A wind vane is a mechanical device that shows the direction the wind is blowing. Although it can be built with a variety of materials, the idea behind the design is the same: to accurately tell wind direction. A simple wind vane has an arrow on one end and a tail on the other, with the arrow smaller than the tail. If constructed correctly, the arrow will position itself to point in the direction the wind is blowing from.
Fill a plastic soda bottle with dirt, sand or small pebbles to create a stable base.
Make four marks near the top of the bottle equal spaces apart. Make an "N" to represent north, "W" to represent west, "E" to represent east and "S" to represent south.
Cut out two pieces of cardboard. One piece, the tail, should be a square 3 inches long by 3 inches wide. The other piece, the point, should be in the shape of a triangle. Cut the triangle 2 inches high at the wide end. The size of the point is not important, as long as it is smaller than the tail.
Tape the tail and point to each end of the straw by laying the two pieces of cardboard on the table and laying the straw over them. Position the cardboard pieces under each end of the straw and cover the ends of the straw with a piece of tape long enough to hold each end of the straw to the cardboard.
Push the straight pin through the exact middle of the straw, then push the end of the pin into the eraser at the end of the pencil. Stick the pencil into the dirt or pebbles inside the bottle. The straw should be able to move freely back and forth. The moving part is called the wind vane.
Take the bottle with the wind vane attached outside. Find north by holding a compass in one hand and moving your body until the needle is lined up with north. Position the wind vane so the N written on the bottle is lined up with the same north as the compass. If you don't have a compass and the setting sun is on your left and the rising sun is on your right, you are facing north.