Conventional windmills, like the K'Nex tower, spin on a horizontal axis. The rotor, or spinning part of the windmill, is the most important part because it determines how much energy a windmill can capture and then transform into some other form of energy. Drag devices are simple wind machines that use flat, curved or cup-shaped blades to turn the rotor. In these, the wind merely pushes on the cup or blade, forcing the rotor to spin. Lift devices, in contrast, use airfoils like those in the wing of an airplane to propel the rotor.
Air flowing over the blade causes both lift and drag.
As objects, like an airplane's wings, move through the air, the air pulls against them and holds them back. This is called drag. Lift is caused by wind moving at different speeds around the wing. Faster moving air has lower pressure than slowly moving air. Slower air under the wing pushes it upward as lift.