How do you get position and time data for an object in motion? In previous labs, you have done this with either the drop timer or the motion detector. There is another way, video analysis. In video analysis, you will use a program to mark an object in each frame of a video. This will give 2-dimensional position data (both x and y) as well as time. With this data you can analyze it as you please.
I think the best way to look at video analysis is with an example. I am going to use a free java-based video analysis program called Tracker Video. So, to start, you can run that program. You will also need a video to analyze. I am going to use one from the LivePhoto Physics project - the howitzer cart.
On that page, just save the video to somewhere you can find it on your computer. Back in Tracker, click video-import
Then browse to the location of the saved howitzer movie. From there, you should be able to follow along with this video tutorial.
Basically, you are going to do the following:
- Scale the video using the tape measure tool and the size of the video (14.2 cm marks).
- Set the frame rate of the video
- Mark the location of the ball in each frame
- Mark the location of the cart in each frame
- Analyze the data in some way
For this particular video, you should be able to answer the following questions:
- What is the vertical acceleration of the ball?
- What is the horizontal acceleration of the ball?
- What is the horizontal velocity of the ball?
- What is the horizontal acceleration of the cart?
- What is the horizontal velocity of the cart?
- How do the horizontal velocity of the cart and the ball compare?
So, when you are doing video analysis, it should be for a reason. In this case, it was to compare the horizontal velocities of the cart and ball and perhaps explain why the ball lands in the cart when launched.
After you play around with that video, try another analysis. Here are some sources for some movies to look at:
- LivePhoto Project
- Videos from Tracker Video - go to download mechanics videos (it is a zip file)
- Youtube - yes, there are some great and interesting videos you can analyze from youtube. First, you will have to download the video. There are tons of ways to do this, you can find one you like if you google “how to download youtube videos”. I used to use kickyoutube.com - but sometimes that doesn’t work. When you get a video from the internet, consider the following:
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- Does the camera pan or zoom during the motion of interest? If so, this will be a much more difficult video to analyze (but it can be done).
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- Can you find the scale of the video? There should be something in the video that you know the size of.
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- Is the motion you are exploring perpendicular to the camera? If the object is moving towards or away from the camera, you would have to take into account perspective (a difficult thing to do).
Here are some more examples of videos I have analyzed
- Blob Jump Analysis
- Kobe Bryant Jumping over a car
- The Physics of Line Rider
- Analysis of Ford F-150 Commercial - stopping a plane
- Kobe Bryant Jumping over snakes
- Can an exploding hammer lift a guy?
Finally, here is another video tutorial.