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Modeling Motion
CPO Physics
Taken from a presentation original by Patsy DecoasterTaken from a presentation original by Patsy Decoaster
20 Practice
Monday 9/13
Page 19
19Modeling Motion
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!
Relative PositionQUESTION: How can you tell something has moved?
Distance from 1st PositionMotion is always relative to a frame of reference.
Frames of ReferenceThe 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
Questions
What is the frame of reference for the sunset?
What is a frame of reference?
What is the most common frame of reference?
Question
When can you determine how fast you are going in a jet plane?
Unit 1: Mechanics
Motion is Relative
Speed and Velocity
Graphs of Motion
Chapter 2: Linear Motion
SpeedKey Question:
What is speed and
how is it measured?
Speed
v = d t
Distance traveled (m)
Time taken (sec)
Speed (m/sec)
Calculate speed
A bird is observed to fly 50 meters in 7.5 seconds.
Calculate the speed of the bird in m/sec.
Practice problem: Guess
method on your slate!
d= 50m t = 7.5s v = d÷t v = 50 m ÷ 7.5 s = 6.67 m/s
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!
Calculate time A space shuttle is traveling
at a speed of 7,700 m/sec. How far does the shuttle
travel in kilometers in one hour?
Practice problem: Guess method on your slate!
Units for Speed
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.
Average speed
Total distance divided by the total time
Formula: Total distance total time
Velocity
Speed in a given directionRepresented by a vector.Velocities in the same direction combine by adding
Velocities in opposite directions combine by subtracting
Velocities added with vector geometry.
DisplacementDistance and Direction
Displacement / time = Velocity.
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.
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.
Using graphical models
If the graph is created from accurate data, the prediction will also be accurate.
Recognizing relationships in data Cause and effect Patterns indicate relationships
Strong relationship between variables
NO relationship between variables
Recognizing Relationships in Data
Analyzing Motion with Graphs
Key Question:
How do you model motion?
How to make a graph
1. Decide what to put on the x and y axes.
2. Make a scale by counting boxes to fit your largest value (multiples of 1, 2, 5 or 10 are best).
3. Plot your points.4. Draw a best fit curve.5. Create a title and label
each axis.
Speed vs. Distance
Position time graph
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 boat’s
average speed for the whole trip?
— c) What is the highest speed the boat reaches?
Slope The slope of a line is the ratio of the “rise” (vertical
change) to the “run”(horizontal change) of the line.
Constant Speed
On this graph, a constant speed is a straight horizontal line.
Application: Slow-motion Photography
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