The applet on Page 2 simulates the forces acting on a vertically acceleratinging block. The block is supported by springs that in turn are resting on a platform. The platform can move upward or downward. The situation simulated by the applet is analogous to that of a person standing on a bathroom scale in an accelerating elevator.

The system can be viewed both in the inertial Lab frame and the non-inertial CM frame. The free-body diagrams corresponding to each frame can be displayed.

For detailed information on how to use the applet, please go to Applet Help on the applet's Help menu. A Lesson on the normal force is also available from the Help menu.