Surface tension doubt

  • #1
528
33
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##
 
Last edited by a moderator:

Answers and Replies

  • #2
Bystander
Science Advisor
Homework Helper
Gold Member
5,203
1,225
How many sides does the film have?
 
  • #3
528
33
How many sides does the film have?
4 sides. 1 stuck withe the slider. 3 bounded by frame.
 
  • #4
Bystander
Science Advisor
Homework Helper
Gold Member
5,203
1,225
Not edges --- sides?
 
  • Like
Likes AdityaDev
  • #5
20,869
4,546
The film has two surfaces. There is surface tension on each surface.

Chet
 
  • Like
Likes AdityaDev
  • #7
2,486
83
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.
 
  • Like
Likes AdityaDev and Bystander

Related Threads on Surface tension doubt

  • Last Post
Replies
16
Views
976
  • Last Post
Replies
5
Views
847
  • Last Post
Replies
5
Views
807
Replies
2
Views
965
Replies
1
Views
956
Replies
1
Views
792
Replies
1
Views
1K
  • Last Post
Replies
2
Views
661
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
11
Views
2K
Top