# Laplace number

The **Laplace Number** **(La)** , also known as the **Suratman Number** **(Su)** is a dimensionless number used in free surface fluid dynamics. A free surface fluid is a liquid or gas where its surface does not experience any parallel or normal shear stress. In liquids, this typically only happens when two homogeneous liquids are present. An example of this would be liquid water and air in the earth’s atmosphere.
The Laplace number can be calculated by:

Where:

- is the surface tension
- is the density
- is the characteristic length
- is the viscosity of the liquid

The Laplace number is also related to the Reynolds number and Weber number by the following equation:

## References

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