A.) Forwards
B.) Backwards
C.) Towards the ceiling
D.) Won’t move
E.) Towards the seats
33 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Where will I move on the cart?
A
.
)
Forwards
B.) Backwards
C.) Towards the ceiling
D.) Won’t move
E.) Towards the seats
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Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Types
Friction
Tension
Normal Force
Gravity
Weight
Magnetism
35 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Gravity
Pull directed toward a second body.
Free Fall

F
g
=
m
(

g
)
or
F
g
=
mg
36 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Gravity at rest
Gravity acts on bodies in rest
Free Fall

~
F
g
=

F
g
ˆ
j
=

mg
ˆ
j
37 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Weight
The weight W of a body is equal to the magnitude
F
g
of the
gravitation force on the body
F
net
,
y
=
ma
y
W

F
g
=
m
*
0
=
0
W
=
F
g
So, if gravity changes...
38 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Normal Force
When a body presses against a
surface, the sufarce deforms
and pushes on the body with a
normal force
~
F
N
perpendicular
to the surface
Free Fall
~
F
N

F
g
=
ma
y
~
F
N

mg
=
ma
y
~
F
N
=
m
(
g
+
a
y
)
(1)
39 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Tension
When a cord attached to a body is pulled tight with a force
~
T
away from the body.
Often assume the chord to be massless
40 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Friction
Resistance of a force attempting to slide a body over a surface
41 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Newton’s third law (demo)
Newton’s second law
when two bodies interact, the forces on the bodies from
eachother are always equal in magnitude and opposite in
direction.
42 / 45
Course Overview
Relative Motion
Newton’s First Law
Newton’s Second Law
Types of Forces
Newton’s Third Law
Examples
Newton’s third law (demo)
Normal force
~
F
N
=
~
F
g
This holds even if the table was moving!
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5.3.2. If an object is moving can you conclude there are forces acting on it?
If an object is at rest, can you conclude there are no forces acting on it?
Consider each of the following situations.
In which one of the following
cases, if any, are there no forces acting on the object?
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