A free-body diagram is a diagram showing all the forces that are being applied to an object.
With this simulation, you can practice sketching free-body diagrams for a one-dimensional situation. In this activity, two boxes are stacked so that one box is on top of the other. The bottom box rests on the floor of an elevator, and the elevator may be at rest, moving with a constant velocity, or accelerating.
You need to sketch three free-body diagrams: