Average Speed

1
Average Speed

• Mrs. Martinez
• Sixth Grade

2
Welcoming Work

• Review
• What is Force?
• What is a balanced force? Describe by using
  arrows to draw a diagram.
• What is an unbalanced force? Describe by using
  arrows to draw a diagram.
• Getting your brain gears turning.
• What is a distance-time graph?
• What is Motion?
• What is the connection between Speed, Distance,
  and Time?

3
Forces

• A force is a push or pull that one body exerts on
  another. A force can cause the motion of an
  object to change. There are two types of forces
• Balanced force one in which the net force is
  zero.
• Unbalanced force one in which the net force has
  a numerical value.

4
Forces
Balanced Force Net force 0
- 1 force
1 force
Unbalanced Force Net force -1
1 force
- 2 force
Unbalanced Force Net force 2
1 force
1 force
5
Turn and Talk

• What is motion?

6
What Is Motion?

• Motion is when an object changes place or
  position. To properly describe motion, you need
  to use the following
• Start and end position?
• Movement relative to what?
• How far did it go?
• In what direction did it go?

7
Motion Re-Cap

• When an object changes its position, motion has
  occurred.
• Distance- How far an object has moved.
• Displacement- How far an object has moved in
  relation to its starting point.
• Consider direction
• Example Two runners travel along the same
  straight path in a straight line for 500 meters.
  At the end of the run their distances are the
  same but their displacements are different. How
  can this be so?

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SPEED
Describes how fast an object is moving.
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What Is Speed?

• Speed is the distance an object travels in a
  certain amount of time (relationship of all 3)
• To calculate speed, you use the following
  formula
• Speed (s) Distance(d)
• Time (t)

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Speed- Distance an object travels per unit of
time

• Relationships between speed, distance, and time
• Speed Distance/ Time d/ t
• Constant Speed- speed does not change over time
• Average Speed- speed of motion when speed is
  changing
• Avg Speed Total Distance/ Total Time
• Instantaneous Speed- speed at any given moment in
  time (speedometer)

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The 3 formulas for Speed, Time Distance Using
your W/B write them down without using your
notes.
Solving for Speed
Solving for Time
Solving for Distance
Remember them from this triangle
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Dont Remember huh? Well lets refresh that
memory!

• http//www.youtube.com/watch?v9x7hP5LM1UE

13
Turn and Talk What is the Relationship between
speed, distance and time?

• Speed is the distance an object travels in a
  certain amount of time

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Average Speed
Total distance
Average Speed
Total time
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WB Time!

• Lets check out your knowledge! Without using
  your notes answer
• What is the formula for finding speed?
• What is the formula for finding time, using
  distance and speed?
• What is the formula for finding distance using
  speed and time?

16
Try this

• Mrs. Martinez walks home from her sisters house
  everyday. It takes her 4 minutes and her house is
  240 meters away.What is her average speed?
• 240 meters/ 4 minutes
• 60 meters per minute.

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Example Question 1

• Jane drives at an average speed of 45 mph on a
  journey of 135 miles.How long does the journey
  take?
• To find a time, we need to divide distance by
  speed.
• 135 miles 45 mph 3 hours

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Example Question 2

• Chris cycles at an average speed of 8 mph.If he
  cycles for 6½ hours, how far does he travel?
• To find a distance, we need to multiply speed by
  time.
• 8 mph 6.5 hours 52 miles

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Example Question 3

• Nikki has to travel a total of 351 miles. She
  travels the first 216 miles in 4 hours.(a) What
  is her average speed for the first part of the
  journey?
• To find average speed, we need to divide
  distance by time.
• 216 miles 4 hours 54 mph

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• Her average speed is the same for the whole of
  her journey.
• (b) How long does the whole journey take?
• To find time, we need to divide distance by
  speed.
• 351 miles 54 mph 6.5 hours

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Reminder How to change minutes into a decimal
15 mins 025 hour So 3 hours 15 mins 325
hours
30 mins 05 hour So 7 hours 30 mins 75
hours
45 mins 075 hour So 2 hours 45 mins 275
hours
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First work it out on your paper then show me on
your WB. A windsurfer travelled 28 km in 1 hour
45 mins. Calculate his speed.
Speed
1 hour 45 mins
16 km/h
Answer His speed was 16 km / hour
23
A salesman travelled at an average speed of 50
km/h for 2 hours 30 mins. How far did he travel?
Distance
Speed x Time
2 hour 30 mins
50 x 25
125 km
Answer He travelled 125 km
24
A train travelled 555 miles at an average speed
of 60 mph. How long did the journey take?
Time
925 hours
9 hours 15 mins
Answer It took 9 hours 15 minutes
25
Speed Problem

• Suppose you ran 2 km in 10 min. What is your
  speed?
• S 2 km 0.2 km/min
• 10 min

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Ways To Calculate Speed

• Constant speed is when you are traveling at the
  same rate of speed, such as 55 mph constantly on
  a highway.
• Average speed is taking the total distance
  traveled, and dividing by the total time it
  takes. Used for calculations that involve
  changing speed.
• Instantaneous speed is the speed at any one given
  point in time.

