Photo: mikebrogan (Flickr)
Want to impress your friends with a cool candle trick? Tell them that you’re going to blow on a candle flame and make it come toward you rather than lean away or even go out. Then you’ll top that off by blowing out the candle with a bottle between you and the flame. They’ll have their doubts, but you’ll impress them in the end.
Get a business card or a playing card and hold it between your mouth and a lighted candle, about two inches from the candle flame. Now blow against the center of the card. Amazingly, the candle flame will lean toward the card, not away it.
A moving stream of air – or any other fluid – has lower pressure than the still atmosphere around it. In this candle trick, fast-moving air around the edges of the card makes low air pressure on the other side of the card. Atmospheric pressure on the far side of the candle pushes air toward the card, and the flame moves in response to that air.
Now pick up the wine bottle – or the soft-drink bottle or the ketchup bottle, depending on what kind of dinner it is – and hold the bottle between you and the candle. Blow against the side of the bottle. The round shape of the bottle is streamlined–the shape makes it easy for air currents from your breath to rejoin on the other side of the bottle and continue toward the flame. The candle will be blown out as if the bottle weren’t there at all.