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MOTION
Chapter 9
SECTION 9-1
Describing & Measuring Motion
Recognizing Motion
An object is in motion when
its distance from another
object is changing.
Frame of Reference
- the background
or object used for
comparison to tell
if an object is in
motion.
The most
common frame of
reference is the
earth.
This is
Fred
Astaire - a
famous
actor &
dancer.
Where is
he
dancing in
this
movie?
How can
you tell?
Reference point - an object is in
motion if it changes position
relative to its reference point.
Describing Distance
To describe motion, you need
units of measurement.
In the metric system,
these are meters.
Speed
The distance an object
travels in a certain amount of
time.
Constant Speed
Speed
that does
not
change
during
the
motion of
an
object.
Average Speed
- when there
is a change
in the speed
of an object.
Total
distance
divided by
total time =
average
sped.
Velocity
- speed in
a given
direction
(When
both
speed &
direction
are
known.)
Graphing Motion
You can show motion as a line
graph.
- plot distance against time.
X axis = time (horizontal)
y axis = distance (vertical)
(x,y) = location of an object at a
particular time.
Slope of a Line
Slope = steepness, or slant of a
line
- tells you how fast one
variable changes in relation to
the other variable
- the faster the motion
steeper the slope
Calculating Slope
The slope of a line is its rise
divided by its run.
(Choose two points on the line.)
The rise is the vertical difference
between the two points.
The run is the horizontal
difference between the two
points.
The slope is 2 m/s - which
means the that the speed of
the moving object is 2 meters
every 1 second.
- this is a constant slope
y =2x
represents the line
containing the 2 variables.
X = time
y = distance - so each second
the object moves 2 meters
If the speed of the object were 5m/s
then the equation of the line would
be y = 5x
Section 9-2 Slow Motion on
Planet Earth
Some motion is very slow.
The plates that cover the
earth’s surface move maybe 5
cm a year.
Earth’s Tectonic Plates
The movement
of earth’s
crustal plates
causes
earthquakes,
volcanoes,
mountain
building.
Section 9-3 Acceleration
Acceleration is the rate at
which velocity changes.
- refers to:
- increasing speed
- decreasing speed
- changing direction
Increasing Speed
Any time the speed of an
object increases, the
object experiences
acceleration.
Decreasing Speed
When an object’s motion
slows down.
- deceleration or negative
acceleration
Changing Direction
Remember: Velocity involves
both speed & direction.
-So acceleration occurs even
if the speed stays the same
rate BUT the direction of
motion changes.
-ex. A car turning a corner or an
object moving in a circular path.
Circular Motion
Orbits of
planets,
satellites,
space craft,
etc. are
circular
motions.
Circular Motion
So if you
are
moving
at a
constant
speed
on this
ride, you
are still
accelerating
because
-???
Circular Motion
Because
your
direction
is
changing.
Acceleration
To determine acceleration,
you must calculate the
change in velocity during
each unit of time.
Acceleration
Measured in units of:
distance/time/time
- km/s/s or km/s2
- m/s/s or m/s2
Change of speed over time ACCELERATION
Graphing Acceleration
Shows a
change in
speed over
time.
Graphing Acceleration
Constant Speed
- a linear relationship
Acceleration
- a nonlinear
relationship
Graphing Acceleration
Linear relationship - a straight
line graph shows speed is
constant
Nonlinear relationship -a graph
that shows distance versus
time (a curved line)
-as speed increases the graph curves
upward.
THE END