0 Members and 1 Guest are viewing this topic.
quote:Yes even if its on top of something else! Take a look at the flow of dense rock pulled towards the Earths core
quote:To state that solutes and sugars stay put and are not acted upon by gravity is absurd! How do we tap rubber, harvest amber and maple syrup??? There is an obvious downward flow!!!!
quote:And for every action there must be a reaction !!!!!
quote:"The explanation requiring the fewest assumptions is most likely to be correct."
quote:Originally posted by rosyIf the primary system for moving water up trees is this convection type system you're proposing, how do the sugars get *up* the trees to the ends of the branches for leaf formation in the spring? According to your model, if there aren't any leaves yet how does the flow get started and worse how does it draw more sugars (and amino acids and whatever else it needs) up than it drops down (which it must in order to construct new leaves)? It's got to use active transport in the phloem.
quote:sugar is produced and water is lost by evaporation from the leaves.Sugars are transferred by (mainly passive) transport (depending on the concentrations) into the phloem. Given the sugars are already (since they're made in the leaves and moved to other parts of the plant) moving down a concentration gradient, there is no reason for more water to follow them across the cell.
quote:Loss of water from the leaves results in water being drawn up from the roots via the xylae(osmosis).
quote:The sugars want to move to a position of lower energy/higher entropy (and so to places where there is less sugar already). There *is* an energy gain in going downwards, yes, but as Dave points out it isn't actually very big if you're losing a whole load of water at the top. Your Brixham experiment depends on using the weight of the water coming over the top of the loop to draw the water below it up. In order to produce any energy at all the salt/sugar solution has actually to move
quote:, which in your model it can't do unless the water which it pulls up follows it straight back down the opposite tube. Indeed, as was pointed out by EL Hemetis, there is before us the evidence of plants quite happily growing with their leaves below their roots. I'm far more convinced by the idea that that concentration effects dominate.
quote:Amber really is just the fossilized stuff. The "amber" people harvest is probably copal, which I *think* is a form of resin.http://www.emporia.edu/earthsci/amber/copal.htm[/quote]Ok I will concede that it may not be true amber in the sense of fossilized resin, but the stuff did come from a tree all said and done [:I]Andrew"The explanation requiring the fewest assumptions is most likely to be correct."K.I.S. "Keep it simple!"
quote:Absolute nonsense, osmosis requires the belief that water can attract water up a tree and out through the leaves? I cannot see any logic in your argument here.
quote:Firstly, it is not a convection system. It is a flow and return system which operates when concentrations of denser solutes occur above less dense solutes due to evaporation.
quote:In the spring, there is an initial temperature change, which initiates the flow and return system, causing the circulation inside the leafless tree to flow, and to generate both positive and negative pressures within the moving fluids as it goes.
quote:Actually there is a very good reason for more water to follow, that being the cohesiveness of water molecules adhering to water molecules. This is precisely why I keep asking you to repeat the experiments.
quote:Sorry, I disagree with you, the weight of the water in the opposing side is irrelevant
quote:The coloured solution will flow in the opposite side to the siphon, and can be clearly seen in the turbulence of the coloured solution as it interacts with the clean solution.
quote:But somewhere within the plant or tree, there is a pathway for gravity to draw solutes down
quote:This flow system will always run in the path of least resistance, be it horizontal, down or up, it makes no difference. But somewhere within the plant or tree, there is a pathway for gravity to draw solutes down,
quote:Originally posted by daveshortsquote:Absolute nonsense, osmosis requires the belief that water can attract water up a tree and out through the leaves? I cannot see any logic in your argument here.You may find this stuff interesting about osmosishttp://www.chaosscience.org.uk/pub/public_html//article.php?story=20050301222247333and http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/ospcal.htmlhas a nice program for calculating osmotic pressuresIf evaporation keeps the concentration of the liquids in teh leaf hight, osmosis can generate the appropriate pressures to suck water out of the xylem, and the column of water in the xylem behaves like a wire (because it is cohesive) so if you pull at the top the whole column moves up, it all sounds consitent to me...
_____ <- membrane | | | | | | | | <- code | | |__| |__| | | | | <-resivoir |_________|
quote:Originally posted by daveshortsin the diagram where i wrote code I meant tube... I think I need to eat supper
_________ __ / ___ \ | | | / \ | | | | | | | | | | | | | | | | | | | | | |__| |__| |__| | | | | | |
|__________| |__________| <- concentrated solution | | | | | | | | .......... | | | | |__| |__| | | | | <- water |________|
quote:Rosy, the concentrated sap in the phloem that is not actually taken up by the trees increasing growth cycle, is rediluted by incoming water from the soil, under a negative pressure generated by the falling sap.
quote:As the Brixham experiment demonstrates, it is possible to raise the water in excess of 14 metres, but eventually the water bead will break. When I say a siphon will not work, it is because I have actually tested it!
quote:When me and Rosy are talking about negative pressure, we mean negative absolute pressure - where a vacuum is zero pressure.
