A windmill does work by harnessing the energy of moving air. Its name is derived from its initial use -- the grinding or milling of grain -- though windmills have also been used to pump water uphill, behind dikes, and into rivers flowing to the sea. You may be familiar with the classical windmill design, which features a rotor composed of four wooden panels with cloth stretched over them. Today, much larger wind generators called wind turbines are widely used to produce electricity to power homes, businesses, and city buildings and services.

Although windmills and wind turbines vary in design, they operate in the same basic way. Kinetic energy carried in the wind is translated into rotational motion of the blades, which are attached to a rotor hub assembly atop a tall structure. Some rotor blades are designed like airplane wings so that wind passing over and under the blades creates a pressure differential that generates a lifting force. Other, flatter blade designs simply allow the wind to push them. These are known as drag devices. Whichever design is used, it's essential that the blades rotate at a rate of speed that optimizes energy transfer -- neither too quickly nor too slowly.

In the activity presented in this video segment, ZOOM cast members are challenged to design a paper windmill able to lift a small load from the floor to tabletop height. As they test their windmill, they observe some problems with their initial design and then discuss how to correct at least one of them. To prevent the load from spilling out of the container, which tumbles forward as it's lifted, they cover it with tape. They also could have made adjustments to the way the string wound on the crank mechanism so that it didn't impede the lifting progress. This probably would have avoided the need to turn the hair dryer up to a higher setting. The process of testing a design in a performance setting and then returning to the design stage to make modifications is a critical part of the engineering design process.