Velocity Review
• 1.
What is the difference
between speed and velocity?
• 2. Write down an example of
speed and an example of
velocity.
Even More Practice
• A plane is flying from Atlanta to San
Diego at 520 mph west. It encounters
wind from the jet stream moving at 30
mph east. What is the planes resultant
velocity?
• What about if the plane were headed
east from San Diego to Atlanta instead?
Bellringer
• Give an example of an
object in freefall.
3.3 Acceleration and direction
•
Remember..a change in velocity occurs
whenever there is a change in speed,
direction, or both.
3.3 Acceleration
•
Acceleration is the rate at which
velocity changes. (How quickly an object
changes speed or direction)
3.3 Speed and acceleration
• Speed and
acceleration are
not the same
thing.
• Acceleration is
the change in
speed divided by
the change in
time.
Acceleration Calculations
If you start from a standstill and are
going 5 meters per second at the end of
5 seconds, what is your rate of
acceleration?
Explain why each of the
following is an example of
acceleration….
•
•
•
•
A plane taking off
Stopping at a corner
Jogging on a track
Driving around a
corner
•
•
•
•
Increase in speed
Decrease in speed
Change in direction
Change in direction
3.3 Acceleration and motion graphs
• A speed vs. time
graph is useful for
showing how the
speed of a moving
object changes over
time.
• If the line on the graph
is horizontal, then the
car is moving at a
There is no change in speed
constant speed.
so there is no acceleration.
3.3 Acceleration and motion graphs
• Like velocity,
acceleration can be
positive or negative.
• Positive
acceleration adds
more speed each
second.
Speed is increasing at
the same rate.
3.3 Acceleration and motion graphs
• Negative acceleration
subtracts some speed
each second, so things
get slower.
• People sometimes use
the word deceleration
to describe slowing
down.
Speed is decreasing at
the same rate.
Graphing Acceleration
•
Between which 2
points do you find:
1. Negative
acceleration?
2. Positive
acceleration?
3. Steady speed?
Try this one…
• A coconut falls from the top of a tree
and reaches a velocity of 19.6 m/s when
it hits the ground. It takes 2 seconds to
reach the ground. What is the
coconut’s acceleration?
(remember to include units and direction
in your answer)
Solution
• a = (v2-v1) =
t
What force is causing the coconut to fall
downward?
Solution
• a = (v2-v1) =
t
What force is causing the coconut to fall
downward?
GRAVITY
3.3 Free fall
• An object is in free fall
if it is accelerating due
to the force of gravity
and no other forces are
acting on it.
• Objects in free fall on
Earth accelerate
downward.
3.3 Free fall
• Falling objects increase their speed by 9.8
m/s every second, or 9.8 m/s2
• The letter “g” is used for acceleration due to
gravity.
3.3 Acceleration and direction
•
Acceleration occurs whenever there is a
change in speed, direction, or both.
3.3 Acceleration and direction
•
A car driving around a curve at a
constant speed is accelerating because
its direction is changing.
3.3 Curved motion
• A soccer ball is an
example of a projectile.
• A projectile is an object
that is moving forward
AND is also under the
influence of gravity.
3.3 Curved motion
• Circular motion is
another type of curved
motion.
• An object in circular
motion has a velocity
vector that constantly
changes direction.
Section Review – page 73
• 3, 4, 5
• 7, 8, 9