Wind energy! This is one energy form which humans have been using for several centuries. It is a type of mechanical energy, which means it is energy derived from motion. Do you know how the wind is caused? Ultimately, it is due to the Sun. The energy of the Sun heats up different parts of the air in the earth's atmosphere unevenly.
The farther you are from the equator, the lesser is the amount of the Sun's energy reaching the surface. This difference of heating causes the air in some places to get heated more, whereas the air in some other parts is still "colder." Since warm air is lighter than cold air, the warmer air rises up leaving a void which is taken up by cold air moving in from nearby places.
This movement of air is the wind. Since the earth is also rotating at the same time, the air also moves across the surface of the earth causing wind. The same principle can happen locally too, especially near the sea.
Sand gets heated much more faster than water, and so during the day the air above the sand (on land) gets hotter faster and tends to rise up. The air above the water is still cooler and moves in towards the land, causing a breeze during daytime.
At night, the reverse occurs as the sand cools off faster but the water still has some warmth gained during the day. So the air above the water is warm and now rises up, and the air from the land flows towards the sea.
The power of the wind has been used for moving boats, grinding grains or drawing water for several hundred years. It is now used to generate electricity too. The windmills are like reverse fans. Wind mills typically have 2-3 blades (called turbine blades) and one generator.
The moving blades rotate a magnet which is housed inside set of copper wires. When a magnet rotates inside the copper wire, it causes electricity to flow in the copper due to magnetism. Thus electricity is generated. In Pennsylvania, Somerset county & Williamsport are good places for wind power. When a lot of windmills are together at one place they are called wind farms!
For information on wind energy see the website by the US Department of Energy: http://www.eia.doe.gov/kids/energyfacts/sources/renewable/wind.html and the website by Alliant at http://www.powerhousekids.com Look under Fun & Games (purple menu bar on webpage) for "Cool Projects to Try at Home."
Little Lion Experiment:
We will learn how to make a small wind runner or wind fan. You will need some paper (from any notebook or copier) or long slender leaves (optional), a thumbtack, a pencil with eraser at one end, and scissors.
You can make wind runners using long slender leaves or paper. For making a wind runner using a leaf, please see the diagram which illustrates how to cut off one half of the leaf on either side of the center line leaving some space in the middle to make a hole. It is best to pick slender leaves that are green, a bit sturdy and have a smooth edge all along.
You can then pierce a small hole with a thumbtack through the hole and push it into the eraser of a pencil on the other end. Once the leaf is secure between the tack and the pencil, run around and see the leaf rotate like a fan. You can also try fixing this to your bicycle handle bar and watch it spin fast!