Question by wangyuxing 312 28 tracker: for the first 1 second of my video, the ball's velocity in the x direction fluctuates greatly, may I know why this is so? possible reasons are:
possible reasons are:
compression has a kind of rounding off error to create a sharp image of the basketball.
camera used has some unknown object smoothing causing this effect.
unlikely tracker software has a bug in the calculation of vx.
by the way, I made a video tutorial to explain the physics http://youtu.be/M0N5P0zgFaA without addressing the question, just general graph interpreting using tracker
Measuring g in simple free fall (incorrect values from fits)
Zach Kost-Smith
1 Posts
We are attempting to make a simple measurement of g via a free fall for a high school class. The values given by fits are consistently high (around 11-12 m/s^2 rather than 9.8 m/s^2).
Using the video of projectile motion provided on the website gives the correct value for g. Because of this, we doubt this is a problem with the software itself.
We have tried many things to get this to work including different cameras, orientations (of the camera and meter stick), different balls, locations, backgrounds, lighting levels. We suspect the video source, in particular, we suspect that there is something with the frame rate that causes this issue, but we are unsure. I even went so far as to extract the frames myself (via ffmpeg), mark them via an image editor, and fit the data resulting a value of 12.4 m/s^2 for g.
It looks like the problem is with the video or with the video import, except that the video appears to be fine and looks good after importing into Tracker.
Is there anything that I am missing regarding how to get usable video data into Tracker for quantitative results?
