Re: How does the surface tension of water affect the splash formed?

Cindy, thanks for the question. It is an interesting topic and as it turns 
out, your intuition was correct – surface tension does play an important 
role in the action of the drop after it hits the surface. 

When I read the question, I instantly thought of my good friend, Dr. 
Supathorn Phongikaroon (everyone calls him Supy), who did his PhD research 
on a very much related topic. The answer I give is my interpretation of 
Supy’s explanation. Supy, thank you for the help. 

First, we will discuss surface tension. Surface tension acts to minimize 
the surface area of the liquid by pulling the surface together. In this 
case, we will think of surface tension in terms of energy and an energy 
balance with the kinetic energy from the falling of the drop. The surface 
tension will try to restore the drop to a minimum surface area after 
impact while the kinetic energy of the drop will try to maximize the drop 
surface area, which is called spreading. Another important restoring 
energy that helps the surface tension keep the surface area small is the 
effect of the liquid viscosity. The higher the liquid viscosity, the more 
energy it takes to move the liquid. 

What this means for when a drop hits the surface in non-exact terms is 
that: E(Kinetic) = E(surface tension) + E(drop viscosity), where E stands 
for energy. I say non-exact because there are other terms in the equation 
that balance the units of the calculation but aren’t necessary to 
understand the concept. The surface tension and liquid viscosity energy 
terms attempt to balance the kinetic energy term. Given this information, 
a liquid with high viscosity and high surface tension will not spread as 
much as a liquid with lower values, when dropped under the same 
conditions. 

The situation changes when the drop isn’t falling and at rest on at 
surface. The drop size then is a balance between the surface energy and 
the gravitational energy. This situation is discussed in a number of fluid 
dynamics books. One example is “An Introduction to Fluid Dynamics” by 
Stanley Middleman (Wiley & Sons, 1998) page 272. The book gives a much 
more detailed approach to the problem than I have presented here. I will 
be happy to provide more detail here if necessary. 

To summarize, surface tension is important in determining the size a drop 
will attain when it drops. Congratulations, you were correct in your 
thinking.