0 Members and 1 Guest are viewing this topic.
The 'C' effect is noticeable when a lock gate between fresh water and sea water is opened. The gates open easily when the forces are equal but fresh water instantly starts to pour out into the sea as soon as they are open because its level is higher. It looks bizarre if you are used to canal locks.
"This experiment, while simple has implications for our own circulatory system."How?Blood etc have pretty near constant density.
When you turn the C: experiment upside down that’s when the density flow becomes really interesting.
QuoteWhen you turn the C: experiment upside down thatís when the density flow becomes really interesting.We have been here before and there is not much point bringing in your 'tension' in water idea. The same forces apply whichever way up the tube may be orientated. That is only 'interesting' in the same way that all hydrostatic effects are interesting. The molecules in any experiment can only behave in the way that they will always behave. They can't 'know' what experiment they're a part of.The medical aspects of posture are popular with the of medicine and there are a lot of people who swear by all sorts of odd therapies. The placebo effect is extremely powerful with certain people and at certain times. That doesn't mean that the effect can be explained in 'quasi mechanical' terms. The explanation is much more likely to be in the psychological direction.
When you turn the C: experiment upside down thatís when the density flow becomes really interesting.
Add a pinch of salt and this diagram comes to life without the need of a pump!
Imagine a narrow tube filled with water and running to the ground from a treetop 360 feet in the air. Water is free to move in the xylem, and the walls of the xylem tube provide no direct support to the water inside. The support comes instead from the water itself. Its internal cohesiveness makes the column of water act like a long suspended string, and the tension on the molecules at any point in the column must support the weight of all the water below them. Expressed as a pressure, or force per unit area, the tension on the water in the xylem is surprisingly high: for every thirty feet of tree height, the tension increases by roughly fifteen pounds per square inch. For a xylem tube 360 feet high, the tension at the top is 180 pounds per square inch.
RDSo are you saying that a liquid is the same as a solid? You imply that water is just like a chain. Inter molecular forces in liquids are her small - enough to produce surface tension, which is a very small effect. You tow your car with a chain and not a column of water. Do you have evidence to the contrary?
tension at the top [of 360 foot tree] is 180 pounds per square inch.
Without muscular activity? A guardsmanís muscles are not relaxed. The pressure on the base of the foot is compromising the circulation. This is why they shift their weight from one foot to another to relieve the pressure and assist the circulation to get past the obstructed vessels.Airline passengers compromise their circulation by sitting in one position for too long, often falling asleep for hours on end,
If you had a tube of water with two freely moving, (and snugly fitting) pistons, you could tow your car with it if it had a diameter of about three inches.
QuoteIf you had a tube of water with two freely moving, (and snugly fitting) pistons, you could tow your car with it if it had a diameter of about three inches. That has been explained in terms of atmospheric pressure by Otto von Guericke years ago. See this link among many others....sorry, you cannot view external links. To see them, please
REGISTER or LOGIN
this glass-sheet demonstration would work in a vacuum.
Quotethis glass-sheet demonstration would work in a vacuum.That, again, is merely a statement. Have you any evidence of this.
Cohesion (n. lat. cohaerere "stick or stay together") or cohesive attraction or cohesive force is a physical property of a substance, caused by the intermolecular attraction between like-molecules within a body or substance that acts to unite them. Water, for example, is strongly cohesive as each molecule may make four hydrogen bonds to other water molecules in a tetrahedral configuration. This results in a relatively strong Coulomb force between molecules.
What value do these inter molecular forces have, btw? Can you quote a value from somewhere. You imply that it has been measured. It would have huge implications on things like the boiling point of water, for instance.
Quotethis glass-sheet demonstration would work in a vacuum.That, again, is merely a statement. Have you any evidence of this.You might bear in mind that the force which has been measured can be explained by atmospheric pressure.What value do these inter molecular forces have, btw? Can you quote a value from somewhere. You imply that it has been measured. It would have huge implications on things like the boiling point of water, for instance.
The value has been measured- it's about 2.5KJ/g
The strong intermolecular forces between (polar) water molecules are why water has higher boiling point than similar sized molecules, e.g. water (H20) is liquid at room temperature, whereas ammonia (NH3) and methane (CH4) are gases at room temperature.Hydrogen cyanide (HCN) boils at 26oC.
That's fair enough. I was trying to relate it to a possible 'tensile strength' so the number would be handy. I don't think that pressure vs boiling point is irrelevant. Doesn't it relate to the energy needed to make a surface molecule break free? If there is even a hint of a surface anywhere within the liquid bulk then it can form a bubble at a low enough pressure and any tension you might have had will not count. This argument would not prohibit dynamic tension, as long as the load is applied briefly enough.But, if a normal lift pump will not operate over a greater height than that which corresponds to atmospheric pressure for the liquid density, then how can an inverted u tube support a greater head?I appreciate that, in a small bore tube, the effects of the tube surface could make a difference but, in a bulk liquid, what can keep a column above that which is supported by the AP difference?The paper quoted above agrees with my point - it doesn't work for static pressures below the saturated vapour pressure.
I wish you could tell me the difference between the top of a U tube and the top of a single tube...