Tracker is a free video analysis and modeling tool built on the Open Source Physics (OSP) Java framework. It is designed to be used in physics education. Tracker video modeling is a powerful way to combine videos with computer modeling. Tracker Features Tracking: Manual and automated object tracking with position, velocity and acceleration overlays and data. Center of mass tracks. Interactive graphical vectors and vector sums. RGB line profiles at any angle, time-dependent RGB regions. Modeling: Model Builder creates kinematic and dynamic models of point mass particles and two-body systems. External models animate and overlay multi-point data from separate modeling programs such as spreadsheets and Easy Java Simulations. Model overlays are automatically synchronized and scaled to the video for direct visual comparison with the real world.