How does the electric force between charged objects depend on the distance between them? Use this video of two charged spheres to find out. One is hanging from a string, the other is mounted on a rod. Start by just playing the video. If all else fails, click the Instructions button.
| x (?) | y (?) |
This action will erase the current data set.
Is that what you want to to?
The basic idea is pretty straightforward: calibrate the image, set the origin, step through the video by clicking on points you want to record, and finally upload your data to the clipboard. Because there are two objects in this video whose position you want, you will need to record (and copy/paste) two sets of data. Calibration and setting the origin only need to be done once.
There are four buttons. From left to right they are: a button to rewind to the start, the play button, a button to step one frame backward, and a button to step one frame foward.
Press this button to start the calibration button. Click on the video where you want to start defining a line of known length, then click again where you want that line to end. Enter the actual length of this line and the units for that length in the popup window. The units in the data table headings will be updated to reflect your input.
If for some reason you don't like your calibration, you can just hit the button again. Be aware that if you have started taking data, re-calibrating will erase it.
Setting the origin is optional. If you don't, the point (0,0) will be in the upper left corner of the image. The zeroes for the x and y directions are set separately.
As with the calibration, you can reset the origin at any time, but you will lose your already acquired data if you have any.
Click the "Get position data" to start the process. The cursor will change to a conveniently shaped cross-hair. Position it over the sphere whose position you want to follow, and click the mouse. The app will record the position, draw a red dot at that position, and automatically advance the video to the next frame. (You can use the video controls to skip additional frames, or to skip backwards.)
Click the Done button when you have finished, or Cancel to erase all your data and start over. (This does not affect the calibration or zero point.)
To get a second data set (for the other sphere, for example), clicking the Get position data button again. You do not need to re-calibrate or re-set the zero position.
Acquiring a new set of data means erasing the old set. Be sure you have copied that data to the clipboard (and pasted it into a spreadsheet!) before proceeding. If, for some reason, you want to save the old data, you will still have to copy it to the clipboard. Just don't bother to paste it somwhere. It will be overwritten by next time you copy data to the clipboard.
The Copy data to clipboard button does just what it says. The data is written as plain text in a tab-delimitted format, which means you can switch to a spreadsheet application (like Sheets or Excel) and hit "paste" to put a copy of the data there.
Electric Force Video Analysis v1.00
© Geoff Nunes, 2022
Questions, brickbats, and requests for new features can be sent to doc at this website (noragulfa.com). Please don't expect a rapid response.
Video loaded from Rochester Institute of Technology Used by permission.
Change Log
v1.00
Initial release: Aug. 4, 2022