Using Tracker on a Mac

It's an open source program that deserves more than a few minutes of your time. Rotating axes is VERY EASY. Following the instructions below will take you less than 10 minutes, I'm sure.

Note: the ctrl-click problem is Mac-specific and I hope that Doug Brown will change the method used to mark the object or that Apple will use cmd-click instead of ctrl-click as the right-click, but there's little chance that Apple would change this.

To get around this annoyance, do the following (note that I include all steps from the beginning):

(1) open the video; I used a video that came with tracker, FlexTrackRaces.mov.

(2) Click the "show axes" icon in the toolbar (note: it looks like a red set of axes like "_|_").

(3) Drag the origin of the coordinate system to the top of the inclined part of the ramp.

(4) Grab the small vertical line on the +x axis ( it looks like "|" ) and rotate the coordinate system so that the +x axis is parallel to the ramp.

(5) Click the "show axes" icon again in order to hide the axes.

(6) Click the "show track control" icon (it has the asterisk in the icon) in the toolbar. A new floating toolbar called Track Control will appear.

(7) Click the "New" button in the Track Control toolbar and choose "Point Mass" from the menu.

(8) Click the "mass A" button that now appears on the Track Control toolbar and select "Mark by Default" from the menu for mass A.

(9) Step the video forward to the point where the ball is at the top of the incilne; use the step forward button on the video player buttons beneath the video.

(10) Click on the ball to mark it; it will advance to the next frame; continue clicking.

(11) To view the graph, find the very small button (it looks like a small circle) at the center of the bottom of the window frame (below the video player) that is used to adjust the height of the bottom edge of the window. Click and drag this button upward so that there are now two frames showing.

(12) At the top left corner of this new frame (bottom frame), there is an icon showing a set of axes ( _|_ ). Click this icon and select "Plot View" from the menu.

(13) You'll see the x vs. t graph that is linear.

(14) To view multiple graphs or datatables, etc., grab the small button on the left edge of this bottom window frame and drag it to the right. It then shows a new window frame on the left and you can use it to view results of data analysis or whatever.

Note that I should have set the scale first. This can be done by clicking the tape measure icon in the main toolbar (it looks like "<--10-->"). Then you can drag the ends and double click the center to change the value.

Note that you'll have to take off the "Mark by Default" setting on Mass A if you want to do anything else on the video screen such as changing the scale. Otherwise, it thinks that you are making the object in the video. Once again, using "Mark by Default" in this case is an annoyance that is solely due to the fact that ctrl-click will not mark the object on a Mac OS.

This is open source software and it gets better due to the collective efforts of its community of users and the developer(s). Doug is a really great guy and has poured a lot of time into this project, solely for our benefit. I encourage you to use this software and give him constructive feedback. Maybe you can even help contribute to the documentation.

I agree that finding the graph window is extraordinarily difficult the first time you use the program. However, once you know how to do it, you'll never forget it. I hope that Doug will address this issue in the documentation or in the program itself.