Questions tagged [surface-tension]

Surface tension occurs due to the tendency of liquid molecules to favor their own kind. Surface tension is important in fluid multiphase systems typically at small length and velocity

When to use

This tag should be used for fluid dynamics and statics, if surface tension will play a significant role in the physical process of interest. This significance can be roughly determined by looking at the following two dimensionless numbers:

The Weber number: $We=\frac{\rho u^2 L}{\gamma}$ which signals the relative importance with respect to inertial forces

The Capillary number: $Ca=\frac{\\mu u}{\gamma}$ which signals the relative importance with respect to viscous forces

When both numbers are small, surface tension will be dominant in the system.

Translated this means that the tag should be used for: fluid-fluid systems at small scales ($\mu$m to cm) and small velocities (typically $<1$ cm/s). Also flows with large surface tension gradients such as weld pools should wear this tag.

Adviced literature (starter level)

  1. Wikipedia: Surface tension
  2. Wikipedia: Contact angle
  3. Wetting at MIT.edu

Adviced literature (advanced level)

  1. Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves by P.G. de Gennes et al, Springer 2004
  2. Snoeijer et al. (2013) Annual Review of Fluid Mechanics: Moving Contact Lines: Scales, Regimes, and Dynamical Transitions
  3. Quere et al. (2008) Annual Review of Materials Research: Wetting and Roughness
  4. Bonn et al. (2009) Reviews of Modern Physics: Wetting and Spreading
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Why is surface tension parallel to the interface?

A text says: The surface tension of a liquid results from an imbalance of intermolecular attractive forces, the cohesive forces between molecules: A molecule in the bulk liquid experiences cohesive forces with other molecules in all directions. …
Ajith
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How does surface tension enable insects to walk on water?

I understand that water molecules at the surface have a net inward attraction due to the lack of water molecules above them. I've been reading a bunch of articles, and they say that this inward pull causes water to act as if the surface is covered…
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What is the direction of surface tension?

How do we define the direction in which surface tension will act? Surface tension is a kind of hypothetical tension in which liquid molecules undergo tension force at the surface. Thus it should be a pulling force due to asymmetry.But many times in…
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What exerts the force of surface tension, and what does it act on?

Let me start with the simple situation that I am familiar with. This question might be kind of long. In the situation shown in the above diagram, to keep the slider in equilibrium, we must exert a force F as shown towards the right. My question is,…
Newton
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Evaporation of liquid drop due to change in surface energy

Assume that a drop of liquid evaporates by decrease in its surface energy, so that its temperature remains unchanged. What should be the minimum radius of the drop for this to be possible? The surface tension is T, density of liquid is $\rho$ and L…
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Properties of liquid and air bubbles

What is/are the properties of a liquid (e.g. viscosity, surface tension) which is conducive to formation of stable bubbles floating in air (not the bubble inside the liquid)? E.g., if soap dissolved water is bubbled through a straw, big-small air…
Gsv
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Height of Liquid Droplet on Flat Surface

How can one determine the height of a liquid droplet on a flat horizontal surface if we know the necessary physical properties of the different materials? The acceleration due to gravity is $g$. I want to look at all cases where the contact angle…
QiLin Xue
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Needle Floating on a Water Surface

So, I'm trying to find the largest radius of a needle before it ends up sinking, and I know that it's a balance of needle weight vs surface tension. However, I'm not really sure how the surface tension force is defined. In a lot of resources, I see…
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Explanation for breaking up of a stream of water into droplets

Water falling from a tap eventually breaks into droplets at a particular distance from the tap. The distance(from the tap) at which it breaks into droplets is observed to be an increasing function of the volume flux of the water flowing out of the…
Charuhas
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Why powder of a metal doesn't form the solid metal again if molecular bond is so strong?

This might seem like a stupid question but please bear with me. I've always studied and read that the molecules at the surface have higher energy than those at the interior and the explanation is also justified since very less energy is required to…
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If Surface Tension is a scalar, why is it broken into components during calculations?

In my elementary physics textbook, it is mentioned that Surface Tension is a scalar quantity. Yet, during the derivation of the ascent formula, they have broken Surface Tension into rectangular components like vectors. The diagrams in my textbook…
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How thick is the "skin" formed from surface tension?

I learnt in class that surface tension is caused by an unbalanced force at the surface of the liquid due to IMFs, forming a "skin" on the top. Does this mean that the skin is just one molecule thick? My teacher conjectured that there might some sort…
hkk
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Triangular symmetry of surface tension configuration of small grains on water

This is freshly ground pepper on water. Why is there a triangular configuration of the water around the pepper fragment? Surely all these pepper fragments have different shapes? You can clearly see one of these triangles on the lower left edge of…
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What is the effect of surface tension on an air bubble inside water?

When an air bubble is formed inside water, and while it's still inside, does a force due to surface tension act on it? Why and where does this force act? I read somewhere that a bubble would detach from the bottom of a container filled with a…
Shubham
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Height of water layer on flat surface

Let's consider some flat surface which extends to infinity in all directions. Suppose we slowly spill some water near some point of the surface. Due to surface tension, the water doesn't spread out indefinitely. If done properly, the water will…
math_lover
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