Hi Guys...
I have a small doubt regarding surface tension.
When calculating the relation between Pressure Difference inside and outside a Droplet and Surface Tension, we multiply Pressure Difference with Cross Sectional Area of the Droplet and equate it to the Surface tension force.
My doubt is "Why do we use Cross Sectional Area, but not Total Surface Area of the Droplet?" (Pressure acts over the whole surface)

Chestermiller
Mentor
Hi Guys...
I have a small doubt regarding surface tension.
When calculating the relation between Pressure Difference inside and outside a Droplet and Surface Tension, we multiply Pressure Difference with Cross Sectional Area of the Droplet and equate it to the Surface tension force.
My doubt is "Why do we use Cross Sectional Area, but not Total Surface Area of the Droplet?" (Pressure acts over the whole surface)
The pressure acts perpendicular to the surface of the drop. If you determine its component normal to the cross section of interest and integrate that over the surface of the drop, the result is just the pressure times the cross sectional area.