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Hi Andy & All, May 29, 2008
Liquid can flow out only if air can flow in. Air can flow in only
when removal of liquid from the feeder holes generates enough negative
pressure for a bubble of air to enter.
This same principle was used in watering devices for poultry. To see
this in simple form, fill a drinking glass to overflowing, cover it with
a small bowl and invert the assembly. Tip the glass a bit; air bubbles
in and water comes out.
Yt, DW, Kenville
Andy Moir/Chris Callaghan wrote:
> We put out a couple more hummingbird feeders today, and I could not
> come up with a good explanation as to why the water just doesn't drain
> out. I'm sure you all know the type of feeder I'm talking about. A
> plastic container you fill with liquid, then you screw on a red
> plastic part that has four perches and a flower like design. You turn
> the whole thing upside down and hang it. So why doesn't the liquid
> just drain out? Why does it come out for the hummingbirds, but not
> for gravity?
>
> Pondering the truly great question of our time in Freeport, I look
> forward to an answer.
>
> Andy
>
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