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Why doesn’t all the water fall out of my hen’s water feeder when I turn it upside down?

When I fill my hen’s water feeder then turn it upside down why doesn’t all the water fall out? Has water got a gravity defying skin?
Ruth Jamieson from Suffolk (Age 55+)

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One Response

  1. This question caught my eye partly because I am ashamed to say that although I have seen hen water feeders many times on my friend’s farm I have never stopped to wonder how they work.

    I guess you are referring to the type of ‘drinker’ that consists of a bottle screwed to a shallow bowl.

    It is all a question of air pressure and surface tension. If you fill a glass with water and turn it upside down the water will fall out due to gravity but if you place a sheet of paper over rim of the glass and hold it in place whilst upturning it the water will not fall out when you take your hand away. It may seem odd that the water does not push the paper down. Air pressure outside the glass is pushing the paper up and at the same time a force called surface tension in the water is creating a seal between the glass and the paper. Try this but remember to do it over the sink in case of failure!!

    With the ‘drinker’ you fill the bottle and screw the bowl to it like a lid. The lid has holes or slots which allow water in to the bowl when the ‘drinker’ is turned over. Some of the water flows out of the bottle into the shallow bowl but as soon as the water level reaches that of the holes surface tension in the water seals the holes and air pressure keeps the water in. When the hens drink some of the water the level falls and the seal is broken and some water flows out of the bottle until the level is high enough again to for surface tension and air pressure to come in to play again.

    After work the other day when I was washing up the tae cups I did a quick experiment to show what happens. I filled a glass with water and turned it over into shallow water in washing up bowl using the upturned glass ‘trick’ described above. I had placed two pencils in the bowl to support the rim of the glass slightly above the base if the bowl. The water did not flow out. With a spoon I removed small amounts of water such as a hen might sip until the water level fell sufficiently for the seal to be broken. Some water flowed out of the glass until the level rose sufficiently to create a seal again round the rim. You can try this.

    So water does not have gravity defying properties but other forces are at work.

    Thanks for a question that made me think about something other than aeroplanes, which do appear to defy gravity, but again there are other forces at work.

    Peter Halford, Science and Technology Teacher, Imperial War Museum Duxford.

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