Understanding Surface Tension and the Role of Force in U-Shape Wire Frames

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Discussion Overview

The discussion revolves around the concept of surface tension in the context of a U-shaped wire frame containing a sliding wire, particularly focusing on the forces involved when the frame is dipped in soap. Participants explore the mechanics of surface tension, the nature of the film formed, and the implications for work done in this system.

Discussion Character

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

Main Points Raised

  • One participant questions the formula for the force due to surface tension, suggesting that there is confusion about the number of layers in contact and the nature of the film formed between the sliding wire and the U-shaped frame.
  • Another participant asks about the number of sides the film has, leading to a discussion about whether to count edges or sides.
  • It is proposed that the film has two surfaces, each contributing to the overall surface tension, thus leading to the equation F = 2Tl.
  • Participants clarify that the film consists of two surfaces, and this understanding is reiterated in multiple responses.

Areas of Agreement / Disagreement

Participants generally agree that the film has two surfaces contributing to the surface tension, but there is some confusion regarding the terminology used (sides vs. edges) and the implications of the equations presented. The discussion remains somewhat unresolved regarding the exact interpretation of the force and work equations.

Contextual Notes

There are limitations in the assumptions made about the film's properties and the definitions of sides versus surfaces. The discussion does not fully resolve the mathematical steps related to the change in area and the work done.

Who May Find This Useful

This discussion may be useful for individuals interested in fluid mechanics, surface tension phenomena, and the physics of soap films, particularly in experimental or theoretical contexts.

AdityaDev
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If I have a U-shape wire frame and it contains a straight sliding wire and I dip this in soap, a film forms between the sliding wire and the boundary of U shape frame. Why is the force due to surface tension F = 2Tl where l is length of sliding wire?

They say there are 2 layers in contact. Which 2? There is only one film.

Also
##dW=Fdx=(2Tl)dx##
They book says 2ldx is the change in area dA. Why?
##dW = Tdx##
## hence, T= dW/dA##
 
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How many sides does the film have?
 
Bystander said:
How many sides does the film have?
4 sides. 1 stuck withe the slider. 3 bounded by frame.
 
Not edges --- sides?
 
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The film has two surfaces. There is surface tension on each surface.

Chet
 
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Bystander said:
Not edges --- sides?
Understood. 2 surfaces.
Thank you
 
AdityaDev said:
Understood. 2 surfaces.
Thank you
exper2_04.jpg
T
One surface and then flipping this vertically
upload_2014-12-11_10-6-36.png

in this way two surfaces.Each surface has surface tension so F = 2Tl.
 
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