Science Projects And Inventions

YOU  NEED:

• A square cheese cracker
• A square of paper
• A pencil with eraser
• A pin

Between the tips of your thumb and middle finger lightly hold the square cheese cracker. It will begin In rotate as you blow on it. Try and make a turning pinwheel. Take a 5-inch (11.25cm) square of paper, as shown in the illustration. Deftly fold the corners of the paper Insert a pin at the end of the pencil which has the eraser. Now flail the pencil around in the air. The paper square will start to rotate. Now try and pull the pinwheel in a backward position. It will begin to rotate in the opposite direction. Drag the pinwheel backward and it will spin in opposite direction.

HOW DOES IT WORK?

Air pressure is created which pushes on the surface of the cracker once you blow on it. If the air pressure is greater on one side -- for instance i in the top that section will start to move away from you. The other part comes towards you. When the cracker turns on its side once you blow on it, the thin edge creates much less resistance. The cracker will turn easily past this point and show you its flip side if your breath is strong enough. Because it is closer to you the strength of your breath is greater rotating cracker. If you carry on blowing on the cracker it gathers speed mid continues to twirl. The same principle applies for the pinwheel. Pressure is created when the pinwheel is waved in the air. The strength of the air on the flat surface of the paper is much larger than that on the thin edge. The pinwheel gathers momentum and can rotate freely It you flail it around quickly so that it generates sufficient motion. It is thus capable of overcoming the resistance brought about by the thin edge.