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