law of Motion
 Rearranging
a
=
F
—
m
the equation:
;
F
=
m·a
Newton’s 2nd Law
 This
nd
2
is Newton’s
Law
equation:
Fnet = m · a
Why an acceleration of g?


more mass = more force
less mass = less force
more mass = more inertia
(harder to move)
 less mass = less inertia
(easier to move)

F = ma
98 N = 10 kg x 9.8 m/s/s
F = ma
9.8 N = 1.0 kg x 9.8 m/s/
Draw on Board
 Different forces of
gravity
 Different masses
 YET, the same
acceleration of
gravity
Why an acceleration of g?

Newton’s 2nd Law proves that different
masses accelerate to the earth at the
same rate, but with different forces and
different inertias (masses).
Why an acceleration of g?
Same acceleration because:
 The force of gravity is directly
proportional to acceleration
 But, the mass is indirectly proportional
to acceleration
 And these balance out to the same rate
of acceleration

Equilibrium
Equilibrium (Forces): The state of
balance where no net forces act on an
object. (in equations, Fnet = 0 N)
 Constant velocity or speed means
equilibrium
 Equilibrium is not the same as
Newton’s 3rd Law
 Equilibrium acts on ONE object
 Where, Newton’s 3rd Law acts on TWO
objects

Ex) A student sitting in a chair

Equilibrium
 F.B.D.
Newton 3rd Law
1) Action: Earth pulling the
student down.
Reaction: Student pulling
the Earth up.
2) Action: Student pushing
on seat down.
Reaction: Seat pushing
student up.

Free Body Diagrams
Equations
Net Force
 Newton’s 2nd Law

Homework
Net Force, Friction and Weight
 Due on Wednesday 12/11/13
