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Free Fall
The acceleration of
gravity (g) for objects
in free fall at the
earth's surface is 9.8
Galileo found that all
things fall at the same
Free Fall
The rate of falling
increases by 9.8 m/s
every second.
Height = ½ gt2
For example:
½ (9.8 )12 = 4.9 m
½(9.8)22 = 19.6 m
½ (9.8)32 = 44.1 m
½ (9.8)42 = 78.4 m
Free Fall
A ball thrown
will fall at the
same rate as a
ball dropped
Free Fall
A ball thrown into the
air will slow down, stop,
and then begin to fall
with the acceleration
due to gravity. When it
passes the thrower, it
will be traveling at the
same rate at which it
was thrown.
Free Fall
An object thrown upward at an angle to
the ground follows a curved path called
a parabola.
Air Resistance
• In air…
– A stone falls faster
than a feather
• Air resistance
affects stone less
• In a vacuum
– A stone and a
feather will fall at
the same speed.
Air Resistance
• Free Fall
– A person in free
fall reaches a
velocity of
around 54 m/s
– With a
terminal velocity
is only 6.3 m/s
• Allows a safe
Air Resistance
• Ideal angle for a projectile
– In a vacuum, maximum distance is at an angle of 45o
– With air resistance (real world), angle is less
• Baseball will go furthest hit at an angle of around 40o
First Law of Motion
The first law of
motion states: If
no net force acts
on it, an object at
rest remains at
rest and an object
in motion remains
in motion at a
constant velocity.
Inertia and Mass
Inertia is the apparent resistance
an object offers to any change in
its state of rest or motion.
Second Law of Motion
Newton's second law
of motion states: The
net force on an object
equals the product of
the mass and the
acceleration of the
object. The direction of
the force is the same as
that of the acceleration.
F = Ma
Second Law of Motion
A force is any
influence that
can cause an
object to be
1 newton  1 N  1 (kg)(m/s 2 )
Mass and Weight
• Weight
Definition: The force with which an object is
attracted by the earth’s gravitational pull
• Example: A person weighing 160 lbs is being pulled
towards the earth with a force of 160 lbs (712 N).
– Near the earth’s surface, weight and mass are
essentially the same
Weight  (mass)(acc eleration of gravity)
w  mg
Third Law of Motion
The third law of
motion states:
When one object
exerts a force on a
second object, the
second object exerts
an equal force in the
opposite direction
on the first object.
Third Law of Motion
Examples of the 3rd Law
Circular Motion
Centripetal force is the inward force exerted on an object
to keep it moving in a curved path.
Centrifugal force is the outward force exerted on the
object that makes it want to fly off into space.
Circular Motion
Circular Motion
833 N is needed to make this turn.
If he goes too fast, which wheels are likely to
come off the ground first?
Artificial Satellites
• The world's first artificial
satellite was Sputnik I, launched
in 1957 by the Soviet Union.
GPS-Global Positioning
Artificial Satellites
The escape speed is the speed
required by an object to leave the
gravitational influence of an
astronomical body; for earth this
speed is about 40,000 km/h.