A quantitative illustration of how non-renewable resources are depleted while renewable resources continue to provide energy. Students remove beads (units of energy) from a bag (representing a country). A certain number of beads are removed from the bag each "year." At some point, no non-renewable beads remain. Student groups have different ratios of renewable and non-renewable energy beads. A comparison of the remaining beads and time when they ran out of energy shows the value of utilizing a greater proportion of renewable resources as a sustainable energy resources.