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Analysis of Motion An Introductory Tutorial using VideoPoint in the WINDOWS platform. By David G. Iadevaia, Ph.D. June 2000 TYC Physics Workshops for the 21st Century A Project of Joliet College, Lee College and the National Science Foundation. Preface.

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analysis of motion an introductory tutorial using videopoint in the windows platform

Analysis of MotionAn Introductory Tutorial using VideoPoint in the WINDOWS platform

By

David G. Iadevaia, Ph.D.

June 2000

TYC Physics Workshops for the 21st Century

A Project of Joliet College, Lee College and the National Science Foundation

slide3

The purpose of this tutorial is help students start using the Videopoint program to collect and

analyze data.

It was designed for a student who has never used the Videopoint program.

By following the step by step format the student will be able to:

import a video clip and collect a number of data points from the clip.

produce a graph of the data.

fit a curve to the data (model).

describe the motion from an equation generated by the curve fit.

Specific examples were used to analyze an object with a constant velocity and a constant

acceleration.

The tutorial also contains information on how to edit a video clip using QuickTime Pro.

A separate folder is included with several original video clips which can be used for analysis.

slide4

A Very Brief Review of

Motion According to

Galileo

slide5

Aristotle’s ideas about motion did not satisfy Galileo’s experimental results.

In order to understand and to predict the motion of an object, Galileo abandoned Aristotle’s point of view.

Galileo invented the concept of inertia. That is, an object will continue to do whatever it is currently doing.

slide6

If the object is moving it will continue to do so.

If the object is at rest it will remain at rest.

Galileo’s experiments helped him understand the concept of inertia.

His experiments helped him formulate his ideas about two important concepts dealing with moving objects.

slide7

The concepts are velocity and acceleration.

In order to understand these concepts we must understand what it means when an object moves.

We will say a change of location of an object defines motion. See the object below

New Position

slide8

You notice that the object’s position constantly changed as time went by.

This is proof that motion has occurred.

That which the moving object has is called velocity.

Watch again.

New Position

slide9

If you could mark distance intervals and measure the time it takes for the object to move through the intervals you would then measure its velocity.

Equal Time Intervals

slide10

If the object moves through a distance in the same time interval for each distance interval then the object has a constant velocity.

If we could mark the location of the object in distance and time from a reference then we could easily measure how it moved. Click the mouse to mark the location of the object after each time interval. The object below has a constant velocity.

Equal Time Intervals

Origin or

Reference

slide11

If the object moves through larger distances in the same time for each distance then the object has an acceleration.

If we could mark the location of the object in distance and time from a reference then we could easily measure how it moved. Click the mouse to mark the location of the object after each time interval.

The object below has an acceleration.

Equal Time Intervals

Origin or

Reference

slide13

If there was a method of marking the actual video you just viewed it would be possible to take measurements and calculate the velocity of the rolling ball using a computer.

There is such a method and it utilizes a powerful video analysis program called Videopoint.

We will now use the short video clip and analyze it using Videopoint.

slide14

The following sequence will take you through the steps needed to analyze a video clip using Videopoint.

1. Starting the Program

2. Importing a Movie Clip

3. Playing a Movie

4. Collecting data points

5. Scaling the Frame

6. Analyzing the Data

slide15

1. Starting the program

The Videopoint program is already loaded in the computer.

Click the Videopoint icon .

slide18

2. Importing a Movie Clip

The clip can be previewed here

Play the clip

using this

control bar

Select the clip you would like to to import into VideoPoint from the directory containing the clips

