question: Why does the liquid stay in the straw when you cover the top with your finger?
comment: Because the liquid moving away from your finger creates a vacuum between the two. When yoi move your finger away the vacuum is broken and the liquid is free to move.
passages: To demonstrate, the longer lower leg of a common siphon can be plugged at the bottom and filled almost to the crest with liquid as in the figure, leaving the top and the shorter upper leg completely dry and containing only air. When the plug is removed and the liquid in the longer lower leg is allowed to fall, the liquid in the upper reservoir will then typically sweep the air bubble down and out of the tube. The apparatus will then continue to operate as a normal siphon. As there is no contact between the liquid on either side of the siphon at the beginning of this experiment, there can be no cohesion between the liquid molecules to pull the liquid over the rise. It has been suggested by advocates of the liquid tensile strength theory, that the air start siphon only demonstrates the effect as the siphon starts, but that the situation changes after the bubble is swept out and the siphon achieves steady flow. But a similar effect can be seen in the flying-droplet siphon (see above). The flying-droplet siphon works continuously without liquid tensile strength pulling the liquid up.
   All of this careful settling of the "yerba" ensures that each sip contains as little particulate matter as possible, creating a smooth-running mate. The finest particles will then be as distant as possible from the filtering end of the straw. With each draw, the smaller particles would inevitably move toward the straw, but the larger particles and stems filter much of this out. A sloped arrangement provides consistent concentration and flavor with each filling of the mate.
   Again in 2011, Richert and Binder (at the University of Hawaii) examined the siphon and concluded that molecular cohesion is not required for the operation of a siphon but relies upon gravity and a pressure differential, writing: "As the fluid initially primed on the long leg of the siphon rushes down due to gravity, it leaves behind a partial vacuum that allows pressure on the entrance point of the higher container to push fluid up the leg on that side".
   BULLET::::- Loop of Henle Descending: The liquid passes from the thin descending limb to the thick ascending limb. Water is constantly released via osmosis. Gradually there is a buildup of osmotic concentration, until 1200 mOsm is reached at the loop tip, but the difference across the membrane is kept small and constant.
   Apply Bernoulli's equation to the surface of the upper reservoir. The surface is technically falling as the upper reservoir is being drained. However, for this example we will assume the reservoir to be infinite and the velocity of the surface may be set to zero. Furthermore, the pressure at both the surface and the exit point C is atmospheric pressure. Thus:
  
  Apply Bernoulli's equation to point A at the start of the siphon tube in the upper reservoir where "P" = "P", "v" = "v" and "y" = −"d"
   Some workers restrict their definition of the capillary fringe only to the tension-saturated base portion and exclude it wholly from the vadose zone. 
   The father and son researchers, Ramette and Ramette, successfully siphoned carbon dioxide under air pressure in 2011 and concluded that molecular cohesion is not required for the operation of a siphon but that: "The basic explanation of siphon action is that, once the tube is filled, the flow is initiated by the greater pull of gravity on the fluid on the longer side compared with that on the short side. This creates a pressure drop throughout the siphon tube, in the same sense that 'sucking' on a straw reduces the pressure along its length all the way to the intake point. The ambient atmospheric pressure at the intake point responds to the reduced pressure by forcing the fluid upwards, sustaining the flow, just as in a steadily sucked straw in a milkshake."
   The primary force that creates the capillary action movement of water upwards in plants is the adhesion between the water and the surface of the xylem conduits. Capillary action provides the force that establishes an equilibrium configuration, balancing gravity. When transpiration removes water at the top, the flow is needed to return to the equilibrium.
   Now the mate is ready to receive the straw. Wetting the "yerba" by gently pouring cool water into the empty space within the gourd until the water nearly reaches the top, and then allowing it to be absorbed into the "yerba" before adding the straw, allows the preparer to carefully shape and "pack" the "yerba"'s slope with the straw's filtering end, which makes the overall form of the "yerba" within the gourd more resilient and solid. Dry "yerba", though, allows a cleaner and easier insertion of the straw, but care must be taken so as not to overly disturb the arrangement of the "yerba". Such a decision is entirely a personal or cultural preference. The straw is inserted with one's thumb on the upper end of the gourd, at an angle roughly perpendicular to the slope of the "yerba", so that its filtering end travels into the deepest part of the "yerba" and comes to rest near or against the opposite wall of the gourd. It is important for the thumb to form a seal over the end of the straw when it is being inserted, or the negative pressure produced will draw in undesirable particulates.
   The balance of these forces varies with change in temperature or solvent properties. The total osmotic pressure acting on the system is the sum osmotic pressure of the gel. It is further shown that the phase transition can be induced by the application of an electric field across the gel. The volume change at the transition point is either discrete (as in a first-order Ehrenfest transition) or continuous (second order Ehrenfest analogy), depending on the degree of ionization of the gel and on the solvent composition.
  
