A weather vane tells two things--which way is north and which direction the wind is coming from. As long as it tells of those two things, a weather vane can be as plain or fancy as you wish. Weather vanes make good first science projects for children to use to learn to measure and understand the world around them. They can use a weather vane as a jumping off point to explore the history of the decorative symbols used to top them or delve more deeply into the physics of wind and barometric pressure. Or you can just have fun together making one.
Design and cut your vane and directional symbols with tin snips. Whether you make an arrow or some other symbol like an eagle, rooster or horse, your vane should have fewer square inches or area on the arrow or head end and more on the tail. The head of your vane point will swing around to point into the wind to tell you where the wind is coming from. Cut two identical shapes out of the metal for the vane. Cut a symbol for each cardinal direction: north, south, east, west.
Make your support pole, using a broomstick or other round pole that has a top that you can sand or cut to a rounded point to fit inside the jar or can. Find a place to mount the pole in a location where it can catch the wind, unobstructed by trees or buildings. A fence post or yard shed are good places to try.
Attach short sections of dowel rods and secure them at 90-degree angles to a support pole, using foam and glue or papier mache. If your support pole is thick enough, you can simply drill holes, run the dowels through and glue them in place in the pole. Be sure to leave enough room at the top of the pole to slip the olive jar or tin can over the pole. Attach your cardinal direction (N-S, E-W) indicators to the ends of the dowels with tacks or staples. Paint or lacquer any paper mache or foam on the assembled pole to protect it from moisture.
Attach your vane to the (bottom-up) olive jar by shaping the center of each piece around the jar and securing each side with clips or grommets. If you are using a shape such as a rooster for your vane, you'll want to set the jar a bit further up into the shape so that it will balance properly and not tip over. It's also important to balance your vane so that it has the same weight fore and aft--on each side of the jar. This means that you'll have to position the jar a bit closer to the tail of the vane than its head, since there's more area on the tail. Set the vane on top of the support pole and the wind will catch the tail and bring the head around to point in the direction the wind comes from.