Transcript Section 3.3 - CPO Science

Motion and Force
Chapter Three: Motion
• 3.1 Position and Velocity
• 3.2 Graphs of Motion
• 3.3 Acceleration
3.3 Acceleration
•
Acceleration is the rate at which
velocity (speed) changes.
If your speed increases by 1 m/s each second, then
your acceleration is 1 m/s per second.
What is the acceleration for the steeper hill?
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.
3.3 Speed and acceleration
• An acceleration in
m/s/s is often written
as m/s2 (meters per
second squared).
• It is better to think
about acceleration in
units of speed change
per second (that is,
meters per second per
second).
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.
3.3 Acceleration and motion graphs
•
•
The position vs. time graph shows acceleration
more clearly.
This graph is a curve when there is
acceleration.
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
•
Individual vectors can be drawn to scale
to calculate the change in direction.
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
moving under the
influence of only gravity.
• The path of the ball
makes a bowl-shaped
curve called a parabola.
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.
Technology Connection
Moments in Motion
• Some things move too
quickly for us to see what
is really happening.
• Special photography can
capture fast action in still
images that reveal a
whole new world to our
eyes.
Activity
How Fast are You?
• Speed is how fast something
moves in relation to a
reference point without regard
to the direction.
• In this activity you and a
partner will each calculate your
average speed in different
units.