Post on 07-Apr-2018
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The term uniform motion describes an object that moves at a constant
rate in the same direction.
True uniform motion is nearly impossible to maintain in real life
situations.
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5.0 m
t = 1.2 s
The car moved a distance of 5.0 m in a time of 1.2 s. It did not exhibit
uniform motion because it sped up and slowed down.
The average speed of the car is defined as a change in distance during a
time interval.
avgdvt
=
vavg = average speed
(m/s)d = distance travelled
(m)t = time elapsed (s)
The is the greek letterdelta and means change in.
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Practice Problems p.
128
1) A huge ocean wave, or tsunami, travels a distance of 4.0 106 m
in 3.6 104 s. Calculate the average speed of the tsunami.
1.1 102
m/s
2) A Concorde airplane could fly at an average speed of 694 m/s.
Calculate how long it would have taken the Concorde to fly around
the world, which is approximately 4.00 107 m.5.76 104
s
3) An electric train is travelling at an average speed of 6.9 m/s for 4.0 s.
Calculate the distance travelled by the train.
28 m
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0
10
20
30
40
50
0.0 2.0 4.0 6.0 8.0 10.0
Distance vs Time
Distance(m)
Time (s)
Time
t (s)
Distance fromFirst Marker
d (m)
0.0 0
2.0 10
4.0 20
6.0 30
8.0 40
10.0 50
A motorboat is travelling at a constant speed. A person on the shore is
recording the distance the boat travels away from the first marker buoy
every 2.0 s.
text p.129
A distance vs time graph can be plotted to
analyze the motion of the boat.
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0
10
20
30
40
50
0.0 2.0 4.0 6.0 8.0 10.0
Distance vs Time
Distanc
e(m)
Time (s)
slop
e
rise=
run
y=
x
change in
distance
change
in time
average speed=
distance
time
avg
dv
t
=
The slope of a line on a distance-time graph
is equal to the average speed of the object.
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0
10
20
30
40
50
0.0 2.0 4.0 6.0 8.0 10.0
Distance vs Time
Distanc
e(m)
Time (s)
(0,0) (6.0,30)
( )
( )2 1
2 1
y yslope
x x
=
( )
( )
30 0
6.0 0
m
s
=
= 5.0
m/s
So, the boat is moving at a constant rate of
5.0 m/s.
Dont forget to
round to the right
number of sig
digs, baby!
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Distance vs
Time
Distan
ce
(km)
Time
(h)
12
3
The graph shows the motion
of three different cars.
text p.130
Car 1 is travelling at a constant speed, faster than car 2 (slope is
steeper).Car 2 is travelling at a constant speed, slower than car 1 (slope is
not as steep).
All three cars have a constant
speed, because the slope of
their line does not change.
Car 3 is stopped. The slope is zero, therefore the speed is zero.
The distance does not change as time passes.
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read pages 126 130
Practice Problem 4, p.130 (use graph paper)
Extra problems worksheet 1 7
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Time WhenBoat Passes
Marker
t (s)
Speed of the Boatas it Passes Each
Marker
v (m/s)
0.0 5.00
2.0 5.00
4.0 5.00
6.0 5.00
8.0 5.00
10.0 5.00
text p.131 0.00
1.00
2.00
3.00
4.00
5.00
6.00
0.0 2.0 4.0 6.0 8.0 10.0
Speed vs Time
Speed(m
/s)
Time (s)
The boat is exhibiting uniformmotion, so that means the speed does
not change.
A horizontal line has a slope of
zero, and that means that the
speed stays constant as time
passes.
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The slope of a line on a speed-time graph indicates
that an object is either speeding up or slowing down.
Speed vs
Time
Speed
(m/s
)
Time
(s)
A
B
text p.131
Object A is increasing its speed (positiveslope).
Object B is decreasing its speed
(negative slope).
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The area under the line of a speed-time graph
determines the distance the object travels.
Speed vsTime
Speed
(m/s)
Time
(s)
5.0
1
0
A boat is travelling at a rate of 10 m/s
for 5.0 s.
The area under the line forms a
rectangle.area = length x
width( )
m10 5.0 s
s
=
= 50
m
The boat travels a distance of
50 m.
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read pages 130 133
Practice Problem 5, p.133
B1.1 Check and Reflect
page 135 #s 1 13