![]() ![]() Now the weight of the water in the napkin on the empty side exceeds that above the water level in the full glass. When the lowest molecules in the empty glass descend below the water level in the full one, gravity kicks in with a helping hand. Once enough water molecules have crept up and over the rim of the full glass, they begin their descent into the empty one. So capillary action draws the water to the top of the napkin but the siphoning action is due to gravity. Office paper is coated with clay to fill the tiny spaces in an attempt to prevent the same thing from happening. Those water molecules pulled in drag others along because they are also very strongly attracted to each other. Water is pulled up into these spaces by the force of electromagnetic attraction to the cellulose. There are billions of tiny little interconnected spaces between the individual cellulose fibres in your napkin. But again, it's the electromagnetic force driving the show and causing the water to disobey gravity. Capillary is just another name for a narrow tube and that's how this motion gets its name. In a narrow tube, like a glass rod with a tiny hole running through it, the strong attraction to the walls pulls water molecules up to incredible heights. And those molecules pull more water molecules up causing the surface of water in a glass or plastic cup to bow up at the edges and form a concave shape, called a meniscus. That's what makes those molecules in a glass of water on the surface literally creep up walls. And that is why water sticks to itself so incredibly well - it's the electromagnetic attraction between them.īut water molecules are also strongly attracted to many other materials like glass, plastic and paper. Those positive tips on one water molecule are very strongly attracted to the negative poles of two others, and vice versa. Chemists call these electrically charged regions 'poles' (like the North and South Pole) and chemicals that have them are polar molecules. As a result, every water molecule has one slightly negatively electrically charged end and two slightly positively charged tips. Water does because the two hydrogen atoms and single oxygen atom that make up each individual molecule arrange themselves in an electrically nifty way. That fierce attraction is driven by the electromagnetic force which binds every atom in every molecule in the universe together. This surprising behaviour is the result of water's strong affinity for itself and its attraction to countless other materials, like glass, plastic and cellulose. Here's a neat photo demonstrating the same effect in glass straws with some really tiny internal diameters. You can verify this fact with one of those tiny bendy straws you find on the side of a single serve fruit juice carton. What you might not have noticed is that the thinner the straw, the higher the water climbs up inside. Look carefully and you'll notice the water level inside the straw is always slightly higher than the water surface outside. The same thing happens to a lesser extent in a drinking straw resting in a glass of water. That's capillary action at work but what exactly causes the water to disobey gravity with such reckless abandon? You've probably noticed that water instantly races up and into the fabric of a paper napkin or tissue upon the slightest contact. It's called capillary action and it is no exaggeration to say that you and I would not be here without it. Your Christmas napkin siphon may be unbearably slow but the science that makes it work is another one of those marvellous yet frequently overlooked wonders of the natural world. Now pop those socks in a drawer and get back to your nuclear fusion research. In the meantime, congratulations! You've survived another Christmas lunch. If you want to completely drain the first glass, simply elevate it above the other. ![]() This should occur just as the pudding arrives. ![]() When the levels in both glasses are equal, the siphon stops working and the show is over. By my calculations, it should be about a quarter full by Aunty Beryl's third helping.ĥ. It's about as thrilling as watching the grass grow but water will slowly flow up the napkin and into the empty glass. Now sit back and let the good times flow.Ĥ. Believe it or not, you've just made a siphon. Dip one end of the napkin into the full glass and put the other inside the empty glass. Roll your napkin into a long piece of rope (a little turkey grease won't affect your siphon's performance).ģ. I've added green food colouring to my water for a little seasonal pizzazz.Ģ. You'll need two glasses, a napkin, some water and a bucketload of patience. Christmas napkin siphon trick, Science Online, ġ. ![]()
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