Welcome to All Sensors** “Put the Pressure on Us”** blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll be discussing the pressure in bubbles.

### The Pressure in Bubbles

The surface tension of the interface between liquid and gas creates a pressure difference. For a soap bubble, the pressurized bubble of air is contained within a thin, elastic surface of liquid. When the bubble bursts, the difference in pressure causes an audible pop.

The pressure difference can be calculated by using a simplified version of the Laplace pressure equation since the inner radius is essential the same as the outer radius. In this case,

P_{i}-P_{o} = ΔP = 2*(2*γ*/R)

Where:

ΔP is the pressure difference in N/m^{2} or Pascals (Pa)

γ is the surface tension in N/m

R is the radius of the bubble in meters, and

2*γ*/*R *is the Laplace pressure.

The ΔP is 2 times the Laplace pressure since there is a complete sphere instead of a semi sphere on a layer of water.

Based on the diameter, the pressure inside an air bubble in pure water, where γ = 72 mN/m at 25°C (298 K), can vary greatly.

**What do you think/Comments?**

Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.

*-Han Mai, Senior Marketing Specialist, All Sensors Corporation (hmai@allsensors.com)*