  Section::::Structural relaxation.:Elastic continuum.
   Internal water pulses from the straw (into the drop) and air movement around the suspended solution drop, can cause the rafts to spin swiftly around the drop surface. If there is almost no air movement around the suspended drop, then after approximately 12 minutes or more, the micro rafts may join up and form a latticework, which covers the entire drop surface. If the solution drop hangs too long on the straw (≈ 30 minutes), it may completely calcify over and block the calthemite straw tip.
  
  Section::::External links.
  
  BULLET::::- Lubbock Area Grotto Calcite (Inventory)/Raft Accessed 2012-06-23.
  
  BULLET::::- Karstbase—Calcite raft
   Similar to a gravity bong, a waterfall bong utilizes both a bottle and a cap or screen rigged over the bottle's mouth to hold cannabis. In this case, however, the bottle—which has one or several holes drilled near or at the bottom—is either filled with water or placed in a larger container filled with water before the cannabis is packed. The holes are then uncovered, or the bottle is simply raised from the container, evacuating the water either onto the ground or back into the container. When heat is applied to the drug, the resultant smoke is forced into the bottle with negative gauge pressure, as with the gravity bong. Once the water is evacuated, the smoke can be inhaled from the bottle. Variations on this concept are also used.
   There are two leading theories about how siphons cause liquid to flow uphill, against gravity, without being pumped, and powered only by gravity. The traditional theory for centuries was that gravity pulling the liquid down on the exit side of the siphon resulted in reduced pressure at the top of the siphon. Then atmospheric pressure was able to push the liquid from the upper reservoir, up into the reduced pressure at the top of the siphon, like in a barometer or drinking straw, and then over. However, it has been demonstrated that siphons can operate in a vacuum and to heights exceeding the barometric height of the liquid. Consequently, the cohesion tension theory of siphon operation has been advocated, where the liquid is pulled over the siphon in a way similar to the chain model. It need not be one theory or the other that is correct, but rather both theories may be correct in different circumstances of ambient pressure. The atmospheric pressure with gravity theory obviously cannot explain siphons in vacuum, where there is no significant atmospheric pressure. But the cohesion tension with gravity theory cannot explain CO gas siphons, siphons working despite bubbles, and the flying droplet siphon, where gases do not exert significant pulling forces, and liquids not in contact cannot exert a cohesive tension force.
   Though on the face of it connecting a packet capture appliance via a SPAN port appears to make it more secure, the packet capture appliance would ultimately still have to be connected to the network in order to allow management and data retrieval. Though not accessible via the SPAN link, the appliance would be accessible via the management link.
   A basic spring-loaded pin consists of 3 main parts: a "plunger", "barrel", and "spring". When force is applied to the pin, the spring is compressed and the plunger moves inside the barrel. The shape of the barrel retains the plunger, stopping the spring from pushing it out when the pin is not locked in place.
   This is the traditional approach, in which the pressure increases continuously at a constant rate (figure 1), which can be modified depending the instrument and the user's requirements, and the gas flow through the sample is measured. Again, the number of data points acquired can be adjusted by the user.
   A practical application of capillary action is the capillary action siphon. Instead of utilizing a hollow tube (as in most siphons), this device consists of a length of cord made of a fibrous material (cotton cord or string works well). After saturating the cord with water, one (weighted) end is placed in a reservoir full of water, and the other end placed in a receiving vessel. Note that the reservoir must be higher than the receiving vessel. Due to capillary action and gravity, water will slowly transfer from the reservoir to the receiving vessel. This simple device can be used to water houseplants when nobody is home.
   Another common misconception about siphons is that because the atmospheric pressure is virtually identical at the entrance and exit, the atmospheric pressure cancels, and therefore atmospheric pressure can't be pushing the liquid up the siphon. But equal and opposite forces may not completely cancel if there is an intervening force that counters some or all of one of the forces. In the siphon, the atmospheric pressure at the entrance and exit are both lessened by the force of gravity pulling down the liquid in each tube, but the pressure on the down side is lessened more by the taller column of liquid on the down side. In effect, the atmospheric pressure coming up the down side doesn't entirely "make it" to the top to cancel all of the atmospheric pressure pushing up the up side. This effect can be seen more easily in the example of two carts being pushed up opposite sides of a hill. As shown in the diagram, even though the person on the left seems to have his push canceled entirely by the equal and opposite push from the person on the right, the person on the left's seemingly canceled push is still the source of the force to push the left cart up.
   1) Indirectly - by measuring the distance the water level drops in the graduated tube over a measured length of time. It is assumed that this is due to the cutting taking in water which in turn is necessary to replace an equal volume of water lost by transpiration.
  
