Comparing Speeds

1
Comparing Speeds

• Investigation 3

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Part 1Walk/Run Race

• How fast can you run?
• How fast can you walk?
• How fast can you walk backwards?
• How fast can you skip?
• Set up an experiment to find out your speeds.
• 10 m distance
• Each person will complete an experiment write up
  and a data sheet on their own speeds.

3
Set up and Expectations

• Whats the most efficient way to set up a 10m
  distance for multiple use?
• How many trials for each?
• Why?
• Set up your personal data table in your journal.
• Work in pairs to finish all your trials.
• Any trials not done will be counted against you
  on your total lab score.

4
Walk and Run Sample Results

• These are the results obtained by one group of
  students. Eddy was the groups walker and Molly
  was the runner.
• Which traveler moved at a greater speed?
• What two pieces of information suggest that Molly
  went faster?
• What does the slope of the line on a speed graph
  tell you about the speed of the moving objects?
• How can you use the graph to determine to average
  speed of the walker and runner?

5
The Challenge

• I want you to plan a race between a runner and a
  walker. The race is not, however, to see which
  contestant can cross the finish line first the
  usual goal of a race. Rather, the goal is for
  both to cross the finish line at the same time.
• Your challenge is to set up a race in which both
  the walker and runner move at their usual speed
  and finish the race at exactly the same time.
• Come up with a plan.

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Solutions?

• The two racers can both position themselves on
  the start /finish line, but the walker starts
  first. This is a time head start.
• The two racers can position themselves at
  different distances from the finish line and
  start moving at the same time. This is a
  position head start.

7
So, How Much?

• So, how much of a head start is needed?
• Figure out how much of a head start is needed in
  your journal. Show all your work.

8
Time Head Start

• How long does it take Eddy to go the 20m?
• How long does it take Molly to go the 20m?
• So when should Molly start?
• 18.1 s 8.0 s 10.1 s
• Molly should start 10.1 s after Eddy starts
  walking

9
Using the Graph

• You can find the same information w/o using
  subtraction. You can find it with parallel lines
  on the graph.
• Find where two graph lines so that it passes
  through the point where Eddy intersects the 20m
  line.
• Use your ruler to edge Mollys run
• Now slide your ruler over until it intersects
  with Eddy at 20m

10
Position Head Start

• We found out to figure head start using time, now
  how do we do it for a position head start?
• How do we know where both start at the same time
  to end at the 20 m mark at the same time?
• How fast can Molly run 20m?
• So how far can Eddy walk in that amount of time?

11

• By running your finger up the graph on the 8s
  line to where it intersects the Eddys graph
  line, we can project over to the y-axis to see
  that Eddy goes about 9m in 8s.
• So, where does Eddy need to start?
• 11m from the start line
• How cool is that?

12
Try It?

• With your partner you will complete WS 27.
• You need to complete three races.
• With both of you finishing at the same exact time
  without fudging.
• We have a 10m course, how can we use that same 10
  m course to complete all three races?
• Use your journal to do your graph work.
• Be sure to write down all your thinking and show
  all your work.

13
Its a Photo Finish!

• Whats a photo finish?
• A photo is snapped just as the horses cross the
  line. Officials study the photo to see which
  horse crossed the finish line first. Such a race
  is said to end in a photo finish.
• Were going to work on the computer on a program
  called Photo Finish.

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Its off to the races

• Choose two contestants to race, calculate their
  speed, and plan a race that will result in a
  photo finish.
• You will have magic graphs to help you determine
  how much of time head start one of the racers
  will need so that the race results in a photo
  finish.
• After you achieve your photo finish with your two
  racers, you will match them in a second race that
  is twice as long as the first race.
• Stage three different races with different sets
  of contestants.
• Each person must complete their own worksheet for
  credit.
• Dont be a mouse hog.

15
Race Tricks on the Computer

• Guidelines on the graph screens can be pulled
  into the action to line things up more
  accurately.
• The graph lines can be dragged to help predict
  head-start times.
• Print out your race results each time to staple
  to your lab sheet.

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Part 2 - Boat Races

• The four boat all went different distances and
  traveled different lengths of time.
• What are two ways you could use to determine
  which one traveled at the fastest speed, which
  was second fastest, and so on?
• Use the speed equation, or
• Make four distance-versus-time graphs on one grid
  and compare the slopes.

17
Graphing Reminders

• Label your x-axis and y-axis
• All boats are starting at (0,0)
• Each boat will have a separate line
• Be sure to label which line is which boat.
• Now, do the extra credit b/c its not. Its
  required!
• Draw a flat line on 100m
• Use your ruler to slide all the data lines to a
  point at which they all reach 100m at the same
  time.
• Write the starting time for each in the table
  provided.

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Still Boating

• Write Boating Questions in your journal and
  underline it. Answer each of the following
  questions, you do not need to answer in complete
  sentences this time!
• Use your worksheet and graph to help you answer
  the questions.

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Boating Questions

• Which boat traveled at the highest speed? How
  fast was it going?
• How can you tell which boat went fastest when you
  look at the graph?
• Which boat(s) traveled the longest distance?
• The shortest distance?
• What does the length of the line tell you about
  speed?

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And more questions

• What was Tornados average speed? Show all your
  math.
• How far would Tornado travel in 5 minutes? How
  did you figure that out? Show all your math.
• What time should each boat start in order for all
  four to finish at the same time at the 100 m mark?

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Boat Challenge

• Mango starts across the boat pond. Forty seconds
  later Whisper starts after Mango.
• How long does it take Whisper to pass Mango?
• How far from the initial starting position will
  the boats be when Whisper passes Mango?
• Use your journal and graph paper to help you out.
• How do you figure this out?

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Part 3 - Iditarod

• The Iditarod is an annual dog-sled race named for
  a small town in central Alaska. Dozens of dog
  teams and mushers meet each spring to see who can
  make it through the difficult course fastest. The
  race has a colorful history and many rules and
  regulations that must be followed by every
  competitor.
• http//www.iditarod.com/

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Iditarod cont

• Susan Butcher was the second woman to win the
  race, and is the only woman to win four times.
  As you will see when you study the details of her
  first winning year, it took her a significant
  amount of time to complete the long race.

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Iditarod Reading

• The image and the short text on the page provide
  information you will need in order to answer the
  questions on the sheet. Work with your group to
  find solutions.
• http//www.iditarod.com/2-9.html

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Tidbits of Info.

• Susan stopped at 24 checkpoints because in even
  years (1986) the race takes the northern route.
  The start (Anchorage) and finish (Nome) are not
  checkpoints.
• All but three of the checkpoint stops were 3
  hours long. 21x3 h 63 h at rest
• One checkpoint stop was 24 hours and two others
  were 8 hours each. 24h 8h 8h 40h at rest.

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Tidbits cont

• The total time mushing on the race course is the
  total time minus the sum of the checkpoint stops
  (at rest).
• Susans average speed while actually traveling on
  the race course is equal to the total distance
  divided by the total times mushing. V d/ t
  1800km/176h 10.2 km/h.

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Iditarod Reading

• Open your books to page 11-16.
• Answer the 4 questions on page 16 using the
  question in your answer.
• Show Time!