TrackXY
Track & log x & y displacement, in realtime, of object in webcam
... other ready-made program that would track an object in real-time from webcam, other than an $80 special-purpose program used in the original (torsion balance) experiment we were replicating. I released TrackXY to reduce barriers to entry to science.
Planned features include versions for each platform, a GUI, comprehensive data management, and data analysis tools.
To analyze motion in /recorded/ video (not real-time), you may prefer something like PhysMo, also a SourceForge project.