How Windmills Work

Video Transcript

"Hi, I'm Steve Jones, and I'm going to explain how windmills work. Well, we've all seen the familiar diagram pictures of windmills, particularly in Holland, which were actually designed to pump water, out of waterlogged fields. They all have the same construction, a large body of a house, with a movable top. This top rotates, and a set of sails, they're called sails, because they're literally sails, as on a sailing ship. They are canvassed sails over a wooden frame, and at the back, there was also quite a large sail, which tended to rotate the top of the mill in the right direction, to keep the wind coming in the right direction, so it was basically how the windmill was constructed. It depended on the wind direction, it depended on the wind speed. One important thing is, that these big sails aren't going to go around fast. They're going to go around quite slowly, and therefore, you can't connect them direct to a machine, because it would work too slowly. You need a gearing system, that is a small wheel and a big wheel, put together, so that when the big wheel rotates once, the small wheel on the side, rotates many, many times, so this is called gearing up. You would gear up, and the rotating shaft would be rotating quickly at the bottom, even though the sails were rotating slowly. Now, the question is, why do the sails rotate? Well, here we have a diagram of a sail, and here is the wind. Well, if the wind is blowing, you would expect the sail to go that way, or some way. The main thing is that this sail is fixed, and it cannot move in this direction. It can move that way, or it can move that way, and therefore, when the wind is blowing in this direction, even though it's not blowing straight onto the sail, and the sail isn't in this position, it is still forcing the sail to move, and it will be forced to move in that direction, just as on a sailing ship, and in fact, it's the fact that this point is fixed, that the thing will rotate, so basically, a windmill works by using the wind to drive the sails, by this process, and then the sail's rotation is geared up, so that the rotation can be used to drive machines, and typically of course, grindstones for grinding corn, or pumps for pumping water, so that is basically how windmills work."