In this simulation a bar is supported on two scales that provide their readings in grams. Three different mass bars can be chosen. When choosing a bar, it is placed on the two scales that are initially located under the ends of the bar (0 cm position and 100 cm position). With a bar placed on the scales, the scales can be moved under the bar to a point where there is still balance. In some situations, some moves are not allowed. This occurs because if the scale were moved beyond this point, the bar would tip! (There would be no balance). A “Weight” can be placed on the bar. There are three “Weights” options. When choosing one of the weights, it is placed on the bar in the central position (50 cm). Scales are initially located under the ends of the bar. The positions of the scales under the bar and the position of the “Weight” over the bar can be changed. Remember that the positions can only be set up to the point where there is still balance. The simulation also allows you to determine the system's center of mass or center of gravity by placing a scale directly under it.