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New answers tagged surface-tension

3

You're calculating the rate of liquid flow through a tube under a specified pressure gradient. The rate of flow changes depending on whether the flow is laminar or turbulent. Laminar flow is described by the Hagen-Poiseuille equation: $$\Delta P = \frac{8\mu\ell V}{\pi r^4}$$ where $\Delta P$ is the pressure drop, $\mu$ is the viscosity of your saline ...

3

Your fractal pattern will fail for reasons already given. However, given a large enough lake, you should be able to stand on a frame which is supported by a very long (perhaps circular) wire. All you need is for the force per meter (assuming uniformly applied) caused by your body weight and the structure itself to be less than the surface tension force ...

1

The problem lies in your simplistic assumption that the perimeter is the only thing that matters. The actual force can be no greater that the weight of displaced water (see for example a capillary) and as the force you try to exert, so the amount of water displaced will increase. That doesn't mean you could not use surface tension to "walk on water" - just ...

4

Since the force is based on the wetted perimeter, any configuration that would make the perimeter very large in a very small area would be overwhelmed by the surface tension of the water droplets connecting nearby perimeters. So the effective perimeter would be much lower. So you are sunk!

1

As if you will see that a capillary tube kept in a beaker filled with water,so the water level rises but if the length of the capillary tube is insufficient than the angle of cos theta will be of 90 it means that its just impossible,and the surface tension force will be just stopped.

0

The stress-energy tensor that general relativity uses includes a three by three matrix that signifies pressure and stress. It's not clear if you count things that are under tension in one direction and pressure in another as positive or negative pressure, but if the matrix is negative definite, meaning that the object is being pulled apart to some degree in ...

0

Besides negative gauge pressure (that could be defined as tension), there are already a couple of great answers with examples of negative pressures from John Rennie and from Dan. In fundamental physics, in the so-called bag models a negative pressure is also introduced in the stress-energy tensor to preserve Lorentz invariance: the physical meaning is ...

2

Pressure is the (outwardly directed) force normal to any area. This definition most naturally fits hydrostatic pressure, e.g. in gases and liquids. In ideal media, this kind of pressure is never negative. In real media, that is not necessarily true. The most obvious example occurs at the boundary of just about any liquid: There a negative pressure acts on ...

2

The adhesive force between the water molecules and the interior of the cup should... Even in absence of adhesive force, the water will never move in 0-gravity, because there is no up nor down, no force is acting on it. You can clearly see in this video at 1:15 that in order to get the water out of a plastic cup you have to tap it on the bottom

14

If you simply held a cup upside down in zero gravity, the liquid ought not to pour out. However, things in zero gravity still obey Newton's laws. If you pull away the cup, the water ought to stay behind. In reality, a sudden move of the cup would create a lower pressure behind the water than in front so the air pressure would try to keep it in the cup, but ...

3

Remember the laws of Newton. In this case the water will only accelerate with the forces you apply when tilting the cup. Assuming not fierce tilting of the cup: By the hydrogen interactions the water will therefore most like just float around shaped as one or more slightly deform bubbles in mid-air, or inside the cup depending on the "tilting forces".

10

Pour? No such thing without gravity. In NASA TV (see video), I saw the prototype coffee cups. They are shaped with a sharp crease, to allow liquid to ride up the groove. More advanced product would also mix waxy and wettable surfaces to keep it stuck to the inside of the cup but not crawl over the brim, except at the sip line. The pictures are hard to ...

0

The Mie–Gruneisen equation of state for solids http://en.wikipedia.org/wiki/Mie%E2%80%93Gruneisen_equation_of_state is a model that combines the thermal pressure components and "cold" components of the pressure where the latter is derived thermodynamically from a model intermolecular potential. It has the form $p = p_T(\rho_0,T) + p_c(\rho_0,\chi)$, where ...

0

When you rock the espresso from side to side you make the surface larger and stretch the bubbles. When the surface comes back to its original size it is energetically more favorable for the bubbles to bunch (lowering their exposed surface area). Every time you rock the cup, the thinner region is stretched more (relatively) and so the bunches end up ...

-1

All water in liquid form has some surface tension. This inter-molecular attraction can be weakened by the kinetic energy of the water molecules i.e. heat. Thus, you can be heating the water.

3

You can't remove the entire surface tension and still have a surface (without tension the water will just atomise under thermal fluctuations and vaporise). But you can certainly reduce the influence of hydrogen bonds and thus surface tension. Heating up the water is the simplest method - it will drown out the enthalpic contributions of the hydrogen bonds ...

2

You could probably get a negative pressure in polymer physics, so you could view a big block of rubber as behaving this way. Basically: negative pressures happen when an increase in volume causes a decrease in entropy. Polymers might be a good example because you have these molecules which "want" to be tangled up and kinked ("want" in the sense of "it is ...

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