27
Sooo What is the formula for speed?

• http//www.youtube.com/watch?featureendscreenvK
  _kzgW_OYX0NR1

28
Practice Question 1

• Jim travels 45 miles at 15 mph.How long does it
  take him?

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• 45 miles/15 mph
• 3 hrs.

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Practice Question 2

• Jemimah walks at 4 mph for 2½ hours.How far
  does she walk?
• She walked 10 miles.
• 4 mph x 2.5 hrs 10 miles

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Practice Question 3

• Jenny drives at a constant speed. In the first
  three hours she travels 81 miles.How far will
  she have travelled after 5 hours?
• She will travel 135 miles
• 27 mph for 5 hrs 135 miles

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Graphing Average Speed

• Using a Distance-Time Graph

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Graphing Motion

• Graph distance on the y-axis and time on the
  x-axis

• Slope rise distance speed
• run time

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Graphing Speed

• Speed is usually graphed using a line graph, and
  it depicts the distance and time.
• Time is the independent variable, and thus is
  ALWAYS on the x-axis.
• Distance is the dependent variable, and is ALWAYS
  on the y-axis.

35
Average Speed
What is the AVERAGE speed of the bass boat
depicted in the graph?
Average Speed 125 meters 15.6 m/s
8 seconds
36
Instantaneous Speed
What is the instantaneous speed of the bass boat
at t7 seconds?
Instantaneous Speed 85 meters 12.1 m/s
7 seconds
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Speed Graphs

• In what time period is the bass boat speeding up?
  
• In what time period is the bass boat slowing
  down?
• When is the speed NOT changing?

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Distance - Time Graph

• If something is not moving, a horizontal line is
  drawn.
• If something starts out slow and then speeds up,
  its change in speed can look like this.

39
Learning Checkpoint

• This graph shows several stages of motion
• Stage 1 100 m in 10 s
• Stage 2 50 m in 10 s
• Stage 3 150 m in 20 s
• Calculate the speed as indicated by each of the
  colors.
• Calculate the average speed.
• What is the total distance?
• What is the displacement?

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Solution
Stage 1 S d/ t 100 m/ 10 s 10 m/s Stage 2
S d/t 50 m/ 10 s 5 m/s Stage 3 S d/t 150 m/
20 s 7.5 m/s Avg Speed Tot d/ Tot t 300 m/ 40
s 7.5 m/s Distance 300 meters Displacement 0
meters
41
3) At a daily basis, you rotate between classes.
Draw a distance vs time graph illustrating the
distance you travel during class rotations here
at school
42
Video Recap

• http//www.youtube.com/watch?vSpz8WfmREDMNR1fe
  aturefvwp

43
Average Speed Recap

• http//www.youtube.com/watch?vWxCgVNqfub8

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Velocity
The speed of an object in a certain direction.
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Velocity

• Velocity is the speed of an object, but the
  direction is also included. It is calculated the
  same as speed, but you must include a direction
  in your answer.
• Example the bass boat was moving 12 mph toward
  the north.

46
d
Velocity
V
t
speed of an object in a certain direction.
V velocity (meters/second) d distance
(meters) t time (seconds)
47
Velocity
speed of an object in a certain direction.
0
seconds
3
1
2
48
Velocity

• The speed and direction of an objects motion.
• 88 km / hr southwest

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Speed? Velocity?
B
Total time 4 seconds
20 meters
12 meters
16 meters
A
50
Acceleration

• Acceleration is the rate of change of velocity.
  A change in velocity can be either a change in
  speed, or direction, or both.
• Deceleration is when acceleration has a negative
  value.

51
Acceleration

• The formula for calculating acceleration is
• Acceleration (a) final velocity (vf) initial
  velocity (vi)
• time
  (sec)
• The unit for velocity, in this case, is
• m/s/s OR m/s2

52
Acceleration Math Problem

• A jet starts at rest at the end of a runway and
  reaches a speed of 80 m/s in 20 s. What is its
  acceleration?
• a 80 m/s - 0 m/s 4 m/s2
• 20 s

53
Acceleration Math Problem

• A skateboarder is moving in a straight line at a
  speed of 3 m/s and comes to a stop in 2 sec.
  What is his acceleration?
• a 0 m/s - 3 m/s -1.5 m/s2
• 2 m/s

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Inertia

• Inertia is the tendency of an object to resist
  any change in motion. Put in another way, if an
  object is moving, it will keep moving until an
  outside force acts on it.
• Inertia is related to mass the greater the mass
  of an object, the greater its inertia.

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Newtons 1st Law of Motion

• Newtons 1st Law is also known as the law of
  inertia. It says
• An object in motion will stay in motion, and an
  object at rest will stay at rest, unless acted
  upon by an outside force.
• Example if you are approaching a fence on a
  running horse, and the horse suddenly stops, you
  will keep going forward over the horses head
  unless you are wearing a seatbelt! (I dont care
  who you are thats funny!)

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Inertia

• What does a seat belt do for us,
• in terms of inertia?
• -it helps us OVERCOME inertia!

57
http//www.cimt.plymouth.ac.uk/projects/mepres/boo
k8/bk8i18/bk8_18i2.htm http//baldragon.ea.dunde
ecity.sch.uk/Departments/Physics/Movementint1/Aver
agespeedweb.htm