# The Pressure in Bubbles

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,

Pi-Po = ΔP = 2*(2γ/R)

Where:

ΔP is the pressure difference in N/m2 or Pascals (Pa)

γ is the surface tension in N/m

R is the radius of the bubble in meters, and

2γ/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. 