The old and the new

Today I went on a field trip with students in our Environmental Studies department. We took them to see an old grist mill and a new wind turbine. We also got to see an old windmill that was used to pump water. It was part of a greater Earth Day / week festivities in our area. It was interesting to see various types of windmills that ground wheat for flour, pumped water for livestock, and generated electricity for a community college. The old grist mill had cloth sails, but they could not be put on because the winds were around 15-20 miles per hour and that was too strong. The winds had to be between 5-10 m.p.h. Who knew? The water pumping windmill would operate regardless of the wind speed. The modern wind turbine had to have winds over 3 m.p.h. but not more than 80.