Chapter 11 Section 3
ž  Velocity
changes frequently throughout our
physical world.
ž  Describing changes in velocity is a necessary
part in describing motion.
ž  Acceleration-
the rate at which velocity
changes.
ž  Remember that velocity is a combination of
speed and direction.
ž  Acceleration can be described as changes in
speed, changes in direction, or changes in
both.
ž  Acceleration is a vector!!
ž  Acceleration
applies to any change in an
object’s velocity.
ž  It results from increases or decreases in
speed.
ž  Deceleration is an acceleration that slows an
object’s speed.
ž  An
example of acceleration due to change in
speed is a free fall.
ž  Free fall- the movement of an object
towards Earth solely because of gravity.
ž  Unit for acceleration:
m/s 2
ž  Objects fall towards Earth at an acceleration
of 9.8 m/s 2
ž  Example:
Riding your bike around a curve.
ž  Like
riding in a roller coaster- your
acceleration is constantly changing because
of the change of speed and direction of the
cars of the roller coaster.
ž  A
steady change in velocity
ž  You
calculate acceleration for straight-line
motion by dividing the change in velocity by
the total time.
Acceleration =
Change in velocity
Total Time
a = (vf - vi)
t
a= acceleration
vi= initial velocity
vf= final velocity
t= time
* units are in m/s 2
ž A
car traveling 10 m/s starts to
decelerate. It comes to a complete stop
in 20 seconds. What is its acceleration?
ž  An
airplane travels down a runway for 4 seconds
with an acceleration of 9 m/s/s. What is its
change in velocity?
ž  A
ball rolls down a ramp. The ball starts from
rest and after 2 seconds is moving 6 m/s. What
is the acceleration of the ball?