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Motion
Motion
Motion
Motion
Motion
In physics…
MOTION means a change in the location of a body
It is the result of applied force
Typically described in terms of velocity,
acceleration, displacement, and time.
Velocity cannot change unless it is acted upon by
a force, as described by Newton's first law.
Momentum is directly related to the object's mass
and velocity, and the total momentum of all
objects in a closed system (one not affected by
external forces) does not change with time, as
described by the law of conservation of momentum.
A body which does not
move is said to be at rest
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Motion is always observed
and measured relative to a
frame of reference
As there is no absolute reference frame, absolute motion
cannot be determined; this is emphasized by the term relative
motion. A body which is motionless relative to a given
reference frame, moves relative to infinitely many other
frames. Thus, everything in the universe is moving.
Measuring Motion
Motion is measured by
distance, using either
standard or metric system
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Standard
Metric
Inches
Centimeters
Yards
Meters
Miles
Kilometers
And now, the metric
system in 30 seconds…
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To convert, move the decimal
For example, if you have 287.4 cm, and want to know
how many decameters that is, move the decimal 3
places to the left = 0.2874 decameters
Calculating Speed
Speed =
Distance (d)
Time (t)
Speed – the distance an object travels in one unit of time
Measured in length per unit time, such as meters per second
(Meters per second is written as m/s or m/sec)
Constant Speed – speed of an object does not change
Average Speed – total distance divided by the total time
Instantaneous speed – object’s speed at a particular
moment in time
Velocity – speed in a given direction
Graphing Speed
When graphing
speed, time is
put on the X-axis,
and distance on
the Y-axis
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Calculate the speed of Student A and
Student B from the graph
Graphing Speed
Student A
Travels 1 meter in
1 second
S = d/t
S = 1 meter/1 second
S = 1 m/sec
Student B
Travels 0.5 meters in
1 second
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S = d/t
S = 0.5 meter/1 second
S = 0.5 m/sec
Acceleration
Acceleration =
Final speed (Sf) – Initial speed (Si)
Time (t)
Change in speed divided by the time it takes to make that change.
Acceleration occurs when an object’s speed
increases or decreases.
The car’s speed is increasing,
acceleration is to the right
(acceleration is the same
direction of the motion)
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Direction of Motion
The car’s speed is decreasing.
Acceleration is now to the left
(acceleration is in the opposite
direction of the car’s motion)
Graphing Acceleration
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When graphing
acceleration, time is put
on the X-axis, and speed
is now on the Y-axis.
Look at this graph.
A = positive acceleration (in the same direction as motion)
B = constant speed
C = negative acceleration (in the opposite direction as
motion)
Momentum
Momentum refers to how hard it is to stop an object.
An object with greater inertia, once in motion, will require
more force to affect its motion.
Which would
be harder to
stop?
To calculate momentum,
multiply the object’s mass by its velocity
P=m●v
Vectors
75 North of West
N
Vector - a quantity that has
75
magnitude and direction.
W
E
Vector
direction
S
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Vector
magnitude
and direction
In the example to the left,
the force of 316 N
represents the magnitude,
being applied in a
direction of 35 North of
East.
(seconds)
Time
Speed
(m/sec)
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190
0
200
0
Make a graph
of acceleration
using the data
to the left
Graphing
When making graphs, remember the
following:
For speed graphs
Time goes on X-axis
Distance goes on Y-axis
For acceleration graphs
Time goes on X-axis
Speed in meters per second
(m/sec) goes on Y-axis
(seconds)
Time
Speed
(m/sec)
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5
20
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What is the independent variable?
What axis does it go on?
(seconds)
Time
Speed
(m/sec)
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How should we divide up the x-axis?
Time (seconds)
(seconds)
Time
Speed
(m/sec)
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What is the dependent variable?
What axis does it go on?
0
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Time (seconds)
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90
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Time
Speed
(m/sec)
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How should we divide up the y-axis?
Speed (m/sec)
(seconds)
0
5
10 15
20
25
30 35
40
45
50
55
60
65
70
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Time (seconds)
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90
95 100 105 110 115 120 125 130
(seconds)
Time
Speed
(m/sec)
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20
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190
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180
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170
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What else is missing?
220
210
Speed (m/sec)
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Time (seconds)
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Time
Acceleration
(seconds)
Speed
(m/sec)
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170
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220
210
Speed (m/sec)
200
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150
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130
120
110
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90
120
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130
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70
140
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10
190
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200
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10 15
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30 35
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Time (seconds)
90
95 100 105 110 115 120 125 130
Review
Speed = distance/time (for example, meters/second or km/hr)
Velocity = speed in a given direction
Acceleration = change in speed / time (units are usually something
like meters/second2
A football player sprinted 40 yards in 5 seconds.
What was its speed?
V = d/t
V = 40 yds / 5 seconds
V = 8 yd/sec
A baseball was thrown 30 meters and it took the ball 2
seconds to cover the distance. What was the ball’s speed?
V = d/t
V = 30 meters / 2 seconds
V = 15 m/sec
While sky diving, Captain Kirk fell 3000 meters in 10 seconds.
What was his speed?
V = d/t
V = 3000 m / 10 s
V = 300 m/s
Trying to get home after work, Jane was able to go 4 miles
in 4 minutes, the next 2 miles took 6 minutes due to traffic.
The final 4 miles took 5 minutes and she was home. What
was her average speed?
Vaverage = Total distance / total time
Vaverage = (4 miles + 2 miles + 4 miles) / (4 mins + 6 mins + 5 mins)
Vaverage = 10 miles / 15 minutes
Vaverage = 0.67 miles / minute
Vaverage = 40 miles/hour
In the final play of the game, the quarterback scrambled 10
yards in 5 seconds, then he ran 10 more yards in 10 seconds,
and then he ran the final 15 yards in 5 seconds into the end
zone for the win! What was his average speed?
Vaverage = Total distance / total time
Vaverage = (10 yards + 10 yards + 15 yards) / (5 secs + 10 secs + 5 secs)
Vaverage = 35 yards / 20 secs
Vaverage = 1.75 yards / sec