Wash out an empty soda can and let it dry upside down. Once dry, use a razor blade to cut the top off the can just under the ridge.
Use scissors to cut down from the top edge to 1/4 inch from the bottom of the can. Make the cuts every 1/4 to 1/2 inch, depending on how wide you want the strips to be. The cuts can be straight, or may zigzag. Bend the resulting strips of metal outward, forming a pinwheel shape.
Drill a hole in the center of a plastic bottle cap and one in the center bottom of the can.
Thread fishing line through the hole in the bottle cap, from the outside to the inside. Tie a knot in the outside end. Fish the other end of the fishing line through the hole in the bottom of the can, from outside to the inside. Tie another knot, but do not cut the excess string.
Tie the completed pinwheel, using the excess string, to a long, narrow stick such as a chopstick or a skewer. Plant the stick in the ground and the wind will spin your pinwheel.