Transcript Speed vs. Velocity Reviewing Key Concepts pg. 347 1a. What is speed? Speed is distance traveled per unit time. b.

Speed vs. Velocity
Reviewing Key Concepts pg. 347
1a. What is speed?
Speed is distance traveled per unit time.
b. What is the average speed of a car that
travels 160 km in 2 hours?
80 km/h
c. If you walked at an average speed of
1.2 m/s, how long would it take to cross
a road that is 16-m wide? Note: units
16 m
1.2 m/s
=
13 1/3 s
m
m
s
∙
m s
= 1 m
2a. What is velocity?
Velocity is speed in a given direction.
b.Describe the two ways in which velocity
can change.
Velocity can change in speed or direction
or both.
c. Your car’s speedometer reads a constant
35 mi/hr. Can you say your velocity is
constant? Explain.
Probably not. The question does not give
information about change (or no change)
in direction. Velocity involves both
speed and direction.
3a. What does the slope of a distance-
versus-time graph show you about the
motion of an object?
The slope of a distance-versus-time
graph shows you the speed of the
moving object.
b. The rise of a line on a distance-versus-
time graph is 600 m and run is 3
minutes. What is the slope of the line?
The slope is 200 m/min.
Activity 75
Title: Interpreting Motion
Graphs
When you measured the speed of a cart
rolling down a track, do you think the carts
were going the same speed the whole time?
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The cart started at rest (0 cm/s)
It then sped up to its top speed down the
ramp
It eventually slowed down until it stopped
came to rest (0 cm/s)
You found the AVERAGE SPEED
INSTANTANEOUS SPEED is the speed at any
given moment in time (speedometer).
In this activity...
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You will analyze graphs of distance versus
time that show motion over a whole trip.
The motion may be different throughout
the trip.
Notice on pg. E-12, the road to school is a
straight road and does not require any
turning. This activity focuses on linear
motion only.
Read E-12
Problem: How can you use a graph to
describe motion?
Hypothesis: If you _____________, then
you ____________________.
Distance (mi)
What do you know about reading a
motion graph?
x-axis is time
Y-axis is
distance
Time (hr)
Procedure
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Trip Slips – figure out where they go on the
graphs!
You will be exploring how the slope on the
graph relates to speed. You will also
analyze graphs of distance versus time
that show motion over a whole trip, as
opposed to determining one average
speed over a trip
What do the changes in the
graph’s slopes on a distanceversus-time graph mean?
Background information:
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A straight line indicates a constant speed.
A positive (upward) slope means the car is
moving away from the reference point
(home), or positive velocity
A zero slope (horizontal line) is a stopped
car.
A negative (downward) slope is a car
moving back toward the reference point
(home), or negative velocity.
Background cont.:
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A steeper slope indicates a faster speed.
A curved line of changing slope indicates
linear acceleration, or change in speed.
The rate of curvature defines the amount of
acceleration.
Slope
Slope =
the change in y (∆y)
the change in x (∆x)
the change in the distance (∆d)
=
the time interval (∆t)
Procedure step #5

Put your explanation of each persons trip on the
back of your template or on separate paper
Data/observation:
Explanations:
Teasha’s Trip:
D- The slope of the line is 3 mi/6 min or 0.5 mi/min, which
shows the car took 6 minutes to travel 3 miles.
Josh’s Trip:
Discussion
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Are Teasha’s and Josh’s graphs realistic?
Do cars usually change speed
instantaneously?
What would be a more realistic way to
draw the graphs?
Distance
Distance
Time
Not Realistic
Time
Realistic
Analysis Question #5
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An object accelerates if it has a change in
speed or direction.
A distance vs. time graph with a constant
slope shows that the speed is constant.
If the slope is increasing, the speed is
increasing and the car is accelerating.
Distance
Distance
Time
Time
Acceleration:
Deceleration:
slope is increasing
slope is decreasing
Graphing Speed:
Distance vs. Time Graphs
200
1600
Denver
Distance (Km)
1400
1200
1000
800
600
400
200
0 Phoenix
2
3
4
5
Time (hr)
6
7
Average speed
• Speed is usually NOT CONSTANT
– Ex. Cars stop and go regularly
– Runners go slower uphill than downhill
• Average speed = total distance
traveled/total time it took.
Calculating Average Speed
• It took me 1 hour to go 40 km on the
highway. Then it took me 2 more hours to
go 20 km using the streets.
• Total Distance:
40 km + 20 km = 60 km
• Total Time:
1 h + 2 h = 3 hr
• Ave. Speed:
total d/total t = 60 km/3 h = 20 km/h
Question
• I ran 1000 m in 3 minutes. Then ran
another 1000 m uphill in 7 minutes.
What is my average speed?
A) 100
m/minm + 1000 m = 2000 m
Total–Dist.
= 1000
– B) 2000 m/min
Total Time = 3 min + 7 min = 10 min
– C) 10 m/min
– D) 200
m/mindist/total time =
Ave speed
= total
– E) 20 m/min
2000m/10 min = 200 m/min = D
Velocity
• Velocity – the SPEED and
DIRECTION of an object.
– Example:
• An airplane moving North at 500 mph
• A missile moving towards you at 200 m/s
Graphing Speed:
Distance vs. Time Graphs
Speed = Slope = Rise/
Rise
Graphing Speed:
Distance vs. Time Graphs
Speed = Slope = Rise/
Rise=?
600 km
3h
Graphing Speed:
Distance vs. Time Graphs
Speed = Slope = Rise/
Rise=?
600 km
3 hr
Rise/
Distance (km)
Different Slopes
8
7
6
5
4
3
2
1
0
Slope = Rise/Run
= 1 km/1 hr
= 1 km/hr
Slope = Rise/Run
= 0 km/1 hr
= 0 km/hr
Rise = 2 km
Rise = 0 km
Run = 1 hr
Run = 1 hr
Slope = Rise/Run
= 2 km/1 hr
= 2 km/hr
Rise = 1 km
Run = 1 hr
1
2
3
4
Time (hr)
5
6
7
Question
Below=isTotal
a distance
vs. timetime
graph
of km/6
my hr
Average Speed
distance/Total
= 12
= 2akm/hr
position during
race. What was my
AVERAGE speed for the entire race?
14
Distance (km)
12
10
8
Rise = 12 km
6
4
2
0
0
1
2
3
Time
Run
= (hr)
6 hr
4
5
6
Question
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Below is a distance vs. time graph for 3
runners. Who is the fastest?
Leroy is the fastest. He completed the race in 3 hours
Acceleration
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Acceleration = speeding up?
Acceleration – the rate at which
velocity changes
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Can be an:
Increase in speed
 Decrease in speed
 Change in direction
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Types of acceleration
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Increasing speed
 Example: Car speeds up at green
light
Decreasing speed
 Example: Car slows down at stop light
screeeeech
Changing Direction
 Example: Car takes turn (can be at
constant speed)
Question
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How can a car be accelerating if its
speed is a constant 65 km/h?
If it is changing directions it is
accelerating
Calculating Speed Worksheet
4 m/s
48
Distance (m)
40
32
24
16
8
0
1
2
3
4
5
6
7
8
Time (s)
9
10 11 12 13 14