  2) Directly - by measuring the reduction in mass of the potometer over a period of time. Here it is assumed that any loss in mass is due to transpiration.
   BULLET::::- A "crazy (or "krazy") straw" is hard, transparent or translucent plastic and has a number of twists and turns at the top. When liquid is sucked through the straw, it quickly flows through the winding path, creating a mildly amusing spectacle, popular with children. The crazy straw may have some therapeutic benefit for people with autism. The crazy straw was invented by Arthur Philip Gildersleeve and patented in 1936.
  
  BULLET::::- Extendo-straws come in small plastic wrappings like miniature straws, but can extend to reach the bottom of the carton.
   Cassie and Baxter found that if the liquid is suspended on the tops of microstructures, "θ" will change to "θ":
  
  where φ is the area fraction of the solid that touches the liquid. Liquid in the Cassie–Baxter state is more mobile than in the Wenzel state.
   The siphon in the video demonstration operated steadily for more than 28 minutes until the upper reservoir was empty. Another simple demonstration that liquid tensile strength isn't needed in the siphon is to simply introduce a bubble into the siphon during operation. The bubble can be large enough to entirely disconnect the liquids in the tube before and after the bubble, defeating any liquid tensile strength, and yet if the bubble isn't too big, the siphon will continue to operate with little change as it sweeps the bubble out.
   In more detail, one can look at how the hydrostatic pressure varies through a static siphon, considering in turn the vertical tube from the top reservoir, the vertical tube from the bottom reservoir, and the horizontal tube connecting them (assuming a U-shape). At liquid level in the top reservoir, the liquid is under atmospheric pressure, and as one goes up the siphon, the hydrostatic pressure decreases (under vertical pressure variation), since the weight of atmospheric pressure pushing the water up is counterbalanced by the column of water in the siphon pushing down (until one reaches the maximal height of a barometer/siphon, at which point the liquid cannot be pushed higher) – the hydrostatic pressure at the top of the tube is then lower than atmospheric pressure by an amount proportional to the height of the tube. Doing the same analysis on the tube rising from the lower reservoir yields the pressure at the top of that (vertical) tube; this pressure is lower because the tube is longer (there is more water pushing down), and requires that the lower reservoir is lower than the upper reservoir, or more generally that the discharge outlet simply be lower than the surface of the upper reservoir. Considering now the horizontal tube connecting them, one sees that the pressure at the top of the tube from the top reservoir is higher (since less water is being lifted), while the pressure at the top of the tube from the bottom reservoir is lower (since more water is being lifted), and since liquids move from high pressure to low pressure, the liquid flows across the horizontal tube from the top basin to the bottom basin. Note that the liquid is under positive pressure (compression) throughout the tube, not tension.
   Section::::Kelvin equation.:Dependence on contact angle.
   While if both ends of a siphon are at atmospheric pressure, liquid flows from high to low, if the bottom end of a siphon is pressurized, liquid can flow from low to high. If pressure is removed from the bottom end, the liquid flow will reverse, illustrating that it is pressure driving the siphon. An everyday illustration of this is the siphon coffee brewer, which works as follows (designs vary; this is a standard design, omitting coffee grounds):
  
  BULLET::::- a glass vessel is filled with water, then corked (so air-tight) with a siphon sticking vertically upwards
  