slide19

Input the number of objects you will study…in this case

1

The movie clip will open and be displayed like this

slide20

Main Window

Movie Area

Coordinate

system window

Toolbar

Table Window

slide21

3. Play a Movie Clip

This is the movie control bar..use it to

play the movie or advance it frame by

frame

slide22

Click here and the movie plays

The object will begin to move

slide24

Be sure to have this icon selected before you attempt to take data

The cursor is moved over the object and the mouse button is clicked

This saves a data point with location and time as the coordinates

slide29

Trails Box

You can see the data points on the movie area if you select the trails box

slide30

5. Scaling the Frame

Click on this icon

Insert 1 here and Meter here to set the scale of 1 meter

It is useful to scale the frames…that is to select an object of known length

so the the program “knows” how big a distance interval is

slide35

Graphing the Data

Graph icon

We can now graph the data select the graph icon from the toolbar

slide36

Leave the Vertical Axis as seen

Leave the Horizontal Axis as time

Position

Select position from the pull down menu

slide38

Analyzing the Data

Select this icon

Select linear since you estimate a linear function constant velocity

Now you can have the program fit a curve to the plot

slide39

Equation

Curve

A best fit curve is drawn through the points and an equation is displayed

slide40

Notice the time interval for 15 frames per second is 0.067 seconds

Each frame advances by that amount

Here is the data table for the data collected notice that time went ahead but nothing was recorded

it wasn’t until the 43 frame that displacement data was collected

slide45

By displaying the trails you can easily see that the distance the object travels increases

for a fixed time interval……this is proof that the object is accelerating

slide46

Select the type of curve…in this case

a polynomial

It is easily seen that this is not a straight line but a curved line

slide47

The formula

describing the

curve is seen

here

The curve which fits the data describes a parabola

slide48

Several More Advanced

Techniques

Changing the Origin

Editing a Video Clip

slide50

The origin of the movie is a fixed point in each frame.

That fixed point is the reference for the

coordinate system.

The origin by default is found at the bottom left of the frame.

It remains there for each frame of the clip.

slide51

Here is the (0,0) point, the origin

for each frame in the clip.

Each (X,Y) pair is determined

from this point

slide52

For controlled videos the origin will be the same from frame to frame.

But suppose the origin moves because the camera was moved as in panning to keep the object in the field of view.

You will have to move the origin in each frame to an object which is seen in each frame.

slide53

Selecting a New Origin

Here is the new origin

Notice that it

is never in the

same place

because

the camera is panning

Click on the image to view it

slide54

You must step through each frame one at a time

in order to mark the same point in each frame as

the origin.

To do that you must open the clip as before and

just like you marked the moving object’s position

you now mark the origin position in each frame.

This ensures that the origin is always located by

the program and the program always has a point

of reference.

slide61

Here is an example of a clip which will need to be edited

Click on the image above to see the clip

slide63

Select FILE from the pull down option and select OPEN MOVIE

Using this program you can open an AVI file

slide66

This shaded area represents the front piece of the current video clip you will remove

Now drag this piece to the set point of the beginning frame

slide70

Now drag the controls to the back end of the frame marker

…first the forward one than the back one

the shadow are represents what will be cut

slide72

Notice the last frame is in the window and the control marker is all the way to the end

of the control bar indicating the edit is now done

slide74

Then select

save to save the

edited video clip

Save the file as a MOV file for direct input

to the Videopoint program

Give the new file a name

slide75

Final edited video clip

Click on the image to view it

slide77

Making a video clip is straight forward.

You can use any video camera to do this.

However, the following points should be considered in producing a clip suitable for analysis using the VideoPoint program:

Use a tripod Level the camera

slide78

For the most accurate results the video camera should be perpendicular to the moving object.

Click on image to view

slide79

The object should move across the video camera’s field of view (FOV) without the camera having to pan as the object moves.

Click on image to view

slide80

Keep the FOV constant during the taping….

DO NOT zoom in on the moving object.

Click on image to view

slide81

A reference object of know length should be included in the FOV. This object could be a ruler or a know dimension in the FOV such as the width between fence posts or the size of the moving object.

Click on image to view

slide82

Remember in a laboratory setting you can control many variables which would affect the accuracy of the final video clip you will use for analysis.

The technique used in producing your own controlled video clip in the laboratory will be the basis on which you plan your recording of an event in the field.

slide83

1. Maintain perpendicular alignment with the moving object.

2. Select a vantage point to video the event such that you do not have to pan the camera.

3. Include an object of know length in the FOV with the moving object.

4. Keep the FOV constant during the taping.

slide84

All of the video clips included on this CD-ROM have been made using the previous 4 criteria.

Examine the included video clips and you will start to understand how to produce accurate video clips yourself.

Eventually the technique you develop will allow you to collect accurate data from your video clips.