Surface of a liquid behaving like a stretched membrane

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Homework Help Overview

The discussion revolves around the behavior of a liquid's surface, particularly in relation to surface tension and the forces acting on surface molecules. Participants are exploring whether the stretched nature of the surface is solely due to horizontal forces from surface tension or if it also involves vertical forces from the bulk of the liquid.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the nature of forces acting on surface molecules and whether surface tension alone can account for the behavior of a liquid's surface. There is a discussion about the implications of surface deformation and how surface tension interacts with the shape of the surface.

Discussion Status

Some participants have provided insights into the relationship between surface tension and the deformation of the liquid surface, suggesting that surface tension acts along the tangent to the curve of deformation. There is an acknowledgment of the complexity introduced by the presence of two surfaces in the case of bubbles.

Contextual Notes

Participants are grappling with assumptions about the forces involved and the implications of surface tension in supporting objects placed on the liquid surface. The discussion reflects a need for further exploration of these concepts without reaching a definitive conclusion.

andyrk
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The surface of any liquid behave like a stretched membrane. Is it because of surface tension or all the possible forces acting on a liquid molecule at the surface? I asked this question because if the furface behaves stretched because of surface tension then it means that the forces making the surface stretched are only horizontal. Whereas if the surface if behaving like a stretched membrane because of all the forces on the molecule on the surface this means the forces going into the bulk of the liquid also make it stretched. I just can't imagine the latter situation as in if we have a streched bubble membrane. It is stretched because of all the horizontal forces appears good rather than stretched because of all forces because if all the forces pull it, won't the bubble membrane burst as there would be an excess downward force?( Since there is a net force on the molecule at the top of the membrane which tries to bring the molecule at the top into the bulk.) But since the bubble membrane doesn't burst it means that it gets stretched only by the horizontal forces?
 
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andyrk said:
... if the furface behaves stretched because of surface tension then it means that the forces making the surface stretched are only horizontal

Why? That would mean that INSTANTLY when the surface is deformed away from horizontal, the surface tension would no longer support whatever it is supporting. Doesn't seem to make sense.
 
phinds said:
Why? That would mean that INSTANTLY when the surface is deformed away from horizontal, the surface tension would no longer support whatever it is supporting. Doesn't seem to make sense.

When surface is deformed then surface tension would be along the tangent to the curve(shape of depression which the object made). So it would be able to support the object. Besides its nowhere written that surface tension supports the body in consideration. Is it?
 
Last edited:
andyrk said:
When surface is deformed then surface tension would be along the tangent to the curve.
Yes. This is a correct assessment. In the case of a bubble, there are two surfaces (inside and outside of the bubble thickness), so you have to take into account the surface tension at each surface.
 

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