Understanding Surface Tension and its Relationship to Force Calculation

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Discussion Overview

The discussion revolves around understanding surface tension in fluids, particularly in relation to calculating force in a cylindrical container. Participants explore the relationship between surface tension, length, and directionality in force calculations, as well as the implications for non-dimensionalization in a specific context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant, Josh, questions whether to multiply surface tension by the height of the cylinder to find force, indicating uncertainty about which length to use.
  • Another participant asks for clarification on what specific force is being calculated.
  • Josh expresses confusion about the direction of the length in relation to surface tension, which is defined as force per unit length.
  • A participant introduces the concept of "surface energy" to encourage deeper consideration of the topic.
  • There is a suggestion that height may not be relevant for calculating force exerted by surface tension, prompting further inquiry into the specific application.
  • Josh clarifies that he is examining a paper involving a non-dimensional velocity term and is trying to understand how surface tension is utilized in that context.
  • Another participant notes that the line used to find force from surface tension should be on the surface or its circumference, suggesting that more details could help clarify the application.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of height in force calculations related to surface tension, and there is no consensus on the correct approach to determining the direction of the length used in these calculations.

Contextual Notes

The discussion highlights the complexity of applying surface tension concepts to specific scenarios, with participants noting the need for clarity on definitions and applications. There are unresolved questions regarding the orientation of the length in relation to the fluid surface.

member 428835
Hi PF!

Simple question here, but if we have some fluid in, say a cylinder container, with a specified surface tension, to get force would we multiply the surface tension by the height of the cylinder (if it's standing up on a circular side)? I know we multiply it by some length, but I don't understand it enough to know which one.

Please help.

Josh
 
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What force are you trying to find?
 
You know, I'm not really sure. I guess what I'm really wondering is what direction that length is, since surface tension is force per unit length.
 
Consider the concept of "surface energy." Think about that word, "surface."
 
Yea, my though is per unit height...is this wrong? Like, orthogonal to whatever surface we are talking about?
 
joshmccraney said:
Yea, my though is per unit height...is this wrong?
If you're trying to find the force exerted by the surface tension, height has nothing to do with it. You need to ask: Force on what?
 
I see what you're saying. To clarify my question entirely, I am reading a paper and there is a non-dimesnional velocity term. Now I could simply take the paper's word and use their proposed velocity, but I want to work it out and see for myself that they have correctly non-dimensionalized the velocity component. They introduce the surface tension for non-dimensional purposes. I am trying to find the direction of that length that is being used. Is this length in surface tension not always oriented in the same direction with respect to the fluid surface?
 
joshmccraney said:
I am trying to find the direction of that length that is being used. Is this length in surface tension not always oriented in the same direction with respect to the fluid surface?
When finding the force exerted by the surface tension on some line, that line is on the surface or its circumference. Perhaps if you posted more details someone will recognize exactly how the surface tension is being used in your application.
 
https://www.physicsforums.com/search/209340/?q=surface+tension&o=relevance
 

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