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Reply to anut:
Yes, I agree, and never said otherwise.
Here again I am in agreement. Capillary action is simply the drawing of water into a tube or a porous material.
Yes, surface tension is dependent upon temperature, and diminishes with heating. I agree. Here's where we disagree:
Capillary action does not occur simply due to surface tension. Surface tension is just one of the forces used in capillary action. The other forces at work are noted in your quote of my post. The strength of surface tension determines the cohesive force of the water (its own attraction to itself). Water has a rather strong cohesive bond, and this is what causes a drop of water to form a spherical shape. When water is placed in a tube, the surface tension is not only relative to the liquid/air interface, but also to the interface between the water and the walls of the container. The surface tension of the water/air interface is greater than the water/walls interface, and in the area where the interfaces meet, the geometry is determined by the balancing of these forces. A water/air/glass tube interfacing causes the concave meniscus effect that I mentioned previously, and provides a contact angle, at the wall, of less than 90 degrees. Since the water is higher at the contact area with the wall it wets the wall. The degree of wetting relies on the contact angle. But what causes the water level to continue to rise in a capillary tube, beyond the meniscus curvature? If none of the properties is changed, then the curvature and resultant contact angle will remain the same. Wetting is what overcomes the force of gravity, and this is easier to accomplish when the inside diameter of the tube is made smaller, since the same column height of the water will have less gravitational accelleration force exerted upon it. Now let's say that water will rise X inches inside a capillary tube. Does that mean that if we cut the top of the tube off, at a height below X inches, that water will continue to rise and overflow at the top of the tube? No, and the reason why it can't do this is because there is no longer any wetting action. Therefore, wetting action is the property that allows capillary action to take place in a tube. Wetting works even better in a porous material, such as a sponge or paper towel, because of the absorbent quality of the material, and that's why a wick of such porous material, when inserted into water at the top of a capillary tube, allows the water to be lifted above the tube. A wick of high absorbent quality, which allows better wetting, can lift the water considerably higher than the height of the water within the capillary tube. To demonstrate the ability of an absorbent material to lift water, just place two or three inches of water in your kitchen sink and insert the end of a towel into the water, and to the bottom of the sink. Place the remainder of the towel at countertop level. The towel will draw water upwards several more inches to the countertop level. If you drape the towel down over the front facing edge of the countertop, the water will start dripping onto your floor, and will continue to do so until all the water is emptied from the sink. If you place the end of the draped towel into a partially filled container of water where the water level is lower than that of the water in the sink, the water will continue to drain from the sink and to fill the container. It's the same wicking principles used in the smaller scale experiments that I suggested, which used drinking glasses. You can go big or you can go small, but the end results will be the same. So try it, you may like it.
I believe that my description of the three experiments is complete enough that you should be able to visualize and duplicate them without need of a diagram. If you need a diagram, then you draw one. I have other things to do. Go ahead and perform the experiments as I stated them, and let me know if your results are different. Simple as that. Why do you think the experiment needs to be insulated from the ambient (room, or container, temperature)? Dave's device is a container in which everything inside it is at ambient temperature. Try the experiment with the glasses, the water in the glasses, the surrounding air, and the paper towel wick, all stabilized at room temperature, and your result will still be the same as the results that I mentioned.
Yes, by all means let's do that. I'll stick by anything that I have said in this thread as being correct, and in alignment with scientific facts. You can continue to disagree if you choose to, but I think enough has already been said, and I refuse to be drawn into a protracted argument. Please don't take offense at that, as none is intended.
I wish you well,
Rick
Originally posted by anut
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Wicking IS capillary action. The term wicking usually refers to the movement of moisture within a wicking fabric by capillary action. In the "perpetual motion" experiment, the capillary action is not just limited to the glass tube.
Capillary action is obviously due to the solution's surface tension, which in turn depends on the temperature.
Capillary action does not occur simply due to surface tension. Surface tension is just one of the forces used in capillary action. The other forces at work are noted in your quote of my post. The strength of surface tension determines the cohesive force of the water (its own attraction to itself). Water has a rather strong cohesive bond, and this is what causes a drop of water to form a spherical shape. When water is placed in a tube, the surface tension is not only relative to the liquid/air interface, but also to the interface between the water and the walls of the container. The surface tension of the water/air interface is greater than the water/walls interface, and in the area where the interfaces meet, the geometry is determined by the balancing of these forces. A water/air/glass tube interfacing causes the concave meniscus effect that I mentioned previously, and provides a contact angle, at the wall, of less than 90 degrees. Since the water is higher at the contact area with the wall it wets the wall. The degree of wetting relies on the contact angle. But what causes the water level to continue to rise in a capillary tube, beyond the meniscus curvature? If none of the properties is changed, then the curvature and resultant contact angle will remain the same. Wetting is what overcomes the force of gravity, and this is easier to accomplish when the inside diameter of the tube is made smaller, since the same column height of the water will have less gravitational accelleration force exerted upon it. Now let's say that water will rise X inches inside a capillary tube. Does that mean that if we cut the top of the tube off, at a height below X inches, that water will continue to rise and overflow at the top of the tube? No, and the reason why it can't do this is because there is no longer any wetting action. Therefore, wetting action is the property that allows capillary action to take place in a tube. Wetting works even better in a porous material, such as a sponge or paper towel, because of the absorbent quality of the material, and that's why a wick of such porous material, when inserted into water at the top of a capillary tube, allows the water to be lifted above the tube. A wick of high absorbent quality, which allows better wetting, can lift the water considerably higher than the height of the water within the capillary tube. To demonstrate the ability of an absorbent material to lift water, just place two or three inches of water in your kitchen sink and insert the end of a towel into the water, and to the bottom of the sink. Place the remainder of the towel at countertop level. The towel will draw water upwards several more inches to the countertop level. If you drape the towel down over the front facing edge of the countertop, the water will start dripping onto your floor, and will continue to do so until all the water is emptied from the sink. If you place the end of the draped towel into a partially filled container of water where the water level is lower than that of the water in the sink, the water will continue to drain from the sink and to fill the container. It's the same wicking principles used in the smaller scale experiments that I suggested, which used drinking glasses. You can go big or you can go small, but the end results will be the same. So try it, you may like it.
Regarding your experiment, please post a diagram of your setup. This will give us an opportunity to understand how well the experimental setup is insulated from the ambient.
So, please focus on the scientific facts ONLY.
I wish you well,
Rick
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