Pressure inside a Drop of Fluid

Figure 1.8 : Forces acting on a bubble membrane

 

It is because of surface tension that pressure of a liquid increases within a bubble. Consider the free-body diagram of a bubble as shown in Fig.1.8. If the force due to surface tension at the edge is balanced by the pressure force inside the bubble, we have

$$2\pi R \sigma = p \pi R^2$$ (1.24)

i.e.,

$$p = {{2 \sigma} \over {R}}$$

where p is the pressure difference between inside the drop and that outside. In addition the pressure inside the bubble is greater than that outside.

(c) Aerospace, Mechanical & Mechatronic Engg. 2005
University of Sydney