Modeling Motion

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Modeling Motion
CPO Physics
Taken from a presentation original by Patsy
Decoaster
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Page 19
Monday 9/13
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Modeling Motion
Practice
KISS, brief notes! Each slide less than 1
minute! Record less than 5 to 7 words per slide!
Write Study questions after class!
Write Summary after class!
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Relative Position
QUESTION How can you tell something has moved?
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Distance from 1st Position
Motion is always relative to a frame of reference.
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Frames of Reference

• The object or point from which movement is
  determined
• Movement is relative to an object that appears
  stationary
• Earth is the most common frame of reference

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Questions

• What is the frame of reference for the sunset?
• What is a frame of reference?
• What is the most common frame of reference?

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Question

• When can you determine how fast you are going in
  a jet plane?

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Unit 1 Mechanics
Chapter 2 Linear Motion

• Motion is Relative
• Speed and Velocity
• Graphs of Motion

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Speed

• Key Question
• What is speed and
• how is it measured?

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Speed
Distance traveled (m)
v d t
Speed (m/sec)
Time taken (sec)
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Calculate speed
Practice problem Guess method on your slate!

• A bird is observed to fly 50 meters in 7.5
  seconds.
• Calculate the speed of the bird in m/sec.

d 50m t 7.5s v dt v 50 m 7.5 s
6.67 m/s
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Calculate distance

• How far do you go if you drive for 2 hours at a
  speed of 100 kilometers per hour?

Practice problem Guess method on your slate!
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Calculate time
Practice problem Guess method on your slate!

• A space shuttle is traveling at a speed of 7,700
  m/sec.
• How far does the shuttle travel in kilometers in
  one hour?

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Units for Speed
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Calculating Speed

• Why the letter v is used for speed...
• We use the letter v to represent speed in a
  formula.
• If this seems confusing, remember that v stands
  for velocity.
• Speed is a single measurement that tells how fast
  you are going, like 100 km/h.
• Velocity means you know both your speed and your
  direction.

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Average speed

• Total distance divided by the total time
• Formula
• Total distance
• total time

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Velocity

• Speed in a given direction
• Represented by a vector.
• Velocities in the same direction combine by
  adding
• Velocities in opposite directions combine by
  subtracting
• Velocities added with vector geometry.

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DisplacementDistance and Direction
Displacement / time Velocity.
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Graphical Data

• To a scientist, a graph is a language that shows
  the relationship between two variables.
• By convention, graphs are drawn a certain way
  just like words are spelled certain ways.

This graph shows the relationship between speed
and distance.
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Graphical Data

• Speed, the dependent variable goes on the y-axis.
• Distance is the independent variable and goes on
  the horizontal or x-axis.

This graph shows the relationship between speed
and distance.
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Using graphical models
If the graph is created from accurate data, the
prediction will also be accurate.
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Recognizing relationships in data

• Cause and effect
• Patterns indicate relationships

Strong relationship between variables
NO relationship between variables
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Recognizing Relationships in Data
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Analyzing Motion with Graphs

• Key Question
• How do you model motion?

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How to make a graph

• Decide what to put on the x and y axes.
• Make a scale by counting boxes to fit your
  largest value (multiples of 1, 2, 5 or 10 are
  best).
• Plot your points.
• Draw a best fit curve.
• Create a title and label
• each axis.

Speed vs. Distance
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Position time graph
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Interpret a position time graph

• The position versus time graph shows a boat
  traveling through a long canal.
• The boat has to stop at locks for changes in
  water level.
• a) How many stops does the boat make?
• b) What is the boats average speed for the whole
  trip?
• c) What is the highest speed the boat reaches?

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Slope

• The slope of a line is the ratio of the rise
  (vertical change) to the run(horizontal change)
  of the line.

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Constant Speed

• On this graph, a constant speed is a straight
  horizontal line.

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Application Slow-motion Photography