Video Analysis Activity - Dr. Carlson's Course Webpages



Video Analysis Activity Name ____________________________________

Physics

Purpose: To import a video into Logger Pro and use the analyzing tools to explore projectile motion.

Equipment: Video file, Logger Pro, calculator, graph paper, ruler, protractor

Logger Pro is a powerful analysis program that not only allows us to take real-time data from sensors, but also allows us to use a movie to analyze motion. However, there are a few key elements to the video that must exist for us to use Logger Pro:

1. The video frame must stay still. It cannot pan left to right or zoom in or out during the section to be analyzed.

2. The video must have an object in it’s frame that has a known length. This is a must since Logger Pro uses the size and number of pixels to determine actual length. The easiest is to place a meterstick on the ground that will be fully visible in the frame.

3. The motion that is being analyzed must stay at the same distance from the camera the entire time. You cannot determine someone’s speed who is running away from the camera… only parallel to the camera.

4. The video clips used must be stored as “mov” files for Logger Pro to properly read them.

Procedure:

1. Open Logger Pro from the desktop of your computer.

If you are using a video which is pre-stored for you, follow steps 2 -3. If you are taking video directly from a camera, follow steps 4 -5.

2. Under the “Insert” menu in Logger Pro, select “movie”.

3. Open internet explorer. Type physics in the address bar. Under the “Logger Pro” file, open “Logger Pro Video Files” and select one of the Projectile videos to open. Save the logger pro file in your student drive just in case!

4. Cue up your video tape and attach the camera to the laptop with the mini fire-wire cable.

5. Under the “Insert” menu in Logger pro, select “Video Capture”. Start and stop the capture with the controls and the movie will be automatically loaded into Logger pro. I would suggest only importing the small amount of video that shows the projectile motion, or else you will have issues with Logger Pro and memory.

6. Save the logger pro file just in case!

7. Now that you have the video open in Logger Pro and saved, it is time to take a few measurements! We will start with telling Logger Pro what length measurement we know. First, click on the button in the lower right-hand corner of the screen which looks like this: This should open a whole row of buttons on the right of the screen.

8. Next, select the button which looks like a meterstick. [pic] Click and drag over the meterstick in your video. A green line should appear over the meterstick and a box will pop open to ask you the measurement. Be sure it says 1 meter.

9. Now move the video to where the projectile is released. Click on the “Add Point” tool: [pic] Then click in the center of your projectile to create a blue dot. The video should automatically move to the next frame. Continue to add these blue points to the center of your projectile the entire time it is in the air on the video. Stop before it hits the ground or is caught in the video. Once you have finished, your video should look something like this:

10. Once all your data points are added, we will want to set where the origin of the graph will be. We want this to be the starting point of the rocket in the video. To set the origin, select the “Set Origin” tool ( [pic]) and then click on where the projectile was launched. Try to keep the X and Y axis (yellow lines) as straight as you can in the frame.

11. Once you have added all the points and the origin, click on the [pic] button to synchronize the data to your video. Now whenever you play the video, the data will play with it. Also, if you move your mouse through the data, the video will move also! Hint: using ctrl+R will rearrange the windows so they all fit nicely within LoggerPro

ANALYSIS:

Now we are going to use the data taken through the video to do a few calculations and answer a few questions! Show all the graphs you make in the document you turn in on cybergate. (copy and paste them here)

1. Use the data from the video to determine the following in formation. You can use the numbers from the cells on the left , the examine tool on the graphs ([pic]) , the measuring tool on the video ([pic]) or any other method you can figure out by playing around with the program!

|The hang-time of the projectile (be sure to measure from after it was released to just BEFORE it| |

|hits the ground. | |

|The height above the ground from which the projectile was released. | |

|The range of the projectile. | |

|The initial X velocity of the projectile (again after it was released) | |

|The initial Y velocity of the projectile | |

|The FINAL X velocity just before it hits the ground or is caught | |

|The FINAL Y velocity just before it hits the ground or is caught | |

2. Click on the graph area of Logger Pro. Click on the Y-axis label and change this to “X”. This will display the “X” distance vs. time. What does this graph tell you about the X distance the projectile traveled?

Use the linear fit tool ([pic]) to determine the slope of this line where you are interested in it (aka after it starts to move). Slope = ____________________

3. Click on the Y-axis label and choose “ X velocity”. Describe what this graph is showing regarding the velocity of the projectile in the X direction.

Use the STAT tool ([pic]) and find the mean value for the X velocity. Mean = __________________

How does the mean X velocity relate to the Slope of the X distance graph?

4. Change the graph now to “Y” distance vs. time. Describe what this graph tells you about the rocket’s motion in the Y direction.

How does the Y distance at point where the projectile was released compare to the measurement you made with the ruler on the video?

5. Change the graph to the “Y Velocity”. How does this graph show what happens to the vertical velocity of the projectile while it is in the air? Describe all parts of the graph including where it starts, where it ends, and what happens between that!

Use the linear fit tool to determine the slope of this line. Slope = _____________________

What SHOULD be the slope of the Y Velocity line??

6. What is the Y velocity of the projectile at the highest point in its trajectory?

7. Using the equation to find ∆x, fill in the hang-time of the projectile and the mean X velocity from question # 3, and CALCULATE the range of the projectile. SHOW WORK BELOW:

∆x = __________________

How does this calculated range compare to the measured range in your data table from #1?

8. Use the equation for finding ∆y and fill in your hang-time and the INITIAL Y velocity from your data table. CALCULATE ∆y. SHOW WORK BELOW:

∆y = ___________________

What does this calculated ∆y value represent? Does it make sense?

9. One last calculation!!! Now we want to use the initial X and Y velocities and find the TOTAL initial velocity. Remember the vector triangle! We want the hypotenuse! We also want the ANGLE at which the projectile was launched. You can do both of these using TRIG, SHOW ALL YOUR WORK!!! That means you will need to insert equations. Click on insert in Word and choose equation. You may have to insert multiple equations.

Total initial velocity (vi) = ___________________ Angle of launch = _________________

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