Weigh to go !

The BLUE scale is placed on top pf the PURPLE scale and the purple scale is adjusted to read ZERO. The GREEN scale is hung from the YELLOW scale and the yellow scale is adjusted to read ZERO. You can place the 6 kilogram mass on each of the scales by dragging it to the scale. The applet will show you the scale readings. Can you explain the readings? Is your explanation a model of the data? Is it a model of why the scales work as they do? What questions would/could you pose to your students based on this applet?