quote:The reason why GCSE textbooks tell you that a syphon will not work above 33 feet is that atmospheric pressure is enough to lift water 33feet, so up to this point the water is under compression by the atmospheric pressure. If you go above 33feet the water is in tension (a negative pressure) and should therefore boil or cavitate or something breaking the syphon.
quote:Now as you have found out real life is rarely as simple as GCSE textbooks, and water can actually survive a negative pressure if it is continuous, there are minimal dissolved gasses (which you removed by boiling) because of the cohesiveness of the water. It is not stable like this and a small bubble will cause it to cavitate. However if there are no gasses this is unlikely enough for you to do your experiment in Brixham.
quote:Now if you are using the same liquid in both tubes the pressure in the tube is only dependent on how much weight there is pulling on it, and the chance of cavitation is just dependent on the pressure. So the only difference between a normal syphon and your syphon is that the extra weight is provided by an extra length of water rather than salt.
quote:What would you expect to happen to the water levels in the tube, when you remove the both ends of the tube from the bottles, while it remains suspended above the 33 feet limit?
quote:Originally posted by l_kryptoniteOr you could get involved in the incredibly complex discussion being held in the general science section. I need to do about 3 years of study before I get back into that one though. Way out of my league.
quote:Your tube is pretty rigid, but if you squeeze it really hard I expect it will deform a little bit, you would only need a 5-10 percent deformation to cause a .5m movement in the water. Are you using the flexible clear PVC tube or the translucent white much more ridgid stuff?
quote:Hang on a minute - do I understand you correctly in that the bottom half metre of the tube empties and is full of air, and then stops?
quote:Have you done anything else other than removed the demijohn? because just removing the demijohn will not alter the pressures at all - so you haven't done anything to the water column apart from let water fall out of the bottom,
quote: eg you shouldn't have altered the tension in the elastic band (whether the elasticity is due to water stretching or the tube deforming) as you haven't changed the size of the weights on each end... did you pull the ends out of the demi-johns by lifting the whole apparatus or just the ends of the tubes?
quote:ps. by the way my calculation above was considering the force from the whole earth on the hydrogen atoms in a water molecule. Perhaps I should have said that on a molecular scale the earth's gravity is a very small force.
quote:Yes, it’s the rigid translucent stuff! The softer walled tube will simply neck )( under the negative tension. This rigid stuff does not neck and therefore the diameter internally will not reduce as a result of the negative tension. If I were able to squeeze it and alter its shape, it still would not alter the volume, as in order to do this one would have to compress the tube equally from all directions and this would take a huge force.
quote:Just the ends of the tubes!Not quite correct Dave, there has been a reduction in the weights, because the water in the two bottles has been disconected, and thes do have considerable weight. Consider the water in the bottles as part of the mass of water inside the tubes and you begin to understand how trees draw water and mineral from the surounding soil into their roots, or into a cut stem or trunk, with no roots.
quote:I think you still might be wrong with this way of looking at gravity. Try thinking of gravity as being a huge force capable of holding everything in homeostasis.
quote:Did you lift the tubes up or down when you removed the tubes?
quote:So if you pull the tube out of the bottle, unless the level of the end of the tube is different to the level of the water in the bottle nothing has changed.Did you lift the tubes up or down when you removed the tubes?
quote:I am not sure what you mean by homeostasis, as it is not in the oed and the only definition I can find is that it is a biological system that is stable due to negative feedback. Some systems acting under gravity are stable due to negative feedback - eg water in a glass is stable, but to say everything acting under gravity is under negative feedback is ridiculous - there is no way that a cricket ball in the air is going to be held in position... I am confused by what you mean.[/quote][/quote]ho·me·o·sta·sis (hm--stss)n. The ability or tendency of an organism or a cell to maintain internal equilibrium by adjusting its physiological processes. The processes used to maintain such bodily equilibrium.fits ok with this paradigm and discussion on trees and plants?Your cricket ball is in the air, because gravity holds the atmosphere in place, and it will eventually come back to earth and its ultimate resting place, due to the inevitable effects of gravity, no matter how hard you throw it. Just like a nuclear explosion is brought back under control by gravity"The explanation requiring the fewest assumptions is most likely to be correct."K.I.S. "Keep it simple!"
quote:Sorry, I did not make myself clear about the requirement of compressing the whole tube equally. I was relating to the negative water causing the tube to collapse equally, as this would be the case with a liquid under tension. Not at all like a finger and thumb compressing it.
quote:ho·me·o·sta·sis (hm--stss)n. The ability or tendency of an organism or a cell to maintain internal equilibrium by adjusting its physiological processes. The processes used to maintain such bodily equilibrium.fits ok with this paradigm and discussion on trees and plants?
quote:But to hide this thread from the view of people who are interested in physics and fluid dynamics is nothing short of censorship at best!
quote:Originally posted by daveshortsAndrew With physics it is always a good idea to keep an eye on where the energy is going, So just answer me this...98% of the water that goes up the tree is evaporated, so for every 100kg of water going up the tree at the most 2kg of water comes back down.lifting 100kg of water 100m takes 10 000Jdropping 3kg of water and sugar 100m releases 300Jwhere does the other 9700J come from?