13
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Accepted
Does capillary rise violate hydrostatic paradox?
The pressures at A and B are indeed equal. However, the pressure in the fluid immediately below the curved meniscus is equal to $p_{atm}-hdg$ as a result of surface tension. So the pressure at A is $...
- 28.4k
12
votes
How is it possible for tall trees to pull water to heights more than 10m?
It's not only atmospheric pressure which is involved in water delivery to a tree, but mainly the capillary action and osmosis.
Osmosis and Hydrostatic Pressure
Roots take advantage of "pressures&...
- 2,069
6
votes
Accepted
Size of a glass capillary for noticable capillary action
It all depends on what you consider "noticeable". The change in height in a capillary comes about from the curvature of the liquid, and the resulting change in pressure.
Simplifying for a moment, the ...
- 117k
5
votes
Accepted
Will a drop of liquid flow from from the wide opening to the narrow opening of a thin funnel by the effect of air pressure?
For the case that you have drawn, the behavior of the drop is actually the exact opposite of what you mention: it will move from right to left.
This is caused by surface tension and the curvature of ...
- 2,799
5
votes
Why doesn't this capillary action generator work?
As you've indicated in your title, the correct question is "why doesn't this work". The system, as described would continue to produce energy indefinitely without any being added to it (perpetual ...
- 673
5
votes
Does folding a paper towel help dry your hands faster by creating interstitial forces?
The speaker actually claims it works by "interstitial suspension". I think he is referring to capillary action, which you are aware is involved here. He does not claim this method is faster, only that ...
- 26.5k
5
votes
Accepted
How fast does liquid rise in a capillary tube?
The equation you have derived is essentially the Lucas-Washburn-Rideal equation which is given by
\begin{equation}
\rho \pi R^2 \dfrac{d}{dt}\left( h \dfrac{dh}{dt} \right) = 2\pi R \sigma \cos(\theta)...
- 627
5
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Does capillary rise violate hydrostatic paradox?
$p_A$ is equal to $p_B$ here. The disparity is arising due to the fact that pressure just outside the meniscus is greater than the pressure inside. This is due to the curvature of the meniscus and ...
- 95
5
votes
Height of fluid and pressure
No, it will not increase, because the adhesive force eliminates the increased gravitational force of water in the column.
- 2,069
4
votes
Accepted
Why don't we include the adhesive and cohesive force while calculating rise in a capillary tube?
Adhesive forces are accounted for when calculating capillary height.
My guess is that you think they are not because you read, somewhere, a discussion in which adhesive forces were used to calculate ...
- 51.5k
4
votes
Capillary tube of insufficient length
The equation for capillary rise can be represented as
$$h=\frac{2T}{rρg}\cosθ$$
if the height of the capillary tube is less than the height calculated by this equation,the water comes up to the ...
- 41
4
votes
Forces causing capillary rise
I would explain it this way:
Adhesion happens because of intermolecular forces of attraction. For example, Water molecules of any aqueous solution contain 2 hydrogen and one oxygen atoms that are ...
- 102
4
votes
Forces causing capillary rise
Surface tension is a phenomenon which occurs irrespective of whether a solid surface is in the vicinity. It is the result of the discontinuity in molecular attractive forces present at the free ...
- 28.4k
4
votes
Accepted
Bent capillary tube
Even though capillary forces may be the dominant force in this situation, hydrostatic (gravitational body) forces are still there. And that results in the equilibrium seen in the left most figure as ...
- 11.3k
4
votes
Accepted
In derivation of capillary rise we take the upwards pressure as $2T/r$. How?
The derivation can be thought of as this:
Let,
Radius of Capillary be $r$
Density of the liquid $\rho$
Height of the liquid be $h$
Surface Tension of Liquid be $T$
Contact angle $\theta$
Weight of ...
- 315
4
votes
Doubt in capillary rise
Surface tension produces a pressure difference across the curved interface between the liquid and the air and it is this difference in pressure which results in the capillary rise.
The pressure is ...
- 79.7k
4
votes
Accepted
Laplace pressure
Think of a balloon.
The surface of the balloon has some tension which wants to make the balloon smaller. This surface tension necessarily means that the pressure inside the balloon is larger than the ...
- 35.1k
3
votes
Accepted
How is sweating a pipe an example of capillary action?
Molten solder has a low contact angle on (clean) copper. So if you looked at a cross section of the pipe joint as the solder was flowing in you'd see something like:
The solder is drawn into the ...
- 334k
3
votes
How is sweating a pipe an example of capillary action?
When you were sweating the pipes, the solder was not only flowing with gravity. It was also being drawn sideways, up, and around to fill the very small gap between the pipe and the fitting. This is ...
- 708
3
votes
How is sweating a pipe an example of capillary action?
The basis for capillary action is attraction between the liquid and the solid, based upon intermolecular or interatomic forces.
When the liquid needs to rise against gravity to increase wetted ...
- 16k
3
votes
Accepted
"Troll physics": What is wrong with this perpetual machine?
I suggest you build one in your kitchen. Cut a sponge into a J shape and hook it over a pencil, so that the straight edge dangles into a bowl of water. Put piece of tissue paper under the hook to ...
rob♦
- 74.3k
3
votes
Forces causing capillary rise
Brief:
The force you are referring to is exerted on the liquid surface by the solid wall surface it is in contact with. It is a consequence of surface tension in the liquid.
Elaborate:
The liquid ...
- 131
3
votes
Accepted
Contact Angle In Capillary
Yes, the contact angle will change. When the length of the capillary tube is sufficient, we balance the hydrostatic and the capillary pressure to obtain the rise in height $h=\frac{2\gamma\cos\theta}{\...
3
votes
Accepted
Capillary Perpetual Motion
The answer is quite simple.
At the enlarged diameter of the capillary tube, the capillarity is lost/reduced, depending on the diameter. The water will no longer rise into the larger diameter at the ...
3
votes
Accepted
Why does water hold up between the teeth of my comb?
I believe that the force that is keeping those water droplets stationery even when the comb is vertical is the cohesion and adhesion of water molecules as they are attracted to each other (molecules ...
- 2,841
3
votes
Capillary length and Bond number confusion
I think you may be confusing the characteristic (capillary) length with the height of the liquid at the surface (the capillary rise). If $L$ is the characteristic length of the surface of the liquid, ...
- 61
3
votes
Accepted
Why does solder wick absorb solder?
Yes, that is the general principle behind wicks (not just soldiering wicks).
A definition of wick that applies here would be:
Any piece of porous material that conveys liquid by capillary action, ...
- 14.8k
3
votes
Does capillary action affect the accuracy of mercury barometer?
Of course the surface tension affects the height. I wonder why this is never or seldom mentioned in the articles.
The effect applies in both the cistern and the tube but is most significant in the ...
- 31
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