You can explore energy rules by participating in many of the activities located in other units. For example, learn more about conversions and energy “loss” by exploring the Unit: What is Energy? Section D. Activities and Experiments.
Since a motor converts electrical energy into mechanical energy and a generator converts mechanical into electrical energy, it should be possible to connect a motor to an equally sized generator so that they would supply energy to each other and run forever.
This arrangement is one example of a perpetual motion machine and such machines are not possible according to the laws of thermodynamics. The motor-generator arrangement described above violates the second law of thermodynamics.
A light connected to a solar cell. All the light from the light bulb shines on the solar cell, which makes electricity that goes into the light bulb, which lights the light bulb, and the light shines on the solar cell, and so on.
Would this example work? No, the light will not keep shining because some of the electricity is converted to heat, not light. The solar cell probably doesn’t convert all the light to electricity. Some of the electricity is lost in heating the wires between the cell and the bulb. Again the solar cell-light bulb arrangement described above violates the second law of thermodynamics. (Excerpts taken from KEEP Energy Education Activity Guide “Energy Sparks.”)
There are other ways to demonstrate how “energy rules.” A misguided entrepreneur thought he could raise cats for their fur and use rats as the food source for the cats. He had the bright idea that he would not have to buy food for the rats because the rodents could eat the deskinned cats. Voila! The cats eat the rats and the rats eat the cats.
The silly furrier was thinking he was in a closed loop system with nothing being lost, but something was being lost. Energy! Both the cats and rats were emitting heat (and other waste materials) that were not in balance with what was gained from their food sources.