Confusion regarding surface tension direction and force balance

[palaphys]

@Steve4Physics View attachment 359594
is this an accurate diagram? As the meniscus becomes flatter and flatter, eventually the contact angle seems to tend to 180. I do not understand how this is different from a zero contact angle

ohh I get it now, this diagram is incorrect. rather,

this must be the right way of representing an obtuse contact angle.

 

[haruspex]

@Steve4Physics View attachment 359594
is this an accurate diagram? As the meniscus becomes flatter and flatter, eventually the contact angle seems to tend to 180. I do not understand how this is different from a zero contact angle

The contact angle is measured through the liquid, not through the air.
Water in a vertical capillary tube reaches up the sides of the tube forming a vanishingly thin collar. That is a (near) zero contact angle.
Mercury in a dish bulges upwards. Measuring from dish to surface of mercury through the mercury yields an angle of 135°.

 

[Steve4Physics]

@Steve4Physics View attachment 359594
is this an accurate diagram? As the meniscus becomes flatter and flatter, eventually the contact angle seems to tend to 180. I do not understand how this is different from a zero contact angle

In the above diagram:
Contact angle is about zero.
Liquid is pulled upwards by sphere.
So (Newton’s 3rd law), sphere is pulled downwards by liquid.
I.e. force on sphere is downwards.
______________________________________________

In the above diagram:
Contact angle is about 180$^o$..
Liquid is pushed downwards by sphere.
So (Newton’s 3rd law), sphere is pushed upwards by liquid.
I.e. force on sphere is upwards.

 

[palaphys]

View attachment 359596
In the above diagram:
Contact angle is about zero.
Liquid is pulled upwards by sphere.
So (Newton’s 3rd law), sphere is pulled downwards by liquid.
I.e. force on sphere is downwards.
______________________________________________

View attachment 359597
In the above diagram:
Contact angle is about 180$^o$..
Liquid is pushed downwards by sphere.
So (Newton’s 3rd law), sphere is pushed upwards by liquid.
I.e. force on sphere is upwards.

View attachment 359596
In the above diagram:
Contact angle is about zero.
Liquid is pulled upwards by sphere.
So (Newton’s 3rd law), sphere is pulled downwards by liquid.
I.e. force on sphere is downwards.
______________________________________________

View attachment 359597
In the above diagram:
Contact angle is about 180$^o$..
Liquid is pushed downwards by sphere.
So (Newton’s 3rd law), sphere is pushed upwards by liquid.
I.e. force on sphere is upwards.

Okay, now this is much more clearer. I still have another question. What about the other interfacial surface tensions, like the solid-air interfacial tension and the liquid-air interfacial tensions? Asking in a sense similar to this

 

[Steve4Physics]

Okay, now this is much more clearer. I still have another question. What about the other interfacial surface tensions, like the solid-air interfacial tension and the liquid-air interfacial tensions? Asking in a sense similar to this
View attachment 359601

Don't know what what the question means. Simply asking "What about ..." is too vague. What exactly do you want to know?

Note that there is no such thing s 'interfacial surface tension'.

Surface tension is a property of a single substance.

The interfacial force between different substances is called the interfacial tension (not interfacial surface tension).

Not something I know much about, so will leave thread at this point.

 

[palaphys]

Don't know what what the question means. Simply asking "What about ..." is too vague. What exactly do you want to know?

Note that there is no such thing s 'interfacial surface tension'.

Surface tension is a property of a single substance.

The interfacial force between different substances is called the interfacial tension (not interfacial surface tension).

Not something I know much about, so will leave thread at this point.

What exactly I want to know, is the about the pairs of surface tension forces between liquid gas, solid gas etc
as shown in the picture below, but in the context of the present problem (of sphere in liquid with contact angle roughly 180)

 

[RicoGerogi]

this is what I thought. But I was told that this is a (possibly) incorrect interpretation.

Please ask from that person how is this incorrect interpretation...

 

[haruspex]

What exactly I want to know, is the about the pairs of surface tension forces between liquid gas, solid gas etc
as shown in the picture below, but in the context of the present problem (of sphere in liquid with contact angle roughly 180)

View attachment 359603

See if https://en.wikipedia.org/wiki/Surface_energy#Interfacial_energy helps.

 

[palaphys]

See if https://en.wikipedia.org/wiki/Surface_energy#Interfacial_energy helps.

tried to read this, but it seems beyond my level. Hoping for a simpler explanation

 

[palaphys]

Alright, so what I think is that, only the S_lg meaningfully contributes to a mechanical force, as in this case, it is the only deformable meniscus. all the other interfacial surface tensions only contribute to surface energy. I would like it if someone refines my understanding on this.