Re: El Nino assignment

Author Subject: Re: El Nino assignment
Dallas Campbell Posted At 01:08:01 10/29/2000
One reason why doors and windows stick when the weather is wet is because of the change in the dimensions of their wood frames. Wood is composed of cellulose fibers that have voids or air pockets in them. Because our climate is so dry, the moisture that would normally be in the voids evaporates out, which causes shrinkage of the wood, especially in the width dimension.
When storms approach, the relative humidity in the air increases and the wood fibers begin to absorb moisture because of the increased number of water droplets in the air. As the fibers absorb moisture, they swell which causes the wood in the door or window frame, and its wood casing, to expand. The gap between the door or window and its casing is reduced and, in some cases, disappears. That contact makes them harder to open because they rub against their casings.
Because both surfaces, the door and the casing, are usually painted, it is even harder to open, as the paint tends to bond or adhere. In effect, it is glued shut. After a shower passes and the air begins to dry, the moisture in the wood begins to evaporate out, the door shrinks and no longer contacts the casing and sticking stops.
A control for the experiment would be a metal door and casing, which do not absorb moisture and do not expand. Another way to measure the change in the distance between the door and casing, in addition to the method you propose, would be a feeler gauge, which takes an internal measurement of distance between two proximate objects. A tape measure could also be used to measure any changes in the dimensions of the door or window itself.
I can contribute anecdotal data to the experiment. Thursday evening, about two hours prior to the start of the rain storm, a door in my house began to stick. In addition, the redwood gate to my backyard also began to stick. (Redwood is very soft and expands a lot when it absorbs lots of moisture.) The door continued to stick until Friday afternoon, when the humidity had dropped. The wood on the gate is thicker and will lose its moisture slower.
Good luck

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