Genre: Forum

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. In article , Peter Jason wrote: A vacuum will hold up a column of water about 10 meters, so how does water get to the top of very tall trees? Peter The water isn't held up by vacuum (actually the external air pressure, not the vacuum per se) but by capillary action in series of very fine tubes. The cohesion of the water molecules to each other is what keeps the water up and rising as water evaporates from the periphery of the tree. N.B. This is why you cut off the bottom of flower stems before you put the bouquet in water. Thank you. I was also wondering why water evaporates more quickly from cotton (cellulosic) materials faster than from polyester, nylon, glass wool, and rubber foam etc. Indeed the difference is quite marked. As an experiment I put a petri dish on to a balance and in its center weighed a 1 gram piece of various substrates such as filter paper, cotton wool, cotton pajamas, nylon rope, glass wick, canvas, orlon and the like. In the center of these materials I placed 1gm of distilled water. In all cases the cellulose materials dried much faster than any other. Almost twice as fast. Strange, because this is the opposite I expected given the OH groups on the cellulose and their likely hood of their forming H-bonds with the water and so retaining it. EG a nylon shirt will dry faster than a cotton one, or so it seems though evidently the nylon article will contain less water when wet. I suggest you look at your samples both dry and wet with varying amounts of water under a low power microscope. Most of the fibers you list do not absorb water, so the limited amount of water you used just sits between the threads. THis causes a great deal less water surface to be exposed to air than if it is absorbed into cotton threads. Note that the diameter of the fibers of these materials and the tightness of the weave or twist are important factors and should be controlled for, as is the thickness or surface area to volume ratio of the samples. Also, what was your endpoint for determining that the sample was dry again? It should be the sample returning to a weight of 1 gram, and you should control for air motion, temperature and humidity. A nylon shirt will dry faster than a cotton one because it holds less water after being washed. You might want to experiment with weighing samples of various materials before and after being immersed in water and wrung, squeezed or spun out. You might be interested to examine wool fibers carefully both wet and dry. Like hair, they are covered with overlapping scales that remain from the cells they are composed of. Wool fibers absorb water and swell, trapping it. This explains why wool fabric is slow to dry and why it is unique in textile fibers for making garments that are warm even when they are wet. See if your library has any books on textiles and textile fibers. I've got a book I picked up at a rummage sale that is the text for a community college course in textile science, and the description of how synthetic and natural fibers are prepared, spun and woven is very interesting. Developments in the past few decades have made some surprising changes from the straightforward mechanization of techniques that go back for millennia. For example, weft fibers can be spun into thread by air currents as the fabric is woven in sealed looms, and non-woven textiles with a wide range of properties are becoming more common for both traditional and innovative uses. A nylon shirt will dry faster than a cotton one because it holds less water after being washed. You might want to experiment with weighing samples of various materials before and after being immersed in water and wrung, squeezed or spun out. You might be interested to examine wool fibers carefully both wet and dry. Like hair, they are covered with overlapping scales that remain from the cells they are composed of. Wool fibers absorb water and swell, trapping it. This explains why wool fabric is slow to dry and why it is unique in textile fibers for making garments that are warm even when they are wet. See if your library has any books on textiles and textile fibers. I've got a book I picked up at a rummage sale that is the text for a community college course in textile science, and the description of how synthetic and natural fibers are prepared, spun and woven is very interesting. Developments in the past few decades have made some surprising changes from the straightforward mechanization of techniques that go back for millennia. For example, weft fibers can be spun into thread by air currents as the fabric is woven in sealed looms, and non-woven textiles with a wide range of properties are becoming more common for both traditional and innovative uses.