Download Chapter 2 Forces In Motion

Chapter 6 Forces In
Motion
Section 1 – Gravity and
Motion
pp. 150 - 157
Terms to Learn
Air resistance – the fluid friction that
opposes the motion of objects through the
air
 Terminal velocity – the constant velocity of
a falling object when the size of the
upward force of air resistance matches the
size of the downward force of gravity

Terms to Learn
fall – the condition an object is in
when gravity is the only force acting
on it
 Projectile motion – the curved path an
object follows when thrown or
propelled near the surface of the
Earth
 Free
All objects fall with the same
acceleration

Objects fall to the ground at the same rate
because the acceleration due to gravity is
the same for all objects.
ACCELERATION DUE TO
GRAVITY
All objects accelerate toward earth at a
rate of 9.8 m/s every second, no matter
what the mass. This means that for every
second an object falls, its downward
velocity increases by 9.8 m/s.
 Complete Math Focus
on p. 151

AIR RESISTANCE
Drop a feather and a coin. Which hits
the ground first? Why?
Air resistance slows down the
acceleration.
AIR RESISTANCE
Air resistance is also known as fluid
friction.
 Air resistance depends on the size and
shape of an object.
 Air resistance slows down the acceleration
of falling objects.

ACCELERATION
 Acceleration
stops at the terminal
velocity.
 As long as the net force on a falling
object is not zero (0), the object
accelerates downward.
 As the speed of the object increases,
the amount of air resistance also
increases.
ACCELERATION
As an object falls, the upward force of air
resistance continues to increase until it
matches the downward force of gravity
(the net force is zero).
 When this happens, the object stops
accelerating, then falls at a constant
velocity called the terminal velocity.

FREE FALL
 Free
fall only happens if gravity is
the only force acting on an object.
 It can only occur where there is
no air (in a vacuum or in outer
space).
FREE FALL
Sky divers are NOT in free fall because air
resistance is always acting on them.
 Orbiting objects are in free fall.

ORBITS AND ORBITING
An orbit is formed
by combining
forward motion and
free fall.
 Objects in orbit
appear to be
weightless
because they are
in free fall.

ORBITS AND ORBITING

A centripetal force
is needed to keep
objects in circular
motion. Gravity
acts as this
centripetal force.
PROJECTILE MOTION

Projectile motion is
the curved path an
object follows
when thrown or
propelled near the
surface of the
Earth.
PROJECTILE MOTION

Projectile motion has
two components
(parts):
 1.
horizontal
 2. vertical
Gravity only affects the
vertical motion of
projectile motion
See Figure 9 on p. 155
of text.
EXAMPLES OF PROJECTILE
MOTION