Push three pins into the middle of a piece of wood and lay a coin 5 new pence or 25 cents on top of them. You can make a bet! Nobody who does not know the experiment will be able to blow the coin off the tripod.The metal cannot hold the gust of air on its narrow,smooth edges. The gust shoots through under the coin and reduces the air pressure, forcing the coin more firmly on to the pins. But if you lay your chin on the wood just in front of the coin and blow with your lower lip pushed forward, the air hits the underside of the coin directly and lifts it off.